Urinary tract infections in young infants with a normal urine dipstick.

Aim: To assess missed urinary tract infections (UTI) in febrile infants ≤2 months when adhering to recent guidelines suggesting not to send a urine culture with a negative dipstick.

Methods: A retrospective cohort study of 308 infants ≤2 months with a positive urine culture admitted in 2013-2023, divided into subgroups without exposure to urine dipstick results: 'urosepsis' (UTI with bacteraemia), 'UTI' (positive urine culture, elevated inflammatory markers, no other cause of fever) and 'bacteriuria' (positive urine culture, not meeting the above-mentioned criteria). After retrieving the dipstick results, the 'missed UTI' group (UTI+ negative dipstick) was described.

Results: A negative dipstick was found in 2/20 (10%), 32/127 (25%) and 126/161 (78%) of infants with 'urosepsis', 'UTI' and 'bacteriuria', respectively. In the 'missed UTI' group (n = 34), there were more non-Escherichia coli UTI (68% vs. 9% with positive dipstick, p < 0.001), and lower inflammatory markers (leukocytes 15.5 vs. 17.2 k/μL, p = 0.007, C-reactive protein 21 vs. 58 mg/L, p < 0.001). Three infants had high-grade vesicoureteral reflux (VUR) and renal scarring.

Conclusions: There is a non-negligible rate of infants ≤2 months with UTI and without pyuria, including those with urosepsis, VUR and renal scarring. We suggest obtaining a urine culture regardless of dipstick results.