Diagnosing and Treating UTI in the First 2 Months of Life

An outstanding session on "Controversies in the Diagnosis and Management of Urinary Tract Infection in Infants < 2 Months Old" was held at the Pediatric Academic Societies (PAS) 2021 Virtual Event.

The panel noted that there is an American Academy of Pediatrics Clinical Practice Guideline on the diagnosis and treatment of UTI among children 2-24 months, reaffirmed in 2016. But practitioners also have questions about the approach to febrile infants younger than 2 months and how the presence of UTI may influence diagnostic and therapeutic choices. Answering some of those questions for infants 0-2 months was the purpose of this session, focusing in particular on making the diagnosis, need for testing beyond urine, and recommendations for treatment.

Diagnosing UTI in Newborns 0-2 Months

The first question was whether the diagnosis of UTI in infants 0-2 months differs from the approaches in the guideline, which recommends that UTI diagnosis be made only when you have both a positive urine culture and evidence of infection on the urinalysis, either pyuria (> 5 WBC/hpf on centrifuged microscopy) or bacteriuria (positive leukocyte esterase or bacterial nitrite).

Dr Tom Newman, of the Stanford Department of Pediatrics, commented that it can be difficult to determine the "gold standard" for the diagnosis of UTI in infants younger than 2 months of age. Instead, the clinician is dealing with degrees of probability and will have to accept some degree of uncertainty.

For example, among infants younger than 2 months, a positive urine culture without pyuria may not identify a true UTI but might instead just be identifying asymptomatic bacteriuria. One approach that researchers have used to assess the value of a urinalysis in diagnosing UTI comes from evaluations of infants 0-3 months with UTI and bacteremia from the same organism. Urinalysis performed well in that population to identify UTI with 98% sensitivity, primarily driven by leukocyte esterase or the presence of pyuria (both with sensitivities of 96% or greater).

Catheter or Urine Bag?

A second question concerns urine specimen collection — whether it should be obtained by catheter or whether a noninvasive (bagged) specimen is sufficient. Newman suggests obtaining a catheterized specimen for culture from any febrile infant under 2 months of age who is ill-appearing enough for you to consider admission to the hospital. For well-appearing febrile infants, data show that bagged urine and catheter specimens perform similarly in identifying UTI among young infants when tested in community practices, suggesting that either collection method is acceptable.

Pyuria with leukocyte esterase is the strongest combination for predicting a true UTI, and several panelists suggested that it would be reasonable to treat these children presumptively without the need for a urine culture. However, urine samples obtained by bag method should not be used for culture. Culture should be obtained by catheterization.

Is Lumbar Puncture Necessary?

The third question was whether lumbar puncture should be routinely done in very young infants with UTI. Dr Paul Aaronson, from Yale University, reviewed several studies that evaluated the risk for meningitis in this population, with and without UTI.

First, data from 12 studies demonstrated that meningitis occurred in 0.9% of febrile infants 0-2 months old (1.2% among those younger than 1 month and 0.4% among those 1-2 months old). Other data show a prevalence of meningitis in young infants of about 0.25%-0.68% (depending on subpopulation), regardless of whether UTI is present, suggesting that the risk for meningitis is unrelated to the presence of UTI. Of course, clinicians operate under the concern that they will "miss" meningitis if they evaluate and treat only for UTI, but data from 2015 and 2020 demonstrated that missing meningitis in infants evaluated only for UTI is indeed very rare.

Therefore, Aaronson's assessment was that febrile infants aged 29-60 days who are well-appearing and with normal inflammatory markers (procalcitonin < 0.5 ng/mL) could avoid a lumbar puncture. Clinicians should consider obtaining a lumbar puncture for a febrile infant aged 21-28 days, especially if inflammatory markers are elevated. Of importance, all of the authors view newborn infants from day 1 to day 21 of life (and even those aged 21-28 days) as a "different group" when it comes to the risk for both UTI and accompanying bacteremia and meningitis, so one take-home message is that practitioners have leeway for application of these data and diagnostic approaches primarily during the second month of life only.

Duration of Intravenous Antibiotics?

The final question was related to duration of intravenous antibiotic therapy for infant UTI. Dr Alan Schroeder, also from Stanford University, began by asking why clinicians feel that they should treat UTI in young infants with prolonged courses of IV antibiotics. Are they concerned about recurrence? Are they concerned that the infants' enteral absorption is insufficient for oral therapy?

We've seen a large drop in the percentage of young infants treated intravenously for 4 or more days for UTI, from 50% in 2005 to 19% as of 2015. Shortened duration of IV antibiotics before transition to oral therapy for UTI is supported by randomized data (Bouissou et al, 2008; Bocquet et al, 2012). In a 2016 study of 251 children with bacteremia and UTI, evaluation of the duration of IV therapy revealed that none of the patients experienced a relapsed UTI with bacteremia, and only six had relapsed UTI, unrelated to duration of IV therapy. Schroeder, therefore, made the following recommendations for well-appearing but febrile infants being treated for UTI. First, infants aged 0-1 month should be treated with IV therapy for 1-2 days awaiting culture results and — when urine cultures grow — sensitivities. For infants aged 1-2 months who are well-appearing and generally healthy, either oral or intramuscular treatment for 1-2 days awaiting culture results would be appropriate.

In conclusion, during the past decade, more and more data support applying the same approaches in the clinical practice guideline for infants 2-24 months to well-appearing but febrile infants in the second month of life. It is less clear whether the approaches are as sound for the very youngest newborns in the first month of life.

William T. Basco, Jr, MD, MS, is a professor of pediatrics at the Medical University of South Carolina and director of the Division of General Pediatrics. He is an active health services researcher and has published more than 60 manuscripts in the peer-reviewed literature.

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