Diagnosis and Management of UTI in Febrile Infants Age 0–2 Months: Applicability of the AAP Guideline

“Action Statement 5: Febrile infants with UTIs should undergo renal and bladder ultrasonography (RBUS).”³

The AAP Guideline acknowledges that the RBUS is a poor screening test for the detection of genitourinary abnormalities in infants.³ The RBUS can be normal in infants with vesicoureteral reflux (VUR) or show nonspecific findings of unclear clinical significance.²⁸ In a prospective study of 220 infants <3 months old by Tsai et al, 9/39 infants (23%) with grade III-V VUR had normal RBUS.²⁹ Studies that included older infants have found a similar false-negative rate of 0%-40% for detecting grade IV-V VUR by RBUS.²⁸ Nonetheless, since a RBUS is safe and noninvasive, we feel that the benefits of screening for abnormalities such as hydronephrosis (that could indicate posterior urethral valves or ureteropelvic junction obstruction) outweigh the risks (eg, false positives, overdiagnosis, and cost) of performing a RBUS after a first-time UTI.

“Action Statement 6a: Voiding cystourethrography (VCUG) should not be performed routinely after the first febrile UTI; VCUG is indicated if RBUS reveals hydronephrosis, scarring, or other findings that would suggest either high-grade VUR or obstructive uropathy, as well as in other atypical or complex clinical circumstances.”³

“Action Statement 6b: Further evaluation should be conducted if there is a recurrence of febrile UTI.”³

The RBUS may be normal in infants with VUR. Therefore, the AAP’s recommendation to perform a VCUG only if the RBUS is abnormal or after a recurrent UTI concedes that there will be infants with VUR who are missed after the first UTI.³

The United Kingdom’s National Institute for Health and Care Excellence guideline recommends a VCUG for infants <6 months old with a bacteremic or non-E. coli UTI.³⁰ Whether high-grade VUR is more common in young infants with bacteremic UTIs than nonbacteremic UTIs remains inconclusive. In the Honkinen et al. study that included 87 infants <3 months old with bacteremic UTIs, the prevalence of grade IV-V VUR (10%) and obstruction (7%) was higher than that of the 88 nonbacteremic infants (2% grade IV-V VUR and 2% with obstruction). In the multicenter study of 251 infants <3 months old with bacteremic UTIs, the prevalence of grade IV-V VUR was 12.1%.³¹ This is higher than that of the nonbacteremic infants in Honkinen et al.’s study³² but more similar to the prevalence of grade IV-V VUR found in Tsai et al. (8.2%) and Ismaili et al.’s (7.0%) studies of UTIs in general.^29,33

There does appear to be a higher prevalence of urinary tract abnormalities in young infants with non-E. coli vs E. coli UTIs.^31,32,34,35 The odds of an abnormal VCUG was 8.0 (95% CI: 2.3-28) times higher for non-E. coli than E. coli UTIs in the study of 251 bacteremic infants.³¹ In a study of 122 infants <3 months old, the odds of grade III-V VUR was 10 (95% CI 2.6-41) times higher for non-E. coli than E. coli UTIs.³⁵

However, the need for early detection of VUR is controversial, and VCUGs are invasive, involve ionizing radiation, and may require sedation. Two recent trials (one which included only children with VUR and another in which 42% of subjects had VUR) demonstrated a modest effect of prophylactic antibiotics in preventing recurrent UTIs (>5,000 doses of antibiotics needed to prevent one UTI recurrence), but the effect size did not differ by the presence or degree of VUR, and neither demonstrated any benefit in reducing future renal scarring.^{36, 37} The benefit of surgical interventions for VUR also remains unclear, though studies are limited.³⁸ Overall, there is no evidence suggesting that infants <2 months old require more vigilance for VUR detection than the 2-24 month age group.