Descriptive epidemiology of acute pyelonephritis in Korea, 2010-2014: Population-based study

Background: Acute pyelonephritis (APN) is one of the most common community-acquired bacterial infections. Recent increases of antimicrobial resistance in urinary pathogens might have changed the other epidemiologic characteristics of APN. The objective of this study was to describe the current epidemiology of APN in Korea, using the entire population. Methods: From the claims database of the Health Insurance Review and Assessment Service in Korea, the patients with International Classification of Diseases, 10th Revision codes N10 (acute tubulo-interstitial nephritis) or N12 (tubulo-interstitial nephritis, neither acute nor chronic) as the primary discharge diagnosis during 2010-2014 were analyzed, with two or more claims during a 14-day period considered as a single episode. Results: The annual incidence rate of APN per 10,000 persons was 39.1 and was on the increase year to year (35.6 in 2010; 36.7 in 2011; 38.9 in 2012; 40.1 in 2013; 43.8 in 2014, P = 0.004). The increasing trend was observed in both inpatients (P = 0.014) and outpatients (P = 0.004); in both men (P = 0.042) and women (P = 0.003); and those aged under 55 years (P = 0.014) and 55 years or higher (P = 0.003). Eleven times more women were diagnosed and treated with APN than men (men vs. women, 6.5 vs. 71.3), and one of every 4.1 patients was hospitalized (inpatients vs. outpatients, 9.6 vs. 29.4). The recurrence rate was 15.8%, and the median duration from a sporadic episode (i.e., no episode in the preceding 12 months) to the first recurrence was 44 days. The recurrence probability increased with the number of previous recurrences. The average medical cost per inpatient episode was USD 1,144, which was 12.9 times higher than that per outpatient episode (USD 89). Conclusion: The epidemiology of APN in Korea has been changing with an increasing incidence rate.