Individualized management appears best for young febrile infants with positive urine culture

Admission to the hospital and treatment with antibiotics may not be necessary for young infants who have a positive urine culture and a negative urine dipstick. A recent study suggests these infants aged younger than 3 months are different from those who show leukocyturia and/or nitriuria.

To evaluate febrile infants younger than aged 3 months, current AAP recommendations call for obtaining both a urine dipstick and urine culture. The presence of leukocyturia and/or nitrituria in the urine dipstick strongly suggest the presence of a UTI. However, according to an article by Santiago Mintegi, MD, and colleagues from Spain, the value of urinalysis is controversial in young febrile infants.

The research team conducted a cross-sectional, descriptive study that included all febrile infants included in the prospective registry of infants aged younger than 3 months with fever of unknown origin (FUO) between September 2003 to August 2009. All infants had a urine culture. A positive result 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.

During the study, 1,376 febrile young infants were included in the registry. Urine culture was obtained for 774 patients, with a positive result in 246 infants. Of those 246 infants with positive culture, the urine dipstick was registered in 239 patients, with 187 (78.2%) infants having a positive result for leukocyturia and/or nitrituria.

According to findings, “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 urine culture,” the authors wrote.

The researchers concluded that infants matching the criteria of those in this study be managed in a different way as a function of the result of the urine dipstick results, because not all febrile infants with a positive urine culture need to be hospitalized, receive antibiotics or have 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,” the authors wrote.

Serious bacterial infections are found in 10% to 20% of febrile infants younger than 3 months of age, of which UTI is the most common. The gold standard to make the diagnosis of an UTI is urine culture.

John S. Bradley

Evaluation of the febrile infant in the first few months of life is always challenging, as the consequences of missing an invasive, serious bacterial infection is great in these immune-compromised hosts. Clinical presentations of relatively well-appearing infants can be misleading, making us much more dependent on laboratory tests to diagnose infections and treat appropriately. The authors have provided information on the diagnostic accuracy of a urine dipstick to help in both diagnosis of true infection, as well as in ruling-out infection in those with a positive urine culture and a negative dipstick test, particularly in the context of a normal serum procalcitonin.

Unfortunately, there are additional complicating factors present in this age group. First, febrile infants may have positive cultures (with 100,000 colonies/mL of urine) and no pyuria (first well-documented in Dallas 30 years ago with all urine samples collected by suprapubic aspiration): is this a true UTI, or bacteriuria with another cause for fever? Second, a high rate of urinary tract anatomic anomalies are first detected when these young infants present with a UTI (about 20% in some studies), increasing the risk of recurrent infections and UTI-associated bacteremia.

While helpful to quickly support a diagnosis of UTI (subsequently confirmed by culture, with further confirmation by an elevated serum procalcitonin concentration), a negative dipstick test, even with an initially low serum procalcitonin, may not successfully rule out true urinary tract pathology, as pointed out by the authors.

Until the natural history of bacteriuria in these infants is better defined, it may still be prudent to proceed with antibiotic treatment and ultrasound evaluation in this fragile population with positive urine cultures, including those with a negative dipstick test. Further evaluation of the role of procalcitonin in diagnosis of invasive UTI in very young infants may be more valuable for patient management than the dipstick test.

John S. Bradley, MD
Infectious Diseases in Children Editorial Board member

Disclosure: Dr. Bradley reports no relevant financial disclosures.

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