O2182: Time-varying Exposure Analysis of Infants with Isolated Hydronephrosis: An Epidemiological Study

Background: Some studies have reported that hydronephrosis may predispose children to urinary tract infections (UTIs). Isolated hydronephrosis is defined as dilatation of the renal pelvis without other abnormalities. There is yet to be consensus on the use of continuous antibiotic prophylaxis (CAP) for patients with isolated hydronephrosis. Herein, we evaluate the risk of UTI using individualized patient data and time-varying exposure analysis.

Methods: Our institutional hydronephrosis database was examined. Urinary tract infection was defined as fever >38.5, with positive urinalysis and culture from catheterized specimens. Only the UTIs within the first year of life were included. To adjust for time-varying exposure, patients were censored based on the maximum follow-up of 365 days and CAP discontinuation, UTI event, surgery (pyeloplasty), loss to follow-up, or hydronephrosis resolution. Survival analysis and incidence per 1000 person days were calculated.

Results: A total of 578 patients were seen prior to their first UTI episode and segregated into two groups based on exposure to prophylaxis. Of these, 271 (46.8%) did not have exposure to CAP. There were similar numbers of bilateral hydronephrosis in each group (58/284, 20.0% vs. 73/325, 21.5%). There was a higher proportion of SFU grade ≥3 in the CAP group (88/284, 30.9% vs. 137/325, 42.5%). There were 2 UTI events in the no CAP group (incidence 0.025 per 1000-person-days) and 3 in the CAP exposure group (incidence 0.050 per 1000-person days). Kaplan-Meier survival curve, accounting for time-varying exposure censoring, showed no difference in time to UTI between the two groups (Figure 1, p=0.511).

Conclusion: The rates of UTIs in patients with isolated hydronephrosis are very low. Risk adjusted analysis of individualized patient data suggests that CAP does not seem to significantly reduce the likelihood of UTIs in patients with isolated hydronephrosis. This information is valuable for both pre- and postnatal recommendations and management.