Identifying a serious bacterial infection in children less than 60 days of age is easier said than done. One wants to get antibiotics started when appropriate but on the other hand, one doesn’t want to overuse antibiotics if one doesn’t need to. So what clues might we have that bacteria are lurking somewhere in an infant’s body? One major clue might lie in the simply urinalysis (UA)—but just how sensitive and specific is a urinalysis for identifying a bacterial urinary tract infection (UTI). Tzimenatos et al. (10.1542/peds.2017-3068) studied the accuracy of the urinalysis for identifying a UTI in a new study derived as a secondary analysis of a larger prospective multicenter study involving 26 emergency departments who are part of the Pediatric Emergency Care Applied Research Network (PECARN). The authors looked at test characteristics of the urinalysis based on infants with and without accompanying bacteremia based on two definitions of UTI—growth of greater than 50,000 or greater than 10,000 colony forming units (CFUs) per ml of urine. A UA was considered “positive” for a UTI if there was evidence of positive leukocyte esterase, nitrite, or pyuria in the assessment of an infant’s urine.
At both UTI definitions, the UA in this study proves to be quite accurate and sensitive for identifying a UTI. So should we simply redefine a UTI from its previous definition of greater than 50,000 to 10,000 CFUs per ml per the AAP Clinical Guidelines published in 2011 (10.1542/peds.2011-1330)? To better understand that question, we asked two authors of the AAP’s Clinical Practice UTI Guidelines Drs. Ken Roberts and Ellen Wald to add their input in an accompanying commentary to this study. They review the work leading to how we got to 50,000 CFUs per ml and raise possible concerns that values lower than that in the absence of fever might represent contamination or asymptomatic bacteriuria--hence the reaffirmation of the AAP guidelines in 2016. However when you add fever into the equation of pyuria and colony count, Drs. Roberts and Wald (10.1542/peds.2017-3239) believe that based on the new study by Tzimenatos et al. that 10,000 CFUs per ml is a reasonable threshold to diagnose a UTI in febrile infant. Do you agree? Go with the flow of this study and commentary and read both to learn more and decide if your threshold for UTI drops to 10,000 CFUs or not.