The rates of positive cultures and distribution of pathogens were similar in infants who were premature (gestational age <37 weeks) versus term or who were delivered at home versus in the hospital (with the possible exception of more Pseudomonas spp. isolated from infants with home vs. facility-based deliveries; 4/33 vs. 0/50, P = 0.01).
Notably, the proportions of S. aureus positive cultures stratified by initial clinical diagnostic category were the following: 13/305 (4.3%) (no diagnosis of infection), 13/381 (3.4%) (sepsis diagnosis), 2/33 (6.1%) (focal infection) and 8/63 (12.7%) (focal plus systemic) (P = 0.012). These results point to a higher proportion of S. aureus isolates in the focal plus systemic infection group.
Antimicrobial Susceptibility Results
Since the study sites used different panels of antibiotics for susceptibility testing, the number of isolates tested for different antimicrobial agents varied. Among the Gram-positive isolates, S. aureus was most commonly tested (n = 45). Most S. aureus isolates were resistant to penicillin (88%, 22/25) and cotrimoxazole (66%, 21/32). Lower levels of resistance among the S. aureus isolates were found for erythromycin (19%, 8/43) and ciprofloxacin (14%, 3/22). Methicillin/oxacillin resistance was identified in 11% of the S. aureus isolates (4/37).
The susceptibility patterns of Gram-negative bacteria for which there were 2 or more isolates are presented in Table 4. Nearly all isolates were resistant to ampicillin or amoxicillin, first generation cephalosporins, chloramphenicol and cotrimoxazole. Resistance to second and third generation cephalosporins occurred in more than half of isolates. Similarly, a moderate proportion of isolates were resistant to gentamicin (17/39, 43%) and ciprofloxacin (11/31, 35%).
Clinical Outcomes of Infants With Bacteremia
The choice of empirical antimicrobial therapy varied from site to site. For those sites that systematically documented which antibiotics were used, the clinicians involved generally modified their choice of treatment after receiving the blood culture results. Broad-spectrum second and third generation cephalosporins with or without an aminoglycoside were used for Gram-negative infections while third generation cephalosporins or antistaphylococcal penicillins were used for treatment of S. aureus. Mortality rates were similar in admitted infants with positive (5/71, 7.0%) and negative blood cultures (42/557, 7.5%) (Table 2). Mortality rates were higher in the 0–6-day-old than the 7–59-day-old infants (38/383, 9.9% and 12/272, 4.4%, respectively). Excluding all infants whose blood culture isolate was S. aureus, in whom mortality was 2.8% (1/36), there still was no apparent association between bacteremia and mortality in either 0–6-day-old infants [3/20 (15%) vs. 34/343 (9.9%), P = 0.46] or in 7–59-day-old infants [1/19 (5.3%) vs. 11/241 (4.6%), P = 0.89).
Of the 12 bacteremic infants who were not admitted, there were 9 for whom day 3 outcome data were available. Six had improved, 2 had not improved and 1 was classified as sick and requiring urgent attention.
This multi-site study, which included 7 sites in 6 countries, enrolled a large number of young infants brought to health facilities for evaluation of a broad range of illnesses. Among infants requiring urgent hospital management, the main organisms isolated were S. aureus and several different species of Gram-negative bacilli. Notably the distribution of Gram-negative bacilli and Gram-positive organisms was similar between the 2 age groups: newborns 0–6 days and infants aged 7–59 days. This study was designed to emulate community sites with a wide spectrum of milder illnesses, not only infections, but also illnesses such as jaundice as an isolated clinical sign and birth asphyxia, which have a low risk of bacterial infection. Even in children with a high likelihood of bacterial infection, the isolation rate was relatively low (~11%). Notably, a large summary of blood culture data from a tertiary care center in London found that 12% of 8904 cultures taken from neonates with suspected sepsis were positive14 and a summary of bacteremia data from hospitalized children in Kilifi, Kenya, found that 12.8% of infants <60 days old that had blood cultures yielded pathogens.15 Similar results were found at the same site in a study of community-acquired bacteremia in infants <2 months old with possible serious bacterial infection which found a prevalence of 9%.16 These are remarkably similar to our isolation rate. However, it is possible that pre-treatment with antibiotics occurred in some of our patients before presentation to the study center and this might have reduced the rate of blood culture positivity.
Only slightly more than half of the infants who were admitted had blood cultures done even though this was supposed to have been done as part of the study protocol. In many cases, this was due to a decision by the study pediatrician that doing a blood culture was not necessary based on their admitting clinical diagnosis, which included conditions that were not due to infection such as severe jaundice in the absence of other clinical signs. Although these technically represented protocol violations, it is unlikely that these infants would have had positive cultures since many were admitted for management of diseases unlikely to be complicated by serious bacterial infections.
There are relatively few other studies from developing countries that have studied large numbers of neonates and infants with community-acquired bacteremia. A review of 63 studies, including 13 that focused on community-acquired infections, found that Klebsiella spp., E. coli and S. aureus were the most common isolates in the first week of life while S. aureus, GBS, Streptococcus pneumoniae and nontyphoidal Salmonella spp. were the most frequent isolates in infants ranging from week 2 of life to 90 days.17 A previous WHO-supported study found that Gram-positive organisms, especially S. aureus, S. pneumoniae and S. pyogenes were present in 61% of blood culture isolates (n = 102).18 This study found Gram-negative bacilli in 39% of young infants that cultures performed, with E. coli and Salmonella spp., the most commonly encountered Gram-negative isolates. A community-based study in Mirzapur, Bangladesh found a mix of Gram-positive isolates with S. aureus predominating and Gram-negative isolates in neonates.11 Thus, all of these studies, many of which are included in the aforementioned review, found a similar range of pathogens to what we encountered in our study. The consistent identification of S. aureus as a possible pathogen in young infants might be secondary to horizontal transmission in facility-based deliveries and person-to-person transmission in home deliveries resulting in colonization and infection. Alternatively, S. aureus skin carriage coupled with inadequate site sterilization might have resulted in the inoculation of bacteria into the blood culture bottles or some of the positive cultures resulted from transient S. aureus bacteremia, which was not clinically significant. Consequently, the role of S. aureus as a true pathogen remains unclear.
One of the striking findings of our study was the paucity of Gram-positive organisms other than S. aureus, especially GBS. The latter is the most common Gram-positive pathogen reported for this age group in developed countries.19 In contrast, it was rarely found in the previous Young Infant Study or the Mirzapur community-based study.11,18 Our findings are thus consistent with several other studies that have shown a low prevalence of GBS20; this pathogen may be less commonly encountered in developing relative to resource-rich countries due to a lower prevalence of maternal and neonatal colonization or colonization with less virulent strains which are less likely to cause invasive disease.17,21 In developed countries, GBS became a dominant pathogen only in the 1960s.22 Traditionally, the main species of streptococcus was group A, both as a pathogen for puerperal sepsis and for neonatal infections.23 Improvements in hygiene may have contributed to this shift. However, it is also possible that newborns with sepsis due to GBS present as critically ill, especially in early onset neonatal sepsis, and they are at substantial risk of early mortality.24 Since we excluded newborns requiring immediate cardiopulmonary resuscitation, some more critically ill newborns might have had early onset GBS sepsis. Furthermore, some neonates with GBS sepsis might have died before reaching the health facility, thus potentially explaining the absence of early and late onset GBS bacteremia in our study.
Resistance to inexpensive, widely used antibiotics (eg, cotrimoxazole, penicillin and ampicillin/amoxicillin) was common. These findings are consistent with a recent review which found that nearly half of S. aureus isolates were resistant to cotrimoxazole and a substantial proportion of E. coli isolates were resistant to cotrimoxazole and ampicillin.25 A worrisome finding was the presence of methicillin resistance in 11% of S. aureus isolates. In the community-based Bangladesh study, 10% (1/10) of S. aureus isolates were oxacillin resistant.11 Limited data from other studies of community-acquired bacteremia suggest that methicillin-resistant S. aureus is uncommon.25 However, susceptibility results were only available for 5 isolates in that review in contrast to our study, which included methicillin resistance testing for 37 isolates. In contrast, a recent review, which highlighted the paucity of data on antimicrobial resistance patterns among neonatal sepsis pathogens, suggests that some locations in sub-Saharan Africa may be encountering increasing problems with methicillin-resistant S. aureus, based on evidence of ceftriaxone resistance.26
An additional finding of concern in our study was the presence of moderate to high levels of resistance of Gram-negative isolates to a number of different antimicrobial agents, including later generation cephalosporins, gentamicin and ciprofloxacin. Since the study eligibility criteria were designed to avoid inclusion of recently hospitalized newborns and thus exposure to nosocomial pathogens, the presence of multi-drug resistance in community isolates is of great concern. In view of these resistance patterns, less intensive community-based treatment regimens for newborn sepsis, which rely on fewer injections with gentamicin and oral amoxicillin, may not provide adequate antimicrobial treatment coverage.27
There are a number of limitations that merit comment. There were many infants referred for hospitalization who did not have blood cultures performed and thus we may have missed some episodes of bacteremia. The protocol excluded critically ill infants in need of immediate resuscitation, some of whom may have had infections that we missed. We do not have long-term outcome data for the infants who participated in the study. Since susceptibility testing was not done routinely at all sites and there is likely to be regional variation in resistance patterns, the value of the study to guide selection of antibiotics for treatment of sepsis is limited.
Given the broad array of different pathogens identified in newborns and young infants with community-acquired bacteremia, the high prevalence of resistance to commonly used front-line antibiotics and a suggestion of moderate levels of resistance to newer, more expensive antimicrobial agents, there is a need for tertiary care health facilities in resource-poor countries to have the capacity to perform blood cultures, identify pathogens and their susceptibility profiles. Improved microbiological capacity and regional surveillance of resistance patterns will help improve the management of community-acquired and hospital-acquired neonatal sepsis. At the primary health care level, the choice of antibiotic regimens for neonatal sepsis needs to be guided by local resistance data, when available. In addition, therapy should consider the addition of antistaphylococcal coverage, especially when signs of skin or soft tissue infection such as omphalitis are present.28
This manuscript is dedicated to Durrane Thaver, who played a central role in the early microbiological analyses and who sadly died a premature death.
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APPENDIX 1. Laboratory Methods and Quality Control Systems
APPENDIX 2. Members of the YICSS Group
Study sites: Bangladesh: Investigators: A.K. Azad Chowdhury (PI), Samir K. Saha, A. S.M. Nawshad Uddin Ahmed, Md. Monir Hossain; Study physicians: Nazmun Nahar; Nurses: Amala Baidya, Mahmuda Parul; Laboratory personnel: Maksuda Islam, Tania Nasreen; Data management: Md. Rezaur Rahaman; Bolivia: Clinical investigators: Eduardo Mazzi (co-PI), Andrés Bartos (co-PI); Study physicians: Teresa Villagomez, Pablo Mattos; Manuel Pantoja Ludueña, Remedios Zumarán; Study nurses: Irma Quispe, Willy Tarqui, Lourdes Checa, Claudia Canqui; Data management: Erick Dueñas, Omar Vargas; Ghana: Clinical investigators: Emmanuel Addo Yobo (PI), Kojo Yeboah-Antwi, Yaw Adu-Sarkodie; Study physicians: G. Plange-Rhule, Osei Akoto; Laboratory: M. Lartey; Data management: Henrietta Akpene; India, Chandigarh: Clinical investigators: Anil Narang (PI), Praveen Kumar, Rupinder Narang; Study physicians: Prasad Muley, Satish Misra; Nurses: Tapasaya, Sanjay Rani; Laboratory: Pallab Ray, Tamanna Gaur; Data management: Vishal Kanojia, Ajay Dogra; India, Delhi: Clinical investigators: Ashok K. Deorari (PI), Harish Chellani, M. S. Prasad; Study physician: A. Satyavani; Nurses: Jyoti, Raji John; Laboratory: Arti Kapil; Data management: Sanjeev Negi, Narinder Singhal; Pakistan: Clinical investigators: Anita K. M. Zaidi (PI), Zulfiqar A. Bhutta, Shiyam Sunder; Study physicians: Shazia Sultana, Shazia Azeem, Razzaq Lasi, Farrukh Abbasi; Lady Health Visitors: Razia Sultana, Nasira A. Jabbar; Laboratory: Rumina Hasan; Data management: Arjumand Rizvi; Durrane Thaver*; South Africa: Clinical investigators: Prakash M. Jeena (PI), Miriam Adhikari; Nurse: Sister Mojaphelo; Laboratory: Wim Sturm; Data management: Precious Sikhakhane.
Study advisors: Rajiv Bahl, Kim Mulholland, Vinod Paul, Eric Simoes, Jelka Zupan.
Study Coordination: Gary L. Darmstadt, Global Development Division, Bill and Melinda Gates Foundation, Seattle, WA, USA.
Davidson H. Hamer, Center for Global Health and Development, Boston University, Boston, MA, USA.
Martin W. Weber, World Health Organization, Geneva, Switzerland.
Data Management: Philip Greenwood, Claudine Chionh, Murdoch Children’s Research Institute.
Statistical Analysis: John B. Carlin, Murdoch Children’s Research Institute and University of Melbourne, Melbourne, Australia.
Keywords:© 2015 by Lippincott Williams & Wilkins, Inc.
Neonatal sepsis; infant; neonate; bacteremia; Staphylococcus aureus