Serious bacterial infections (SBIs) are found in 10% to 20% of febrile infants younger than 3 months of age,1 urinary tract infections (UTI) being the most common SBI.2
The gold standard to make the diagnosis of an UTI is urine culture (UCx).3
Recommendations for the evaluation of febrile infants younger than 3 months of age include obtaining both a urinalysis (eg, Urine Dipstick, UD) and UCx to screen for UTIs. Thus, when evaluating a young febrile infant, the presence of leukocyturia and/or nitrituria in the UD strongly suggest the diagnosis of an UTI.
However, the value of urinalysis remains controversial in febrile young infants.4,5 In this way, it has been stated recently that urinalysis is not reliable for the detection of UTI in well-appearing febrile infants when compared with the results of UCx.6 On the other hand, some authors consider that diagnosing an UTI without leukocyturia may not be correct and others classify the patients with a positive UCx in a different way depending on the detection or not of leukocyturia.7
Our objective was to analyze the characteristics of the patients with a positive UCx obtained in the Pediatric Emergency Department (PED) when they are evaluated for fever without a source (FWS), comparing the subgroups with positive and negative UD results.
PATIENTS AND METHODS
A prospective registry of infants of less than 3 months with FWS was established in 2001 at our PED. Electronic medical records of the PED are reviewed to collect the data of the included patients. The patient's final charts on discharge are reviewed when the infant has been admitted. If the infant is not admitted to hospital, a follow-up phone call is made in the following month by resident doctors. The hospital database is checked to determine whether there have been any unscheduled emergency visits after the initial discharge.
We conducted a cross-sectional, descriptive study including all febrile infants included in the registry since September 2003 to August 2009 and for whom an UCx had been obtained. Positive UCx was considered with a growth of more than 10,000 colony-forming units/mm3 of a single bacterial pathogen in a urine sample collected by bladder catheterization.
Management in the PED: Until 2008, UCx obtained by bladder catheterization was performed only if the urine sample obtained by bag collection showed leukocyturia and/or nitrituria. Since then, we have been recommended that UCx (bladder catheterization) to be obtained in all febrile infants.
Statistical Program for the Social Sciences version 15 (SPSS 15, Chicago, IL) was used for all statistical calculations. Data are expressed as the mean and standard deviation for quantitative variables, and numbers and percentages for categorical variables. Continuous data were compared using the Student t test, whereas categorical data were examined using the χ2 or the Fisher exact test probability tests. Statistical significance was defined as P ≤ 0.05.
This study was approved by the Research Committee of the PED.
During the study period, 1376 febrile young infants were included in the registry. Of these, UCx was obtained in 774, and the result was positive in 246. Among this subset, the UD result was registered in 239 patients and, of these, 187 (78.2%) were positive for leukocyturia and/or nitrituria (positive UD).
Groups with positive and negative UDs were similar in terms of sex or temperature. Among infants with normal UD, 20 were younger than 28 days of age (28.5% of this age group, vs. 32/169, 18.9%, of those older, P = 0.12).
When compared with patients with positive dipstick results, patients without leukocyturia and/or nitrituria showed significant differences in relation to the blood biomarkers and the bacteria isolated in the UCx (Table 1).
No significant differences were found in these parameters between patients with a positive UCx and negative UD and those diagnosed with FWS and a negative UCx (Table, Supplemental Digital Content 1, http://links.lww.com/INF/A905).
Of the 52 febrile young infants with negative UD, 26 (50%) were initially managed as outpatients (all, except one, without antibiotic). Management of these patients trended to be more aggressive in the initial phases of the registry (admission and intravenous antibiotic, mainly). Among those 26 infants, 18 were re-evaluated at the PED when the UCx result was received. All of them were well appearing, and just 2 were admitted to a ward with antibiotic. The other 16 continued to be managed as outpatients (only 4 with antibiotics and a third of them became afebrile within the first 24 hours after visiting the PED). The 8 infants who were not re-evaluated at the PED were managed by their primary care pediatrician.
Our study shows that febrile young infants with a positive UCx have differences related to the presence of leukocyturia and/or nitrituria in the urinalysis. These differences are found in the blood biomarkers and the bacteria isolated in the UCx. Febrile young infants with a positive UCx and leukocyturia and/or nitrituria were more often found to have abnormal WBC, absolute neutrophil count, and levels of C-reactive protein and procalcitonin, as well as Escherichia coli more often being isolated, than in those with a positive UCx and a negative UD.
Febrile infants with a positive UCx usually receive antibiotics and, following the American Academy of Pediatrics recommendations,8 most of them under 2 months of age are admitted to hospital.
It has been suggested that UCx should be carried out for infants with a suspected UTI due to the lower sensitivity of the UD in infants.9,10 Recently, other authors have stated that urinalysis is less reliable for the detection of UTIs in well-appearing febrile infants than the results of UCx.6 However, investigators in several studies in large cohorts of infants younger than 2 years of age with undiagnosed fever or symptoms of an UTI have found negative predictive values greater than 98% despite sensitivities of 79%.11,12
It is sometimes recommended that an UCx is obtained in all febrile young infants to identify all the infants with a positive UCx and not to miss any infant with an UTI. However, other authors maintain that urinalysis alone in concentrated urine is adequate to rule out an UTI in certain populations.13
Our data suggest that febrile infants under 3 months of age with a positive UCx can be managed in a different way as a function of the result of the UD. Probably, according to our data, not all febrile infants with a positive UCx need to be hospitalized, receive Ab, or studies like voiding cistography. We suggest that the management should be individualized, as at least some of these infants may have an asymptomatic bacteriuria or contaminated catheter specimen.4 Although the data are not collected in our registry, nearly 100% of young males in the Basque Country are not circumcised, and this may facilitate the contamination of the sample. This idea is supported by the fact that, in our series, abnormal values for biomarkers in febrile infants with a positive UCx, usually associated with an SBI, are more uncommon in infants with negative UD. The blood biomarkers in patients with a positive UCx and negative UD were significantly different from those in the group of patients with a positive UCx and positive UD and were similar to the group of patients with a negative UCx and diagnosed with FWS. Moreover, bacteria isolated in the UCx were different in both groups. It is also worth noting that a considerable number of febrile infants without leukocyturia and/or nitrituria, when contacted by telephone when positive UCx results arrived, were reported to be well and afebrile without antibiotic treatment.
This study has several limitations. A prospective study would have allowed greater thoroughness in the collection of data. However, data were extracted from a prospective registry which provides good quality data. Second, it was not a multicenter study, thus it may be difficult to extrapolate the results to other populations. Third, DMSA scans were not carried out on the studied population and such data would have complemented the analysis carried out in our study.
We can confirm that positive UCx is a common finding in the assessment of a young infant with FWS. A considerable proportion of patients with positive UCx do not show up as positive for leukocyturia and/or nitrituria in the UD test, while abnormal complete blood cell count, and levels of C-reactive protein and procalcitonin are more common in patients with leukocyturia and/or nitrituria. We believe that febrile young infants less than 3 months old with positive UCx and negative UD are different from those who show leukocyturia and/or nitrituria and admission to the ward and antibiotic treatment may not be necessary for all such patients.
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