Prevalence of UTI With Bronchiolitis

Written by Clay Smith

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When UTI was defined as a positive urine culture plus abnormal UA, the prevalence of concomitant UTI in febrile infants with bronchiolitis was 0.8% - below the usual testing threshold.

Why does this matter?
Studies have shown that febrile infants <3months with bronchiolitis may also have concomitant UTI in 3.3%.  But how was “UTI” defined in these studies?  Most defined it as having a positive urine culture.  However, a positive culture in the absence of an abnormal UA (pyuria or nitrite) may represent asymptomatic bacteriuria or contamination.  In 2011, the AAP revised the definition of UTI to, “include both an abnormal UA result (pyuria or bacteriuria) and a positive urine culture (>50000 cfu/mL).”  How does this definition affect the prevalence of concomitant UTI with bronchiolitis?

UTI + bronchiolitis = bad luck
This was a systematic review of 18 studies looking at the prevalence of concomitant UTI in infants presenting with bronchiolitis.  When looking at all 18, the prevalence was 3.1%.  However, when only the seven studies with both positive UA (pyuria or nitrite) and urine culture were included, the prevalence was 0.8%.  That’s 125 infants needed to test to find one UTI.  The AAP does not recommend testing for UTI unless the pretest probability of disease is 1-3%.  UTICalc can help determine pretest probability.  When children <90 days were excluded, the prevalence of UA+/culture+ UTI was 0.5%.  The study was limited in that the definition of UTI varied across centers, as did the definition of bronchiolitis (some RSV+ only, some clinical).  It also included a wide range of ages, from <60 days to 36 months or older.  This study changes my practice.  Previously, in febrile children with bronchiolitis, I was apt to ignore the bronchiolitis as the source of fever and check a urine anyway.  Now, if they clearly have bronchiolitis, I probably won’t check a UA.  However, this does not change the fact that children who lack other localizing symptoms for fever still need a urinalysis/urine culture if the pretest probability for UTI exceeds the threshold of ~2%.

Source
Association of Diagnostic Criteria With Urinary Tract Infection Prevalence in Bronchiolitis: A Systematic Review and Meta-analysis.  JAMA Pediatr. 2019 Jan 28. doi: 10.1001/jamapediatrics.2018.5091. [Epub ahead of print]

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