PEDIATRIC SPECIAL SECTION
IN THE LITERATURE
Utilize Clinical and Demographic Factors to Diagnose UTIs in Young Febrile Infants
Review by Sara E. Gardner, MD
Zorc JJ, Levine DA, Platt SL, et al. Clinical and demographic factors associated with urinary tract infections in young febrile infants. Pediatrics. 2000;116(3):644-648.
UTI is a common cause of serious bacterial infection in the febrile infant <60 days of age. Standard urinalysis and urine dipstick techniques, commonly used to diagnose UTI, have relatively low sensitivity increasing the possibility of a missed diagnosis. An accurate initial diagnosis is critical in this age group for whom complications from UTI include bacteremia and renal scarring.
To describe the demographic and clinical factors associated with UTI in infants ≤60 days of age with fever, these authors conducted a prospective cross sectional study from October 1999 to March 2001. Patients were enrolled at eight different institutions after presentation to an emergency department. One-thousand-twenty-five patients age 60 days or younger (mean age 35.5 days, 60.5% male) were enrolled with either reported or documented fever >38. Routine testing for all children included respiratory syncytial virus (RSV) sampling and bladder catheterization or suprapubic aspiration for urinalysis and culture.
A positive urinalysis was defined as a trace or greater result for leukocyte esterase and/or nitrite on dipstick or greater than or equal to five WBCs per high power field (hpf) on urine microscopy. UTI was defined as growth of a single pathogen of ≥1,000 colony forming units (cfu)/mL for urine cultures obtained by suprapubic catheterization, ≥50,000 cfu/mL from a catheterized specimen, or ≥10,000 cfu/ml from a catheterized specimen with a positive urinalysis.
Of the patients enrolled in the study, 92 were found to have UTI by these diagnostic criteria. Using the chi-squared test and calculated odds ratios with 95% confidence intervals, uncircumcised male (OR: 10.4; 95% CI: 4.7-31.4) and maximum temperature of ≥39º C (OR: 2.4 per degree C; 95% CI: 1.5-3.6) were found to be statistically significant variables for predicting UTI. These risk factors remained statistically significant after multivariable analysis controlling for other factors.
Interestingly of the above 92 patients diagnosed with UTI, 85 grew ≥50,000 cfu of a single pathogen, but six (8%) grew 10,000-49,000 cfu with a positive UA based on the study criteria. Zorc, et al. included these patients with >10,000 cfu and >5 WBC/hpf in this study despite previous studies that have established a definition of positive urinalysis to be ≥10 WBC/hpf. Zorc, et al. acknowledge the conservative definition applied in their current study, but assert that the overall results of the study would have been similar had 10,000 or 50,000 cfu/mL thresholds been chosen. To support this assertion, Zorc, et al. retrospectively applied enhanced urinalysis, a sensitive form of urinalysis including hemocytometric cell count and gram stain described by Hoberman, et al. to study patients with low bacteria counts. Based on Hoberman’s study, enhanced urinalysis can differentiate acute infection from asymptomatic bacteriuria in patients with bacterial growth between 10,000 to 50,000 cfu/mL.
Another significant limitation of this study was failure to enroll one-third of eligible patients to the study. In addition, the authors note that missed patients had a lower rate of UTI compared with enrolled patients.
Although this study design prohibits generalization to patient care areas outside the emergency department, the findings can assist the hospitalist in the evaluation of the febrile infant during RSV season and potentially guide decisions regarding empiric antibiotic therapy as part of evaluations to diagnose or exclude serious bacterial infection. Additionally, this study raises the question of need for better methods of urinalysis for febrile, uncircumcised male infants.