This study analysed the association between a positive nitrite dipstick test and an invasive bacterial infection (IBI) in infants younger than 90 days of age with fever without source (FWS).
We performed a secondary analysis of data from a prospective multicentre study of infants up to 90 days of age with FWS undergoing care in 19 paediatric EDs between October 2011 and September 2013. IBI was defined as a positive blood or cerebrospinal fluid culture.
The dipstick urinalysis was positive for nitrite or leucocyte esterase in 766 (22.5%) of the 3401 infants we studied and 270 (35.2%) had a dipstick test that was just positive for nitrite. Overall, 107 were diagnosed with an IBI (3.1%). The IBI prevalence was 2.2% among patients with a normal urine dipstick, 4.4% if they had positive leucocyte esterase test results, 8.3% where the nitrite test was positive and 10.6% when both tests were positive. After multivariate analysis, a positive nitrite test remained an independent risk factor for IBI (odds ratio 2.7, 95% confidence interval 1.4-4.9).
In infants under 90 days of age with FWS, a positive nitrite urine dipstick test was an independent risk factor for IBI.

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