Catheter-obtained, Enterococcus and Proteus positive urine cultures may represent mostly contamination or asymptomatic bacteriuria in infants <90 days

Background: Urinary tract infection (UTI) diagnosis in infants is often made by a positive urine culture result, regardless of urine dipstick findings.

Aim: To assess parameters that may affect positive urine culture results interpretation in infants, including dipstick performance, obtainment method, bacteria type, age and laboratory results.

Methods: A retrospective, cohort study. Infants <90 days with urine dipstick and culture obtained through subrapubic aspiration (SPA) or catheter, 2015-2016, were included.

Results: Overall, 19% (129/678) of cultures were positive. The dipstick sensitivity was 51% for all cultures; 66%, 47%, 15% and 10% for Escherichia coli (n= 71), Klebsiella (n= 19), Enterococcus (n= 34) and Proteus (n= 10), respectively (p<.001). Sensitivity was higher in SPA vs. catheter for all cultures (67% vs. 43%); E. coli (78% vs. 59%); and Klebsiella (88% vs. 18%). For Enterococcus, dipstick sensitivity was low in both SPA and catheter (0-16%). All Proteus episodes were catheter obtained. Positive culture with negative dipstick and Enterococcus episodes had lower C-reactive protein levels, and higher proportion of mixed infection compared with positive dipstick and E. coli episodes.

Conclusions: Urine cultures in infants should be obtained by SPA, since catheter-obtained, Enterococcus and Proteus positive cultures may represent contamination or asymptomatic bacteriuria, rather than true UTI.