Should the Absence of Urinary Nitrite Influence Empiric Antibiotics for Urinary Tract Infection in Young Children?

OBJECTIVES: Screening for urinary tract infection (UTI) includes urinary nitrite testing by dipstick urinalysis. Gram-negative enteric organisms produce urinary nitrite and represent the most common uropathogens. Enterococcus, a less common uropathogen, does not produce nitrite and has a unique antibiotic resistance pattern. Whether to adjust empiric antibiotics in the absence of urinary nitrite has not been established. Our primary objective was to determine prevalence of enterococcal UTI among young children with a nitrite negative urinalysis.

METHODS: A retrospective study of children aged less than 2 years evaluated in the emergency department for possible UTI and had a paired urinalysis and urine culture was performed. Urinary tract infection was defined by catheterized culture yielding greater than or equal to 50,000 colony-forming units per milliliter of a single uropathogen. Prevalence of uropathogens among nitrite negative samples was studied.

RESULTS: A total of 7599 children were studied. Median (interquartile range) age was 5.6 (2.3-11.2) months, and 57% were female. Prevalence of UTI was 8.1%. Enterococcus was the uropathogen in 2.1% of UTIs, and all cases had negative dipstick nitrite. Among nitrite negative UTIs, 95.6% of uropathogens were gram-negative and only 3.2% (confidence interval, 1.8%-5.3%) were enterococcus. None of the 200 UTIs with positive nitrite yielded enterococcus (upper confidence interval, 1.4%). Among children with positive leukocyte esterase and negative nitrite, only 0.7% of cases had enterococcal UTI.

CONCLUSIONS: Only 3% of nitrite negative UTIs were caused by enterococcus. Given the low prevalence of enterococcal UTI, the absence of dipstick nitrite should not affect routine empiric antibiotic choice for presumptive UTI in young children.