Risk Factors Associated with Acute Pyelonephritis in Healthy Women

BACKGROUND: Although most cases of acute pyelonephritis occur in otherwise healthy women, data on risk factors for this condition are lacking. OBJECTIVE: To evaluate infection characteristics, incidence, and risk factors associated with acute pyelonephritis in a sample of women. DESIGN: Population-based case-control study. SETTING: Group Health Cooperative, a prepaid health plan in Washington. PARTICIPANTS: 788 nonpregnant women, 18 to 49 years of age. Case-patients (n = 242) were women with pyelonephritis who were identified from computerized databases. Controls were 546 similar-age women with no pyelonephritis diagnosis in the previous 5 years who were randomly selected from enrollment databases. Response rates for case-patients and controls were 73% and 64%, respectively. MEASUREMENTS: Characteristics of infection and potential risk factors for pyelonephritis, ascertained through computer-assisted telephone interview and computerized databases. RESULTS: 7% of case-patients were hospitalized. Escherichia coli was the infecting pathogen in 85% of cases. In multivariable models, factors associated with pyelonephritis risk were frequency of sexual intercourse in the previous 30 days (odds ratio, 5.6 95% CI, 2.8 to 11.0 for > or =3 times per week), recent urinary tract infection (UTI) (odds ratio, 4.4 CI, 2.8 to 7.1), diabetes (odds ratio, 4.1 CI, 1.6 to 10.9), recent incontinence (odds ratio, 3.9 CI. 2.6 to 5.9), new sexual partner in the previous year (odds ratio, 2.2 CI, 1.4 to 3.6), recent spermicide use (odds ratio, 1.7 CI, 1.1 to 2.8), and UTI history in the participant's mother (odds ratio, 1.6 CI, 1.1 to 2.5). Risk factors for selected subgroups (patients 30 years of age, patients with no UTI history, and inpatients) were also evaluated. LIMITATIONS: Potential recall bias, reliance on automated case definition criteria, and limited data on diabetes and incontinence variables. CONCLUSIONS: Few nonpregnant, community-dwelling women younger than 50 years of age with pyelonephritis are hospitalized. As with cystitis in reproductive-age women, sexual behaviors and patient and family history of UTI are associated with increased pyelonephritis risk. Diabetes and incontinence also seem to independently increase the risk for pyelonephritis.