The use of probiotics, once discussed primarily in the context of alternative medicine, is now entering mainstream medicine. While an increasing number of potential health benefits are being attributed to probiotic therapies, (1) only a few have been confirmed in well-designed and conducted randomized controlled trials. There are very few adequate studies in children. This review is based on a comprehensive literature search by all authors to evaluate available evidence on the efficacy of probiotics in children in the prevention and treatment of gastrointestinal diseases. When no published data on children were available, our analysis was confined to adult studies. The problem with this approach is that data from adults may not be transferable to the pediatric population. To identify published evidence, we searched MEDLINE, EMBASE, the Cochrane Database of Systematic Reviews and the Cochrane Controlled Trials Register (all up until September 2005). We restricted our search to double-blind, randomized, controlled trials (RCTs) or their meta-analyses, using relevant keywords. The reference lists of articles identified by these strategies were also searched. Relevant key reviews and book chapters were considered. There was no restriction on language of publication. After a chapter on definitions and properties of probiotics, the review will address the different gastrointestinal entities where probiotics have been used, providing a brief framework for the potential benefit of probiotics, their possible pathophysiological role and a critical review of published data. Finally, we provide a summary of our personal opinions based on our best assessment of the evidence available.
DEFINITION AND PROPERTIES OF PROBIOTICS
A number of different definitions of probiotics have been put forward since Stillwell and Lilly introduced the term in 1965 (2). One of the most recent definitions proposed by a group of experts convened by the Food and Agriculture Organization of the United States, defined probiotics as "live microorganisms administered in adequate amounts which confer a beneficial health effect on the host" (3). The scientific basis of this definition may be questioned, as animal studies suggest that some probiotic effects can be achieved by nonviable bacteria or even by bacterial DNA (4-6). Further modification of the definition of probiotic may be warranted.
Criteria for Probiotics
Probiotics given enterally are essentially a means of delivering active constituents such as enzymes or antimicrobial substances to targets in the gastrointestinal tract (7). Thus, the benefits of a probiotic depend on its ability to preserve these active constituents against the acidity of the stomach until delivery to the target site. The criteria that must be fulfilled to classify a microorganism as a probiotic are: (1) human origin, (2) nonpathogen, (3) resistance to processing, that is, viability in delivery vehicles, (4) stability in acid and bile, (5) adhesion to target epithelial tissue, (6) ability to persist in the gastrointestinal tract, (7) production of antimicrobial substances, (8) ability to modulate the immune system and (9) ability to influence metabolic activities (8).
In humans, the most commonly used probiotics are bacteria of the genera Lactobacillus or Bifidobacterium used either as single species or in mixed culture with other bacteria. Other nonpathogenic genera, including Escherichia, Enterococcus and Bacillus, and nonbacterial organisms, such as a nonpathogenic yeast Saccharomyces boulardii, have also been used. There is some debate about whether bacteria, such as Lactobacillus bulgaricus and Streptococcus thermophilus used to ferment milk to yogurt, should be considered probiotics. These bacteria are not very resistant to conditions in the stomach and small intestine and generally do not reach the gastrointestinal tract in very high numbers. On the other hand, these bacteria have been shown to improve lactose digestion in lactase-deficient subjects and have shown some immune-enhancing effects. For these reasons, they are often considered probiotics (9).
Minimum Concentration of Probiotic Required for Beneficial Effect
A probiotic preparation must contain a certain minimum number of colony-forming units (CFUs) per dose (10). Although no dose-effect relationship study is available, the Natural Health Products Directorate of Canada currently recommends a dose of 5 billion CFUs per day for 5 consecutive days for prescription probiotics. Over-the-counter products may contain more than 50 billion CFUs per dose. Doses used in therapeutic and preventive trials vary. A daily intake of 106 to 109 CFUs is reportedly the minimum effective dose for therapeutic purposes (11). A dose-effect relationship has been suggested, but pharmacokinetic studies on probiotics are lacking and certainly needed.
Microbial Content of Probiotic Products
The beneficial effects of probiotics seem to be strain-specific and dose-dependent. Considering this, accurate labeling is essential for proper use. Published data, including our own results (12), suggest that the quality of probiotics is often inadequate (13-17). Only some products meet the definition of probiotics, that is, containing viable defined microorganisms in sufficient numbers. Products sold for medicinal purposes tend to be of higher quality than probiotics used in dairy foods or probiotic supplements. Health care professionals and patients should be aware of these variations.
TREATMENT OF ACUTE INFECTIOUS DIARRHEA
Potential for Probiotic Use
The rationale for using probiotics to treat and prevent diarrheal diseases is based on the assumption that they modify the composition of colonic microflora and act against enteric pathogens. The exact mechanism by which probiotics might exert their activity against enteropathogens in humans remains unknown. Several mechanisms have been proposed, mostly based on results of in vitro and animal studies. These include the synthesis of antimicrobial substances (eg, Lactobacillus strain GG [LGG] and Lactobacillus acidophilus strain LB have been shown to produce inhibitory substances against some gram-positive and gram-negative pathogens) (18-20), competition for nutrients required for growth of pathogens (21,22), competitive inhibition of adhesion of pathogens (23-26), and modification of toxins or toxin receptors (27,28). Other studies have shown that probiotics stimulate or modify nonspecific and specific immune responses to pathogens. Indeed, certain probiotics increase the number of circulating lymphocytes (29) and lymphocyte proliferation (30), stimulate phagocytosis, increase specific antibody responses to rotavirus vaccine strain (31), and increase cytokine secretion, including interferon-γ (30,32-34). Recently, Mack et al. (35) have shown that Lactobacillus rhamnosus GG and Lactobacillus plantarum 299v) inhibit, in a dose-dependent manner, the binding of Escherichia coli to intestinal-derived epithelial cells grown in tissue culture by stimulation of synthesis and secretion of mucins. Furthermore, probiotics have been shown to enhance mucosal immune defenses (36) and protect against structural and functional damage promoted by enteric pathogens in the brush border of enterocytes, probably by interfering with the cross-talk between the pathogen and host cells (37). It is likely that several of these mechanisms operate simultaneously, and they may well differ depending on the properties of the enteric pathogen (eg, bacterial or viral) and probiotic strain (8).
Published RCTs: Meta-analyses Assessing Probiotic Efficacy
Four meta-analyses aimed at determining the effect of probiotics in treating of acute infectious diarrhea have been published (Table 1). In the first (38), MEDLINE and the Cochrane Controlled Trials Register were searched (search date, April 2001). Ten RCTs comparing probiotics versus placebo in children aged 1 to 48 months with acute infectious diarrhea were identified. A qualitative assessment of the validity of the studies was done using the criteria of Jadad et al. (39) All studies involved hospitalized patients, except one that included a minor group of outpatients; most were conducted in developed countries. The following probiotic microorganisms were used: LGG, Lactobacillus reuteri, L. acidophilus LB, S. thermophilus lactis, L. acidophilus, L. bulgaricus and S. boulardii.
Compared with placebo, probiotics reduced the risk of diarrhea lasting more than 3 days. The relative risk (RR) in 8 RCTs involving 731 children was 0.43 (95% confidence interval [CI], 0.34-0.53) with the fixed-effects model. No significant heterogeneity was detected (P = 0.12). Among the strains, only LGG significantly and consistently reduced the risk of diarrhea lasting more than 3 days; the RR (3 RCTs, 397 children) was 0.49 (95% CI, 0.36-0.66) with the fixed-effects model. The number needed to treat (NNT) with LGG to avoid 1 case of diarrhea lasting more than 3 days was 4 (95% CI, 3-9) when using a conservative random-effects model. The NNT for S. boulardii (1 RCT) was 2 (95% CI, 2-3). Compared with placebo, probiotics significantly reduced the duration of diarrhea. The pooled weighted mean difference (WMD) in 8 RCTs involving 733 children was −18.2 hours (95% CI, −26.9 to −9.5 hours) with the random-effects model. Significant heterogeneity was detected across the included studies (P = 0.015), which appeared to be due to 1 RCT in which no significant difference between unspecified strains of S. thermophilus, L. acidophilus and L. bulgaricus and placebo was found. Excluding this study resulted in homogeneity. A meta-analysis of 4 RCTs (297 children most with confirmed rotavirus diarrhea) found that probiotics (LGG and L. reuteri) significantly reduced the duration of diarrhea over placebo; the pooled WMD was −24.8 hours (95% CI, −31.8 to −17.9 hours). No significant heterogeneity was detected (P = 0.82). A subset analysis of 53 children with invasive enteric infections from 1 RCT showed no significant difference between probiotics and placebo; the WMD was 1.3 hours (95% CI, −15.3 to 17.9 hours). No adverse effects of probiotics were reported in the included trials.
In the second meta-analysis (40), all relevant literature published from 1966 to 2000 was searched. Trials were identified by reviewing traditional biomedical literature and the complementary and alternative medicine literature. Nine RCTs (765 patients) comparing treatment with different Lactobacillus species (LGG, L. reuteri, L. acidophilus/L. bulgaricus) and placebo were included (8 of those were also identified in the previously mentioned meta-analysis). In participants who received Lactobacillus rather than placebo, the summary point estimate showed a significant reduction in diarrhea duration of 16.8 hours (95% CI, 7.2-28.8 hours) and a reduction in diarrheal stool frequency of 1.6 stools on day 2 of treatment (95% CI, 0.7-2.6). A preplanned subgroup analysis suggested a positive dose-dependent relationship between the logarithm of the daily Lactobacillus dose and the reduction of diarrhea duration in days (with a dose of >1011 CFUs/48 hours being the most effective). Adverse reactions were similar in the control and treatment groups. Two studies showed a decrease in vomiting in children given Lactobacillus.
The authors of the third meta-analysis (41) searched MEDLINE, EMBASE and CINAHL from 1966 to December 2001. Abstracts from relevant major meetings and reference lists were searched. A total of 18 double-blind and open-label RCTs performed in children younger than 5 years were included (1917 patients). The probiotic strains used were LGG, L. acidophilus, L. bulgaricus, S. thermophilus, L. rhamnosus, Yalacta (L. rhamnosus, Lactobacillus delbruckii, L. bulgaricus), L. reuteri, Enterococcus SF68, S. boulardii, S. subtilis, Bifidobacterium bifidum and Bifidobacterium infantis. The initial meta-analysis was performed on the 18 eligible RCTs (26 comparisons) using the difference in the number of days of diarrhea between patients receiving probiotics compared with controls as the outcome measure. The random-effects model gave a pooled estimate of −0.8 days of diarrhea in favor of the probiotics (95% CI, −1.1 to −0.6 days). Twenty-two of the 26 comparisons indicated a shorter duration of diarrhea in the probiotic group compared with controls. In a subanalysis of inpatient trials (23 comparative studies), the pooled estimate was −0.7 days (P < 0.001). In a subanalysis of double-blind RCTs, the pooled estimate was −0.6 days (95% CI, −1.0 to −0.3 days; P < 0.001). Subanalysis of Lactobacillus studies, showed that lactobacilli reduced the duration of diarrhea by 1.1 days (95% CI, −1.3 to −0.8 days). Similarly, the pooled estimate showed that LGG reduced the duration of diarrhea by approximately 1.2 days (95% CI, −1.6 to −0.8 days). In a subanalysis of studies evaluating probiotics other than LGG, the pooled estimate was −0.6 days (95% CI, −0.9 to −0.3 days). Thus, this meta-analysis provides evidence of the efficacy of probiotic supplements in reducing the duration of symptoms among children up to 5 years with acute nonbacterial diarrhea. Probiotics and, particularly, lactobacilli reduced the duration of the acute diarrheal episode by approximately 1 day. There was significant heterogeneity between the studies.
In the fourth and most recent meta-analysis (42) (searched up to 2002), 23 studies with a total of 1917 participants met inclusion criteria. There were 1449 infants and children (age, <18 years) and 352 adults (age, =18 years). Several probiotics were tested, all lactic acid bacilli, except for 2 studies in which the yeast S. boulardii was tested. There was wide variation in the treatment regimens according to the number of organisms administered, timing of the intervention, means of administration and duration of treatment. Trials were of varied methodological quality with different outcome criteria. Despite the variability among studies, nearly all trials showed that probiotics reduced diarrhea. The reduction was statistically significant in many studies. Pooled results show that probiotics reduced the risk of diarrhea at 3 days (RR, 0.66 days [95% CI, 0.55-0.77 days]; random-effects model; 15 studies) and the mean duration of diarrhea by 30.5 hours (95% CI, 18.5-42.5 hours; random-effects model; 12 studies). Subgroup analysis by probiotic(s), rotavirus diarrhea, national mortality rates and age of participants did not fully account for the heterogeneity.
RCTs Published After Publication of the 4 Meta-analyses
The evidence from the 4 meta-analyses above is encouraging. However, some of the recent trials not included in the meta-analyses had disappointing results. In our analysis, we will point out why we believe these studies do not subtract from the overall evidence that probiotics (and mostly lactobacilli) are effective in children with acute diarrhea. One such RCT was from a tropical developing country, where infectious agents other than rotavirus are frequently involved. The study examined the effect of LGG in 124 male inpatients (age, 1-24 months) with acute, moderate to severe, watery diarrhea (43). There was no significant reduction in diarrhea duration in subjects given LGG compared with controls (38 ± 3.8 vs 39 ± 4.6 hours; P = 0.59). This study was the first to include stool output as an outcome measure. The intervention did not result in any statistically significant difference in stool output (140 ± 171 mL/kg in the LGG group vs 185 ± 274 mL/kg in the placebo group; P = 0.81). The lack of efficacy of LGG in this study is in contrast to previous trials. It should be noted, however, that the mean duration of diarrhea in controls in this study was significantly shorter than that reported by most other studies and that the dose used (109 CFUs per day) was lower. In fact, dose-effect relationship studies previously referenced suggest that Lactobacillus is most effective above a dose of 109 to 1010 CFUs during the first 48 hours. In addition, the prevalence of breast-feeding, a factor well known to be protective during infectious diarrhea, was high in both groups.
A second RCT (n = 179) in a developing country involving boys aged 3 to 36 months with acute watery diarrhea showed no beneficial effect of LGG therapy (44). Compared with the placebo group, stool output was slightly higher in the LGG group (195 ± 172 vs 248 ± 180 mL/kg, respectively; P = 0.047). There was no significant difference between treated and placebo groups in duration of diarrhea (58.5 ± 30 vs 50.4 ± 28 hours; P = 0.2), rate of treatment failure (21.1% vs 18%; P = 0.7) and proportion of patients with unresolved diarrhea after 120 hours (12.2% vs 12.5%; P = 0.8). Again there are plausible reasons for this apparent failure of probiotics. Lactobacilli appear especially efficacious in rotaviral diarrheas, and the prevalence of rotavirus in the LGG treated group in this study was 24% compared with 39% in controls (P = 0.05). Diarrhea was more severe at study entry in the children allocated to the LGG group; that is, 60% had moderate to severe dehydration compared with 46% of controls. Lactobacillus strain GG was administered only after completing rehydration (there is evidence that early administration is more effective) and was given in a milk formula containing lactose to which almost 50% of children in both groups showed intolerance at enrollment, thus possibly masking a favorable effect of the probiotic.
Recently, a new probiotic strain, Lactobacillus paracasei strain ST11 (ST11), was tested in a double-blind, placebo-controlled RCT using criteria recommended by the World Health Organization (45). The study was conducted in Bangladesh. Two hundred thirty boys (age, 4-24 months) with diarrhea of less than 2 days' duration received L. paracasei ST11 (dose, 1010 CFUs per day) or placebo for 5 days. No effect was observed on severe rotavirus diarrhea. The probiotic treatment did, however, significantly reduce cumulative stool output (225 ± 218 vs 381 ± 240 mL/kg), stool frequency (27.9 ± 17 vs 42.5 ± 26) and oral rehydration solution intake (180 ± 207 vs 331 ± 236 mL/kg) in children with less severe nonrotavirus diarrhea compared with placebo treatment. Compared with placebo, a significantly higher proportion of nonrotavirus children receiving ST11 had resolution of diarrhea within 6 days of therapy (76% vs 49%; P = 0.004). It was concluded that ST11 has a clinically significant benefit in the management of children with nonrotavirus-induced (probably bacterial) diarrhea, but it is ineffective in those with rotavirus diarrhea. The investigators speculated that the discrepancy between their findings and those of previous studies in rotaviral gastroenteritis relates to the severity of the illness (more severely affected children were included in this study) or to the slightly longer duration of illness after intervention. The more stringent criteria for diarrhea (ie, measurement of stool volume) in the Bangladesh study may also explain less favorable results.
Another RCT conducted in Poland (46), where the enteropathogens in subjects with diarrhea are representative of pathogens causing diarrhea in other European countries, involved 176 children aged 1 month to 4 years with acute diarrhea lasting less than 72 hours. Treatment with a probiotic preparation containing 3 strains of lactic acid bacteria (L. acidophilus, B. bifidum and L. bulgaricus) at a dose of 1.6 × 109 CFUs twice daily for 5 days was not effective. Intention-to-treat analysis showed that, compared with placebo, probiotics did not shorten the duration of acute diarrhea of any etiology (61.6 ± 34 vs 54.6 ± 30 hours; P = 0.15). Limited data from subgroup analysis further suggest that the probiotics used did not reduce the duration of rotaviral diarrhea (61.1 ± 34h vs 51.6 ± 29 hours; P = 0.07). There was no difference between groups in severity of diarrhea, frequency of vomiting, weight gain and duration of hospital stay. No adverse effects of treatment were noted.
Finally, 1 positive RCT from Turkey assessed the efficacy of S. boulardii (47) in 200 children (age, 3 months to 7 years) hospitalized for acute diarrhea due, in 41.5% of cases, to rotavirus. Dose of probiotic was 250 mg daily versus placebo for 5 days. The duration of diarrhea was shorter in the S. boulardii group than the placebo group (4.7 vs 5.5 days; P < 0.05). The mean stool frequency after the second day of treatment was lower in the S. boulardii group than placebo (P < 0.005). Hospital stay was shorter in the S. boulardii group (2.9 vs 3.9 days; P < 0.001).
Summary and Recommendations
The data from well-conducted RCTs on efficacy of probiotics in children with diarrhea are encouraging. They consistently show a statistically significant benefit and moderate clinical benefit of some probiotic strains in the treatment of acute watery diarrhea, primarily rotaviral, mainly in infants and young children. The beneficial effects of probiotics in acute diarrhea in children seem to be (1) moderate in reducing duration of diarrhea by 17 to 30 hours; (2) strain-dependent, with LGG being among the most effective; (3) dose-dependent (greater for doses >1010 CFUs); (4) helpful mostly for watery diarrhea and viral gastroenteritis but not for invasive bacterial diarrhea; (5) more effective when administered early in the course of disease; and (6) more evident in children in developed countries.
In light of available evidence concerning benefits and harms, we would recommend the use of lactobacilli (in decreasing order of supporting data: LGG, L. reuteri and L. acidophilus) or S. boulardii in acute watery diarrhea (preferably in the early phase of disease) in otherwise healthy infants and young children of developed countries, in doses not inferior to 1010 CFUs per day for 5 days (high-quality data, net benefit, strong recommendation).
PREVENTION OF ANTIBIOTIC-ASSOCIATED DIARRHEA
Potential for Probiotic Use
Antibiotic-associated diarrhea (AAD) is defined as an acute inflammation of the intestinal mucosa caused by the administration of broad-spectrum antibiotics. The single bacterial agent most commonly associated with AAD is Clostridium difficile (48). However, when the normal fecal gram-negative organisms are absent, overgrowth by staphylococci, yeasts and fungi has been implicated (49). In fact, most episodes of AAD in childhood are not due to C. difficile (50). The rationale for the use of probiotics in AAD is based on the assumption that the key factor in the pathogenesis of AAD is a disturbance in normal intestinal microflora.
Six RCTs have evaluated different probiotics for the prevention of AAD in children (Table 2).
One small RCT of 38 children showed that those treated with L. acidophilus and L. bulgaricus did not significantly prevent AAD (51). Another negative double-blind RCT investigated the effect of L. acidophilus and B. infantis (52). These 2 studies have methodological drawbacks (small sample size and/or failure to use diarrhea as an end point), which preclude drawing reliable conclusions.
Two RCTs assessed LGG in ambulatory children on short-term (7-10 days) antibiotic therapy for respiratory tract infections. The first RCT (53) showed that, in children receiving antibiotics (93 on probiotic and 95 controls), coadministration of LGG reduced both the incidence (8% vs 26%; RR, 0.29 [95% CI, 0.13-0.61]; NNT, 6 [95% CI, 4-13]) and duration (4.7 vs 5.9 days; P = 0.05) of diarrhea defined as ≥2 liquid stools per day for ≥2 days. By day 10, stool frequency was significantly lower in the LGG group than in the placebo group (mean number of stools per day, 1.4 vs 2.0; P < 0.02). Episodes of diarrhea in this study were mild, did not lead to dehydration or hospitalization and resolved shortly after cessation of antibiotic therapy.
The second RCT (54) defined diarrhea more conservatively as ≥3 liquid stools per day for ≥2 consecutive days. One hundred nineteen children were entered (61 in the experimental group and 58 in the control group). Lactobacillus strain GG reduced the risk of diarrhea from 16% to 5%, a difference that did not reach statistical significance. The severity of diarrhea as measured by stool frequency (mean, 5 per day; range, 3-6 per day) and duration of diarrhea (mean, 4 days; range, 2-8 days) did not significantly differ between groups. The episodes of diarrhea in this study were also mild, did not lead to dehydration or hospitalization, did not require additional treatment and resolved shortly after cessation of antibiotic therapy.
A recent RCT (55) investigated the impact on AAD of S. boulardii in 269 children (age, 6 months to 14 years) with otitis media and/or respiratory tract infections. In this double-blind RCT, children received antibiotic treatment plus 250 mg of S. boulardii (n = 132) or placebo (n = 137) orally twice daily for the duration of antibiotic treatment. Analyses were based on allocated treatment and included data from 246 children. Patients on S. boulardii had a lower prevalence of diarrhea (≥3 loose or watery stools per day for ≥48 hours occurring during or up to 2 weeks after the antibiotic therapy) than those who received the placebo (7.5% vs 23%; RR, 0.3 [95% CI, 0.2-0.7]; NNT, 8 [95% CI, 5-15]). No adverse events were observed. This was the first RCT evidence that S. boulardii reduces the risk of AAD in children.
Another RCT of a commercial probiotic containing Bifidobacterium lactis and S. thermophilus involved 157 infants, 6 to 36 months of age. The study found a significant difference in the incidence of AAD in children receiving probiotic-supplemented formula (16%) compared with nonsupplemented children (31%; RR, 0.52 [95% CI, 0.52-0.95]; NNT, 7 [95% CI, 4-62]).(56) As no attempt was made to identify the etiology of diarrhea, one cannot exclude the possibility that some episodes of diarrhea were of infectious origin.
Summary and Recommendations
In conclusion, RCTs in children provide evidence of a moderate beneficial effect of LGG, B. lactis and S. thermophilus and S. boulardii in preventing AAD. No data on efficacy of other probiotic strains are available in children.
Because the previously mentioned probiotics have been shown capable of providing reasonable protection against the development of AAD, we believe that their use is probably warranted whenever the physician feels that preventing this usually self-limited complication is important (high-quality data, net benefit, moderately strong recommendation).
TREATMENT OR PREVENTION OF RECURRENT C. DIFFICILE DIARRHEA
Most children who have an episode of C. difficile diarrhea, whether antibiotic-associated or sporadically acquired, respond to the proper antibiotic treatment with eradication of infection. Up to 20%, however, experience recurrent infection. The use of probiotics, especially S. boulardii and LGG, has been advocated to prevent recurrences. Nevertheless, a recent systematic review concluded that available evidence does not support probiotic treatment during antibiotic therapy to prevent C. difficile diarrhea and is inadequate to justify treatment of existing C. difficile diarrhea in adults (57). Despite some anecdotal reports of efficacy, no RCT investigating the use of probiotics to treat or prevent C. difficile in children has been conducted.
Summary and Recommendations
We concur with McFarland (58) that well-done RCTs addressing the role of probiotics in C. difficile AAD are needed. Currently, we conclude that there is no evidence to support the use of any probiotic to prevent the recurrence of C. difficile infection or to treat existing C. difficile diarrhea.
PREVENTION OF NOSOCOMIAL DIARRHEA
Potential for Probiotic Use
Nosocomial diarrhea refers to any diarrhea contracted in a health care institution. In children, it is commonly caused by enteric pathogens especially rotavirus (59). Depending on the population, type of hospital and standard of care, the reported incidence ranges from 4.5 (60) to 22.6 (61) episodes per 100 admissions. Nosocomial diarrhea may prolong hospital stays and increase medical costs. Although hand washing is the essential infection control measure, other cost-effective measures to prevent nosocomial diarrhea are being evaluated.
Four RCTs examining the use of probiotics to prevent diarrhea in infants and young children admitted to hospitals for reasons other than diarrhea were identified. Two evaluated LGG, and 2 assessed a combination of B. bifidum (recently renamed B. lactis) and S. thermophilus (Table 3).
RCTs with LGG
The 2 studies on prevention of nosocomial diarrhea by LGG evaluated young children hospitalized for relatively short stays produced conflicting results (62,63). One double-blind RCT of 81 children (1-36 months) showed that 6 × 109 CFUs of LGG administered orally twice daily significantly reduced the risk of nosocomial diarrhea compared with placebo (6.7% vs 33.3%; RR, 0.2 [95% CI, 06-0.6]; P = 0.002) (62). Four patients would need to have been treated with LGG to prevent one from developing nosocomial diarrhea in this study (NNT, 4 [95% CI, 2-10]). Rotavirus was the predominant identified etiologic agent. The prevalence of rotavirus infection did not differ in the probiotic-treated and control groups (20% vs 27.8%; RR, 0.72 [95% CI, 0.33-1.56]; P = 0.4). However, the use of probiotics significantly reduced the risk of rotavirus gastroenteritis (2.2% vs 16.7%; RR, 0.13 [95% CI, 0.02-0.8]; P = 0.02). Seven patients would need to have been treated with LGG to protect one from developing nosocomial rotavirus gastroenteritis (NNT, 7 [95% CI, 3-40]) (62).
The second RCT evaluating LGG in the prevention of diarrhea involved 220 children (1-18 months). Whereas breast-feeding was effective, 1010 CFUs of LGG administered orally once daily did not prevent nosocomial rotavirus infections compared with placebo (25.4% vs 30.2%; RR, 0.84 [95% CI, 0.55-1.29]; P = 0.4). However, the rate of symptomatic rotavirus gastroenteritis was lower in children receiving LGG compared with placebo (13% vs 21%; RR, 0.6 [95% CI, 0.35-1.16]; P = 0.13) (63).
Thus, the available data do not provide strong evidence for the routine use of LGG to prevent nosocomial rotavirus diarrhea in infants and toddlers. Further research addressing the effect of twice daily versus once daily dosing seems reasonable, as this was the main difference between the 2 previously described RCTs.
RCTs with B. bifidum and S. thermophilus
The first of 2 RCTs addressing the efficacy of B. bifidum and S. thermophilus in preventing nosocomial diarrhea included 55 infants (5-24 months) admitted to a chronic care hospital for relatively long stays. In this study, the administration of a standard infant formula supplemented with B. bifidum and S. thermophilus reduced the prevalence of nosocomial diarrhea compared with placebo (7% vs 31%; RR, 0.2 [95% CI, 0.06-0.8]). The authors estimated that 5 patients would need to receive probiotic-supplemented formula to protect one from developing nosocomial diarrhea (NTT, 5 [95% CI, 3-20]). The risk of rotavirus gastroenteritis was significantly lower in those receiving probiotic-supplemented formula (RR, 0.3 [95% CI, 0.09-0.8] NNT, 4 [95% CI, 3-18]) (64). Bifidobacterium bifidum and S. thermophilus significantly reduced the rate of rotavirus shedding in treated infants. This is an important observation, as a decrease in rotavirus shedding may lead to less environmental exposure and a lower rate of rotavirus transmission in hospitalized children. However, when the results of the study were presented as the number of episodes per patient-month rather than as the percent of patients in each group with diarrhea, the difference between the probiotic-treated and control groups was not significant (2 episodes per 76.5 patient-months vs 8 episodes per 71.8 patient-months, respectively; incidence rate ratio, 0.23 [95% CI, 0.02-1.18]). The latter means of data presentation (percentage of patients) is more appropriate for long-term prevention trials in patients followed up for different periods, as more than 1 episode per patient is possible.
The second, more recent RCT included 90 healthy infants younger than 8 months who were living in residential nurseries or foster care centers. Although residential care settings differ from hospital settings, residents are also at increased risk for diarrheal illnesses, and the mode of acquiring diarrhea is similar. In this study, milk formula supplemented with viable B. lactis strain Bb12 did not reduce the prevalence of diarrhea compared with placebo (28.3% vs 38.7%; RR, 0.7 [95% CI, 0.4-1.3]) (65).
Summary and Recommendations
In summary, there is conflicting evidence from 2 RCTs on the efficacy of LGG in preventing nosocomial diarrhea. One small RCT suggests a benefit of B. bifidum and S. thermophilus in sick infants admitted to the hospital, but no such benefit has been identified in healthy children in residential care settings. In light of these conclusions, we do not believe that there is currently enough evidence to recommend the routine use of probiotics to prevent nosocomial diarrhea. As this is a field of potentially great benefit, there is a need for large, well-designed RCTs.
PREVENTION OF ACUTE GASTROINTESTINAL AND RESPIRATORY TRACT INFECTIONS
Potential for Probiotic Use
Prevention is the most important challenge posed by childhood diarrheal diseases, particularly in developing countries. In the past several years, enormous efforts have been made to develop safe and effective vaccines against enteric infections (66). The most recent data on rotavirus vaccines are very encouraging, but other enteric pathogens still await their turn. Children attending day care centers are also at high risk for developing gastrointestinal and respiratory infections. The successful prevention of these infections could be beneficial to families and society. It has been proposed that the continuous use of probiotics might, by providing an immunologic stimulus, be useful in preventing infectious diseases commonly encountered by young children.
Studies of probiotics for prevention of acute symptomatic gastrointestinal and respiratory infections are summarized in Table 4. Oberhelman et al. (67) evaluated the effect of probiotics in preventing community-acquired diarrhea in Peru, in a community with a high burden of diarrheal disease. This study of 204 undernourished infants showed that there were significantly fewer diarrhea episodes in children treated with LGG compared with placebo (5.21 vs 6.02 episodes per child per year; P = 0.028). The benefit was particularly evident in non-breast-fed children aged 18 to 29 months (4.69 vs 5.86 episodes per child per year; P = 0.005).
Another RCT (68) performed in Finland examined the effect of the long-term consumption of probiotic milk containing LGG (in a dose 2 × 108 CFUs per day) on the incidence of diarrhea and respiratory infections in 571 children aged 1 to 6 years who attended day care centers. No significant differences were noted in the number of days with diarrhea or in the proportion of children without diarrhea during the 7-month study. However, the group treated with LGG experienced a 16% reduction (95% CI, 2%-27% reduction) in the number of days of absence due to gastrointestinal and respiratory infections (4.9 vs 5.8 days; P = 0.03) and a reduced risk of having at least 1 course of antibiotic prescribed for respiratory tract infection (44% vs 54%; absolute risk reduction, 9.6% [95% CI, 1%-18.2%]; P = 0.03).
Thibault et al. (69) assessed the prevalence of acute diarrhea in more than 900 infants (4-6 months of age, "regularly" exposed to child care and/or living at home with at least 2 siblings) fed for a prolonged period a formula enriched with Bifidobacterium breve and S. thermophilus 065. Although the results showed that incidence and duration of diarrhea episodes, as well as number of hospital admissions, did not differ significantly between the 2 groups, the episodes were less severe in the probiotic-supplemented group. There were fewer cases of dehydration (2.5% vs 6.1%; P = 0.01), fewer medical consultations (46% vs 57%, P = 0.003), fewer ORS prescriptions (42% vs 52%, P = 0.003) and fewer formula changes (59% vs 75%, P = 0.0001) in infants taking probiotic-supplemented formula compared with those on standard formula.
Pedone et al. (70) evaluated the efficacy of Lactobacillus casei strain DN-114 001 in RCT involving 928 children (age, 6-24 months), of whom 779 (84%) were analyzed. The investigators showed that healthy children who received milk fermented by yogurt cultures and L. casei strain DN-114 001 had a significantly reduced incidence of diarrhea compared with children who received traditional yogurt (15.9% vs 22%; RR, 0.7 [95% CI, 0.5-0.97]; NNT, 17 [95% CI, 9-159]). This difference was observed during the supplementation period but was no longer statistically significant 6 weeks after the end of supplementation. The investigators believe that this suggests that the beneficial effect of L. casei requires regular intake of the probiotic. Methodological concerns about this study are that the method of concealing allocation to the intervention groups was not made clear, that an intention to treat analysis was not carried out and that there was no placebo group.
Saavedra et al. (71) evaluated the tolerance and safety of long-term consumption of probiotics. Children (age, 3-24 months) recruited from 27 day care centers in the United States were assigned to receive (1) a standard formula supplemented with B. lactis (strain Bb12) and S. thermophilus at a concentration of ≍1 × 107 CFUs per gram, high-supplement formula, (2) the same formula supplemented at a concentration of 1 × 106 CFUs per gram, low-supplement formula or (3) the same formula without any supplementation (placebo formula). Both supplemented formulas were well accepted and were associated with a lower frequency of reported colic or irritability (P < 0.001) and a lower frequency of antibiotic use (P < 0.001) than was the unsupplemented formula. There were no significant differences between groups in growth, health care attention seeking, day care absenteeism or other health variables.
Finally, in a recent, prospective, 12-week, double-blind RCT (72), treatment with 2 probiotic organisms was compared with treatment with a placebo in 210 healthy infants (age, 4-10 months) attending child health care centers. The 3 groups received formula supplemented with B. lactis (Bb-12), L. reuteri or no probiotic. The probiotic concentration of the formula was 1 × 107 CFUs per gram. Infants fed placebo formula had more diarrhea episodes than those supplemented with L. reuteri or B. lactis, respectively (0.31 [0.22-0.40] vs 0.13 [0.05-0.21] vs 0.02 [0.01-0.05]), and had episodes of longer duration (0.59 [0.34-0.84] vs 0.37 [0.08-0.66] vs 0.15 [0.12-0.18] days). These effects are statistically significant, but their clinical importance is questionable. Children on L. reuteri also experienced significantly fewer febrile episodes, had fewer clinic visits, fewer absences from child care and had fewer prescriptions for antibiotics. The importance of this study is that it represents 1 of the few controlled studies comparing different species of probiotic microorganisms (L. reuteri and B. lactis) for a specific indication.
Summary and Recommendations
In conclusion, these RCTs have provided evidence of a modest effect (statistically significant but of questionable clinical importance) of some probiotic strains preventing gastrointestinal and respiratory infections in healthy infants and children. Future large-scale and long-term studies should establish preferred duration, dosage and organism producing optimum clinical effects. We believe that there is a potential role for probiotics in preventing respiratory and gastrointestinal infections in healthy children. However, currently available evidence is not strong enough to give specific recommendation concerning these indications.
Potential for Probiotic Use
Preterm neonates in neonatal intensive care units (NICUs) develop a colonic bacterial flora radically different from that of healthy term infants. Microorganisms typical of the breast-fed infant appear late in stool culture. In addition, reduced exposure to maternal microflora, the utilization of sterile feedings and the widespread use of antibiotics in the NICU all diminish the newborn's exposure to commensal bacteria and decrease their chances of effectively colonizing the gut. Under these circumstances, the colon may actually become a reservoir of antibiotic-resistant, potentially harmful organisms. The predominant bacterial flora in preterm NICU babies is made up of Staphylococcus, Enterobacteriae, such as Klebsiella, and Enterococci. The most common anaerobes are Clostridia spp. Only a small minority of NICU neonates is colonized by bacteria that predominate in healthy, term, breast-fed babies such as bifidobacteria. This abnormal colonization is thought to contribute to the development of necrotizing enterocolitis (NEC), the most common abdominal emergency of preterm infants in the NICU (73).
Early studies on the possible role of probiotics in preterm infants focused on safety and on their capacity to modify intestinal microflora. More recently, several RCTs have addressed probiotic efficacy in preventing NEC.
To date, 3 RCTs have evaluated the effect of probiotics in preventing NEC (Table 5). The purpose of the first study (74) was to evaluate the effectiveness of LGG supplementation in reducing the incidence of NEC, bacterial sepsis and urinary tract infections in preterm infants. Newborn infants (n = 585) of gestational age of less than 33 weeks or birth weight of less than 1500 g were randomized to receive standard milk formula supplemented with LGG at a dose of 6 × 109 CFUs once daily until discharge, starting with the first feed, or placebo. Although NEC (1.4% vs 2.7%) and urinary tract infections (3.4% vs 5.8%) were less frequent in the probiotic group than in the controls, the differences were not significant. Bacterial sepsis was more frequent in the probiotic group (4.4%) than in the placebo group (3.8%), but this difference too was not statistically significant either.
Another well-designed trial from China (75) compared the incidence of NEC and the mortality of very low-birth-weight (VLBW) infants fed breast milk with or without added probiotics. The study was prospective, conducted over 4.5 years in VLBW infants admitted to NICUs at level 3 neonatal centers. Infants with birth weight of less than 1500 g, who started to feed enterally and survived beyond the seventh day of life, were eligible. Infants were randomized to receive breast milk (mother's milk or banked milk) (n = 187) or breast milk supplemented with L. acidophilus and B. infantis, 125 mg/kg per dose twice daily (n = 180), until discharge. Oral feeding was started when the infant met criteria for enteral feedings. Feedings were advanced in increments of no more than 20 mL/kg per day and were stopped if gastric aspirate was more than 50% of the previous feeding twice with abdominal distention. Infants weighing less than 1000 g received total parenteral nutrition until half of their energy was supplied orally. Necrotizing enterocolitis was classified by Bell's classification. Primary outcome measures were the incidence of NEC and death. Secondary outcome measures were the severity of NEC and sepsis. The composite end point of death and NEC was significantly lower in the probiotic group compared with controls (5% vs 12.8%, respectively; P = 0.009; RR, 0.4 [95% CI, 0.2-0.8]; NNT, 13 [95% CI, 8-49]). The incidence of NEC alone was lower in the probiotic group than in the controls (1.1% vs 5.3%, P = 0.04; RR, 0.2 [95% CI, 0.05-0.8]; NNT, 24 [95% CI, 12-142]). There were 6 cases of severe NEC in the control group and none in the probiotic group (P = 0.03). The incidence of culture-proven sepsis was lower in the probiotic group (22% vs 36%, P = 0.03; RR, 0.6 [95% CI, 0.4-1.03]).
In a recent RCT from a neonatology unit in Israel, feeding a daily supplement of a probiotic mixture (B. infantis, S. thermophilus and B. bifidum) at 109 CFUs per day reduced the incidence and severity of NEC in VLBW (≤1500 g) infants. The incidence of NEC was 4% in the probiotic group versus 16.4% in controls, an RR reduction of 75% (95% CI, 21%-92%) and NNT of 9 (95% CI, 5-39). The severity of NEC was less severe in the probiotic group (P = 0.005). Three of 15 infants with NEC died, all in the control group (76). One possible explanation for the greater treatment effects in the latter 2 RCTs compared with the first study may be the use of a mixture of probiotic strains rather than a single strain. Another explanation may be differences in the incidence of NEC at different institutions.
Summary and Recommendations
In summary, not only is there a strong conceptual rationale for the use of probiotics in the prevention of NEC in preterm babies, but also recent results of RCTs show their efficacy. This clearly is one of the most exciting probiotic applications, but given the potential risks of administering large doses of live bacteria to immunologically immature babies, often also affected by comorbidities, more well-conducted, large-possibly multicenter-trials are required to provide convincing evidence of efficacy and safety of already studied as well as other probiotic strains before their use for this indication can be recommended.
A further word of caution regarding the use of probiotics in preterm babies comes from a report documenting the occurrence of LGG-induced bacteremia and sepsis in 2 critically ill infants (77). Although both patients had important underlying disorders, this warning should not be ignored.
PROBIOTICS IN IRRITABLE BOWEL SYNDROME
Potential for Probiotic Use
Irritable bowel syndrome (IBS) encompasses a group of functional bowel disorders in which abdominal discomfort and pain are often associated with an altered bowel habit and bloating with no obvious organic cause. Surveys of western populations have revealed IBS in 15% to 20% of adolescents and adults, with a higher prevalence among women. In 1 pediatric study, children with IBS accounted for 25% to 50% of visits to a gastroenterology clinic (78). Irritable bowel syndrome presents a significant therapeutic challenge. Currently available therapies provide at best only symptomatic relief, and none influences the natural course of the disorder.
What are the theoretical bases for the potential benefit of probiotics in IBS? In normal conditions, gut motility, absorption, permeability and secretion are influenced by the interactions between intestinal microflora and the colonic mucosa (79). Early studies in mice have reinforced this correlation (80,81). Further evidence (82) has led to the belief that shifts in commensal bacterial populations may contribute to the disordered motility, visceral hypersensitivity, abnormal brain-gut interactions and immune activation associated with IBS. Several studies (83,84) have identified differences in gut microbiota of IBS patients compared with normal individuals. Commensal organisms such as lactobacilli and bifidobacteria have been observed to be significantly reduced in diarrhea predominant IBS (85). Alterations within the major anaerobic species have been recognized, from the gram-positive Bacteroides and Bifidobacterium spp to more gram-negative organisms such as Clostridium spp (83). These data highlight an important but controversial conclusion that disparities in microbial populations and abnormal colonic fermentation are possible causes for IBS symptoms. Live probiotic bacterial supplements might theoretically benefit IBS symptoms by improving the intestinal microbial balance, reduce fermentation by pathogenic organisms (86) and regulate the motility of the digestive tract (87).
Studies in Adults
While various preparations have been investigated in adults with IBS, only few, mostly small, controlled studies have been published (Table 6). In most reported studies, beneficial results were seen (88-96), although in 3, the interventions produced no significant benefit (97-99).
Why is there variability of probiotic effects in the treatment of IBS? Results of a recent study by O'Mahony et al. (100) speak to this question. The authors demonstrated superiority of a B. infantis over Lactobacillus salivarius (each in a dose of 1 × 1010 CFUs) compared with placebo for each of the symptoms of IBS (abdominal pain/discomfort, distention/bloating and difficult defecation). The study included quality-of-life assessment, stool microbial studies and blood sampling for estimation of peripheral blood mononuclear cell release of interleukin (IL) 10 and IL-12 at the beginning and end of treatment. The authors found that patients treated with B. infantis (but not with L. salivarius) experienced a greater reduction in symptom scores than placebo-treated patients. At baseline, IBS subjects had an abnormal IL-10/IL-12 ratio, suggestive of a proinflammatory state. The ratio normalized in patients given B. infantis alone. The investigators believe that normalization of the cytokine ratio could be attributed to immunomodulatory and anti-inflammatory effects of B. infantis. Furthermore, they believe that these observations are evidence for a clearly defined benefit of a single-organism probiotic preparation in IBS patients. The findings suggest that some probiotics may be more effective than others in improving the outcome in IBS.
Studies in Children
Only 1 RCT on probiotics for IBS in children has been published. Fifty children fulfilling the Rome II criteria for IBS were given LGG or placebo for 6 weeks. The probiotic treatment was not superior to placebo in relieving abdominal pain (40% response rate in placebo group vs 44% in the LGG group). There was no difference in other gastrointestinal symptoms, except for a lower incidence of perceived abdominal distention (P = 0.02 favoring LGG) (101). A multicenter RCT of VSL#3 for the treatment of pediatric IBS is currently under way.
Summary and Recommendations
No recommendation on use of probiotics in children with IBS can be made, given the almost complete lack of published trials. To show a benefit, larger cohorts of patients in randomized and double-blind studies with longer duration of therapy are essential.
PROBIOTICS IN INFLAMMATORY BOWEL DISEASE
Potential for Probiotic Use
It is currently estimated that 40% to 70% of children with inflammatory bowel disease (IBD) (102,103) regularly use alternative medicine preparations, including probiotics to supplement or even replace prescribed medications. There are sound theoretical reasons to predict a potential benefit of probiotic treatment in IBD, but unfortunately, there are few data to support this prediction. The prediction of probiotic efficacy in IBD rests mainly on the concept that the intestinal microflora has a role in the pathogenesis of IBD (104). This concept derives from several direct and indirect lines of investigation: the occurrence of Crohn disease and ulcerative colitis in areas of the gastrointestinal tract with the higher concentrations of microorganisms; the finding that up to 50% of children with Crohn disease have a mutation of the CARD 15 gene coding for the NOD2 protein (105), a central modulator of the interaction between bacterial surfaces and intestinal epithelium (106); the notion that abolishing contact between bacteria and mucosal surface in Crohn disease (eg, by diversion of the fecal stream) reduces the inflammation; and finally, the experimental finding that in all animal models of IBD studied, the congenital absence of intestinal bacteria prevents the onset of the IBD equivalent. In several animal models of colitis, probiotics have shown efficacy: LGG, L. reuteri, L. plantarum and the probiotic mixture VSL#3 have been found capable of reducing pathological changes and, in some instances, reducing the production and release of proinflammatory cytokines.
Studies in Adults
Studies of probiotics for IBD are summarized in Table 7.
Ulcerative Colitis: Published RCTs
There are a few studies of probiotic therapy in adult with ulcerative colitis. Escherichia coli Nissle 1917 has been found to be as useful as mesalamine in maintaining remission in adults with ulcerative colitis (107,108). In a recent RCT (109), the administration of 200 mg/d of this probiotic for 1 year in 162 patients in remission resulted in a relapse rate of 36.4% versus 33.9% in 165 controls taking mesalamine only.
In a small RCT, a milk fermented by bifidobacteria was administered to 11 patients, whereas 10 received a control milk, for 1 year. Colonoscopies, general blood markers and examinations of intestinal flora, including the analysis of fecal organic acids, were performed initially and after 1 year. Symptoms recurred in 3 of the 11 treated patients versus 9 of 10 controls. The cumulative exacerbation rate was lower in the bifidobacteria group (P = 0.018) (110).
Treatment and Prevention of Pouchitis: Published RCTs
A considerable portion of ulcerative colitis patients with ileoanal pouch after colectomy will eventually develop pouchitis. A prospective RCT in adults with pouchitis followed up patients treated with antibiotics, the probiotic mixture VSL#3 or placebo. During the year after treatment, 3 (15%) of the 20 treated patients experienced a relapse versus all 20 patients in the placebo group (111). More recently, the same group confirmed these observations in a subsequent RCT (112), by showing that if VSL#3 is given continuously after pouch creation, pouchitis occurred in only 2 of the 20 treated patients (10% vs 40% of controls). In the same study, probiotic-treated patients experienced fewer daily stools than controls (average, 5 vs 8 bowel movements per day).
No data are available on the possible efficacy of probiotics in children with ileoanal pouch.
Crohn Disease: Published RCTs
Results of RCTs in adult with Crohn disease are mixed. Two small RCTs suggest that S. boulardii compared with placebo (113), or S. boulardii plus mesalamine compared with mesalamine alone (114), is effective in maintaining remission. The conclusions of these 2 trials are limited by the small number of patients and the concomitant use of other drugs active in Crohn disease. One RCT found that E. coli Nissle was superior to placebo in preventing relapse (115). No benefit of LGG was reported by Prantera et al. (116) who administered LGG daily for 12 months to patients who had undergone surgery. Three (16%) of 23 treated patients had a relapse versus 2 (10%, not significant) of 22 placebo-treated patients.
Studies in Children
Crohn Disease: Published RCTs
The use of probiotic therapy for pediatric patients with Crohn disease is limited to one RCT showing no impact (117). Seventy-five pediatric patients (age, 5-21 years) with Crohn disease in remission from 11 centers in the United States were randomized to receive LGG (n = 39) or placebo (n = 36). Interim data were reviewed by the Data and Safety Monitoring Board (DSMB) 42 months after initiation of the study when 75 patients had been enrolled. Data were available on 71 subjects at the DSMB meeting and were analyzed for both safety and efficacy. The DSMB concluded that there was no difference in adverse events in the 2 groups and no difference between the 2 groups in time to relapse and therefore recommended closure of the study. In the final data set of 75 patients, median time to relapse was similar for the 2 study groups (LGG group: 11.6 months [range, 7.9-15.3 months] and placebo group: 12.8 months [range, 8.3-17.4 months]). The proportion of patients relapsing was not different between the 2 groups. This study concluded that LGG did not prolong time before relapse in children with CD when given as an adjunct to standard therapy.
Summary and Recommendations
Evidence from RCTs supports the use of high doses of VSL#3 for the primary and secondary prevention of pouchitis in adults. There is inadequate evidence in adults and none in children for using probiotics for induction of remission or maintenance of medical or surgical remission in Crohn disease. Further studies in children are warranted, especially in the area of pouchitis. Until then, no recommendations for the use of probiotics in children with IBD can be made.
PROBIOTICS FOR FUNCTIONAL CONSTIPATION
Potential for Probiotic Use
Complaints related to constipation account for 3% of visits to pediatric outpatient clinics and 25% of pediatric gastroenterology consultations (118-120). The aim of the treatment is to resolve fecal impaction and to restore bowel habits to where stools are soft and passed without discomfort. Although osmotic stool softeners are widely used for this purpose, they fail to provide sustained relief of symptoms in many patients, prompting interest in adjunctive treatments. One rationale for using probiotics to treat constipation is a report of dysbiosis in the intestinal flora of patients with chronic functional constipation (121). Another is the suggestion that probiotics might improve intestinal motility (122).
Studies in Adults: Published RCTs
In adults, 1 double-blind randomized trial showed that a probiotic beverage containing L. casei Shirota improved gastrointestinal symptoms in 70 adults with chronic constipation. A small, nonrandomized, open clinical trial in 28 elderly subjects showed that supplementation of juice with a combination of L. rhamnosus and Propionibacterium freudenreichii resulted in a 24% increase in defecation frequency compared with a group receiving L. reuteri-supplemented juice and an unsupplemented group. No reduction in laxative use was observed (123,124).
Studies in Children: Published RCTs
Only 1 RCT addressed the use of probiotics in the treatment of children with constipation. Eighty-four children 2 to 16 years with less than 3 spontaneous bowel movements per week for at least 12 weeks were enrolled in a double-blind RCT in which they received 70% lactulose, 1 mL/kg per day, plus 109 CFUs of LGG (experimental group, n = 43) or a placebo (control group, n = 41) orally twice daily for 12 weeks. The primary outcome measure was treatment success, and analyses were performed on an intention-to-treat basis. Treatment success, defined as more than 3 spontaneous bowel movements per week with no fecal soiling, was similar in the control and experimental groups at 12 weeks (68% vs 72%, respectively) and at 24 weeks (65% vs 64%, respectively). The groups also did not differ in the mean number of spontaneous bowel movements per week or episodes of fecal soiling per week at 4, 8 and 12 weeks. Adverse events and overall tolerance did not differ between groups. It was concluded that LGG, as used in this study, was not an effective adjunct to lactulose in treating constipation in children (125).
Summary and Recommendations
In summary, at present, there is no evidence to recommend the use of probiotics in the children with constipation.
PROBIOTICS FOR HELICOBACTER PYLORI INFECTION
Potential for Probiotic Use
The role of the gram-negative bacillus Helicobacter pylori in the pathogenesis of chronic gastritis and peptic ulcer in adults and children and as a risk factor for gastric malignancy in adults is widely accepted. Studies have shown that various lactobacilli (eg, Lactobacillus johnsonii La1, L. acidophilus CRL 639 and L. casei) or their metabolic products can inhibit or kill H. pylori in vitro (126,127), suggesting that probiotics may have a place as adjunctive treatment of H. pylori infection.
Studies in Adults: Published RCTs
The role of probiotics in the treatment and prevention of H. pylori infection was recently reviewed by Hamilton-Miller (128). He identified 6 clinical trials (180 patients) in which a probiotic was used alone. Five of the studies produced encouraging results: in 3, breath-test readings were significantly reduced; in 2 others, some patients were cleared of infection. Only a few studies were randomized, double-blind, placebo-controlled trials. In 9 additional randomized trials (129-137) (6 were found by Hamilton-Miller (128), and 3 were identified by us) involving 834 patients, probiotics were added to a therapeutic regimen of antibiotics. There was an increased eradication rate in 2 studies (129,134) and reduced side effects in 7 (131-137) (Table 8). Trials in which fermented milk products or whole cultures of lactobacilli were used tended to yield better results than when the probiotic was taken in the form of bacteria alone.
Studies in Children: Published RCTs
There has only been 1 RCT (138) evaluating whether probiotics could improve H. pylori eradication in children or reduce the side effects of treatment. Eighty-six children with H. pylori infection and dyspepsia for more than 3 months were allocated to a 7-day course of therapy with omeprazole, amoxicillin and clarithromycin or the same therapy supplemented with fermented milk containing L. casei DN-114 001, 1010 CFUs daily, for 14 days. Eradication was assessed by H. pylori stool antigen test and 13C-urea breath test 4 weeks after treatment cessation. Helicobacter pylori infection was considered eradicated if both tests were negative. Both per protocol and intention-to-treat analyses were performed. The latter analysis showed that the probiotic-supplemented group had a greater eradication rate than placebo (84.6% vs 57.5%; relative benefit, 1.47 [95% CI, 1.1-2]; NNT, 4 [95% CI, 3-13]). The incidence of side effects did not differ between groups. Drug compliance was good throughout the study. Perhaps the most exciting and clinically relevant finding of this trial is increased eradication rate, which is in contrast to many studies in adults. It should be noted that, in this particular study, the eradication rate in the control group was unusually low. If confirmed, this finding might have important implications, as the prevalence of antibiotic-resistant strains in children from all European countries is high and increasing, ranging from 12.4% to 23.5% (139). Adverse effects are commonly experienced by patients taking H. pylori eradication therapy and are reported by approximately 30% of patients taking triple therapy. The most common side effects are diarrhea, nausea and vomiting. The present study, again in contrast to almost all studies in adults, found no evidence of reduced adverse effects in the probiotic-supplemented group.
Summary and Recommendations
In summary, the evidence on usefulness of probiotics in the eradication of H. pylori is limited and questionable. More studies are warranted, especially in children, where only 1 RCT has been published. In adults, there is more solid evidence that probiotics may reduce the incidence of adverse effects of H. pylori eradication regimens. In conclusion, there is currently no evidence to recommend the use of probiotics in children with H. pylori.
PROBIOTICS IN PREVENTION OF FOOD ALLERGY
Potential for Probiotic Use
The hygiene hypothesis suggests that reduced microbial exposure during infancy and early childhood results in a slower postnatal maturation of the immune system and delay in the progression to an optimal balance between TH1 and TH2 immunity (140). Factors including sanitary conditions, maternal dietary intake, mode of delivery, antibiotic usage, gestational age and source of nutrition and factors intrinsic to the immune system have been associated with changes in the human intestinal ecosystem.
The TH1/TH2 imbalance is crucial to the clinical expression of allergy and asthma.
The intestinal microflora interacts with the mucosal immune system. It has been found that different strains of commensal bacteria vary in the cytokine response they generate. In balance, these bacteria can produce significant antiallergenic effects by intricate interactions inducing TH1 cytokines, such as interferon γ (141), T-regulatory cytokines, such as IL-10 and transforming growth factor β (142), and mucosal immunoglobulin A production (143).
The rationale for using probiotics in prevention and treatment of allergic disorders is based on the concept that appropriate microbial stimuli are required for normal early immunologic development. Several strains of Lactobacillus appear to modulate the phenotype and functions of human myeloid DCs: Lactobacillus-exposed mDCs up-regulated HLA-DR, CD83, CD40, CD80 and CD86 and secreted high levels of IL-12 and IL-18, but not IL-10. In similar in vitro studies, other strains of bacteria have shown differing responses. VSL#3 was studied with each individual strain providing distinct immunomodulatory effects. A marked anti-inflammatory effect was produced by bifidobacteria with an IL-10 induction by dendritic cells and consequent inhibition of TH1 activation with decreased interferon-γ production. These results underscore a potential role for Lactobacillus and VSL#3 in modulating immune responses (144-146).
The intestinal flora of atopic children has been found to differ from that of controls. Atopic subjects have more clostridia and tend to have fewer bifidobacteria than nonatopic subjects (147). Thus, there is indirect evidence that differences in the neonatal gut microflora may precede or coincide with the early development of atopy. This further suggests a crucial role for a balanced commensal gut microflora in the maturation of the early immune system.
In 1 randomized, double-blind, placebo-controlled trial (148), LGG was administered to 159 pregnant and lactating mothers who had at least 1 first-degree relative or partner with atopic eczema, allergic rhinitis or asthma. One hundred thirty-two mother-infant pairs (83%) were treated up to 6 months postnatally. The primary end point was chronic recurrent atopic eczema. Atopic eczema was found in 46 (35%) of 132 children at 2 years. The frequency of atopic eczema in the probiotic group was half that of the placebo group (23% vs 46%; RR, 0.51 [95% CI, 0.32-0.84]). The number needed to treat to prevent the onset of atopic eczema was 5 (95% CI, 3-16).
In a direct extension of this study, the 4-year follow-up examined the prevalence of atopic disease by questionnaire and a clinical examination. Fourteen of 53 children receiving lactobacillus had developed atopic eczema, compared with 25 of 54 receiving placebo (RR, 0.57 [95% CI, 0.33-0.97]). Skin prick test reactivity was the same in both groups: 10 of 50 children given lactobacillus compared with 9 of 50 given placebo. These results suggest that the preventive effect of LGG on atopic eczema extended beyond infancy (149). However, the results at 4 years should be interpreted with caution as only 67% (107/159) of randomized population was analyzed at this time.
Summary and Recommendations
Data are accumulating that are extremely encouraging in this area, and much more work is expected. Administration of LGG to pregnant and lactating mothers and their offspring for the first few months of life seems to be safe and may be effective in children at high risk for developing allergy Additional studies are needed to confirm the findings.
PROBIOTICS IN DIETETIC PRODUCTS FOR INFANTS
Potential for Probiotic Use
The lower incidence of gastrointestinal and other infections in breast-fed infants may, in part, be related to the difference in gut flora between breast-fed and artificially fed infants. Evidence is accumulating that gut flora modulates mucosal physiology, barrier function, systemic immunologic and inflammatory responses (150). In effect, the gut flora is thought to play a role in the overall health and well-being of the host (151).
On this basis, probiotics have been added to dietetic products for infants in an attempt to render their gut flora more similar to that of breast-fed babies. The most commonly used probiotics are bifidobacteria and lactobacilli, used singly or in combination. Several different strains and dosages have been used, but most are in the range of 1 × 106 to 1 × 1011 CFUs per gram of formula powder.
A recent position paper by the ESPGHAN Committee on Nutrition (152) reviewed the available evidence and concluded that there were limited data on safety and clinical effects and a lack of published evidence for long-term clinical benefit of formulas supplemented with probiotic bacteria.
THE ISSUE OF SAFETY
A major need in evaluating high-dose probiotic use in healthy infants is their safety and tolerance for extended periods. There is a paucity of relevant published information. A recent report focused on probiotic tolerance and safety in infants treated for 18 months (153). One hundred eighteen infants between 3 and 24 months of age (mean age, 7 months) were randomized to receive either a high-dose formula (B. lactis and S. thermophilus 1 × 107 CFUs per gram each), a low-dose formula (B. lactis and S. thermophilus 1 × 106 CFUs per gram) or a placebo. Mean formula consumption was similar in the 3 groups, and total viable bacteria intake was monitored weekly for each group. The number of episodes of loose stools, fever or vomiting did not significantly differ between the groups. However, there were significantly fewer reports of colic or irritability in both treatment groups compared to placebo. All infants showed normal growth, but the frequency of health care visits and antibiotic use (P < 0.001) was lower in both supplemented groups than in the placebo group.
It is of concern that there have been reports of bacteremia with some probiotic bacteria in high-risk populations (154). Endocarditis, pneumonia and meningitis have very rarely been reported in association with lactobacilli (154-158). A recent report from Finland indicates that an increase in the use of LGG in food has not increased the incidence of Lactobacillus bacteremia or the overall incidence of bacteremia from any organism (156). The available data suggest that the risk of infection with the probiotic lactobacilli or bifidobacteria is similar to risks with commensal strains.
Few probiotic strains have been tested rigorously in RCTs. The most extensively studied application and the best documented area of efficacy of probiotics is the treatment of acute infectious diarrhea. The final paragraphs of each previous section reflect our personal views on the current indications for use of probiotics. Clearly the effects of different probiotic microorganisms are not equivalent. Mechanism(s) of action are largely unknown. Acknowledging this difference among strains and characterizing the various mechanisms of action will allow more effective exploration of the potential benefits of probiotics.
Among the basic questions still unanswered are:
* Have we exhausted the choice of probiotics or are there more promising strains not yet identified?
* Can we genetically modify probiotics so as to achieve the desired profile?
* What are the best delivery vehicles?
* What do we know about the pharmacokinetic parameters?
* It seems obvious that a detailed investigation, strain by strain, of mechanisms of action and identification of specific clinical indications for use are needed. Many studies at the molecular and pathophysiological level as well as robust, well-designed clinical trials are clearly required. Labor-intensive as this effort may appear, it appears to us worth pursuing it, as we are indeed witnessing a revolution not unlike that seen 75 years ago, when Fleming's serendipitous observation began the antibiotic era.
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