Epidemiological Characteristics of Imported Influenza A (H1N1) Cases during the 2009 Pandemic in Korea

OBJECTIVES: Quarantine measure for prevention of epidemic disease and further evaluations of their efficiency are possible only by elaborating analyses of imported cases. The purpose of this study was to analyze descriptive epidemiological characteristics of pandemic influenza A (H1N1) cases imported to Korea. METHODS: We collected two sets of data. The first set, comprised daily reported cases of H1N1 obtained from local cities in accordance with government policy about mandatory reporting of all H1N1 cases during May 1 to August 19, 2009. The second set, including 372 confirmed imported H1N1 cases, identified from 13 National Quarantine Stations in the Korea Centers for Disease Control and Prevention from May 24 to December 31, 2009. However, given the lack of information on the nature of the imported H1N1 cases from the two data sets during the over lapping period from May 24 to August 19, we express the number of imported cases as a range for this period. RESULTS: We estimated that the number of imported H1N1 cases from May 1 to August 19, 2009, was between 1,098 and 1,291 and the total number of cases was 2,409 to 2,580. We found the number of imported cases was beginning to diminish as of August. A analysis of the second data set showed that the distribution of sex was similar (males 50.7%, females 49.3%) and the age distribution from 20 to 59 was 61.5% and that of 60 and over was 0.8% of the 372 cases. We identified 25 countries where people infected with H1N1 traveled and 67.5% were in Asia. But the proportion of cases (/1,000) by region shows Oceania (0.199), South America (0.118), Southeast Asia (0.071), North America (0.049), Europe (0.035), and Northeast Asia (0.016) in that order. The order of H1N1 peaking was the Southern Hemisphere, Tropics, and the Nothern Hemisphere. CONCLUSIONS: This study provided information that could make possible the evaluation of the government quarantine measure for stopping imported disease from causing community-acquired spread in the future.