We appreciate the thoughtful comments by Dr Tsujimoto and colleagues, who are concerned that our sensitivity estimates may mislead practitioners to assume that a negative urinalysis (UA) rules out bacteremic UTI (or UTI in general). The intent of our study was not to assess whether a UA rules in or rules out bacteremic UTI, but rather to analyze the UA in a population of infants with definitive infection. Although Tsujimoto et al are concerned that the UA sensitivity is overestimated in our study, we are similarly concerned that all previous studies have underestimated the UA sensitivity by using the urine culture as a gold standard when in fact many “positive” urine cultures reflect contamination or asymptomatic bacteruria. Whether bacteremic UTI represents UTI in general or represents a more severe form of UTI is debatable. Most investigations comparing infants with bacteremic versus nonbacteremic UTI have demonstrated few if any clinical differences on presentation, and even these few differences may be explained by inclusion of infants with asymptomatic bacteruria or contamination in the nonbacteremic UTI groups. However, few would disagree that bacteremic UTI (isolation of the same pathogenic organism from the blood and urine) represents true infection. Because of the entities of asymptomatic bacteruria and contamination, the lack of a reliable gold standard for the diagnosis of UTI will be a perpetual problem,1 and we believe that bacteremic UTI offers a unique way to assess the performance of the UA in an infant who has a true infection.
Tsujimoto et al are also concerned that a positive UA might trigger practitioners to obtain a blood culture, and suggest that this might create “review bias.” We agree that this bias, which is also called “verification bias” or “confirmation bias,” tends to falsely elevate sensitivity and falsely lower specificity, because subjects with negative index tests are underrepresented.2 However, we are confident that this potential bias is not a limitation of our study. Infants <1 month of age routinely undergo a full workup for serious bacterial infection independent of the preliminary results, and the sensitivity estimates were the same in this age group as they were in the 1- to 3-month age group.
How our study findings will affect practitioners’ interpretation of the combined findings of a negative UA and a positive urine culture, or their willingness to rely on the UA as a screening test, may depend in part on how practitioners weigh the risks of undertreatment versus overtreatment of UTI. Traditional practice patterns have erred toward avoidance of undertreatment by interpreting all positive urine cultures in young infants as true UTI irrespective of the UA, and in so doing have led to long courses of antibiotics, hospitalizations, and invasive urinary imaging that may have been unnecessary. We believe that our new findings should force us to rethink this practice, and that, as stated in the accompanying commentary by Ken Roberts, the absence of inflammation (pyuria and/or leukocyte esterase) on the UA “should create great doubt about the presence of a UTI.”1
Conflict of Interest:
- Copyright © 2015 by the American Academy of Pediatrics