Printed in U.S.A. DOI: 10.1093/aje/kwh308 The Epidemiology of Acute Pyelonephritis in South Korea, 1997–1999

Acute pyelonephritis causes significant morbidity, tends to recur, and can be fatal; however, little is known regarding its epidemiology. In this paper, the authors describe the epidemiology of acute pyelonephritis in South Korea by using nationwide heath insurance claims data from 1997 to 1999. The National Health Insurance System of South Korea covers almost the entire population (99%). The overall average annual incidence rate of pyelonephritis in 1997–1999 was 35.7 per 10,000 population (male, 12.6; female, 59.0). Approximately one of every seven patients was hospitalized (incidence per 10,000: inpatients, 5.5; outpatients, 30.1). Incidence varied with age and was higher in the summer season. Following an initial episode, the risk of a second episode within 12 months was 9.2 % for females and 5.7 % for males; by contrast, the risk of a fifth episode within a year following a fourth episode was 50.0 % for females and 53.0 % for males. Female sex (hazard ratio = 1.89, 95 % confidence interval: 1.60, 2.23), advancing age, outpatient treatments (hazard ratio = 1.35, 95 % confidence interval: 1.14, 1.60), and medical aid (hazard ratio = 1.23, 95 % confidence interval: 1.08, 1.40) increased the risk of any recurrence. Pyelonephritis has a clear seasonal pattern and high rate of recurrence. The incidence of hospitalization for pyelonephritis in South Korea is similar to that in the United States and Canada. hospitalization; nephritis, interstitial; pyelonephritis; recurrence; seasons Abbreviation: ICD-10, International Classification of Diseases, Tenth Revision