Risk of Pyelonephritis by Index Antibiotic Agent, IBM® MarketScan® Commercial Database, 2006–2015. Cumulative risks and risk differences were estimated using standardized mortality ratio- weighted Kaplan-Meier functions. 95% confidence intervals were computed using a non-parametric bootstrap. Risk difference estimates greater than zero indicate higher risk of pyelonephritis compared to nitrofurantoin (reference). Estimates were adjusted for age, month, year, geographic region, provider type, drug or alcohol abuse, deficiency anemias, chronic pulmonary disease, depression, psychoses, hypertension, obesity, initial receipt of urinalysis, and initial receipt of urine culture.