A Comparative Study of the Epidemiological Aspects of Legionnaires' Disease: Outbreaks in Korea and Japan, 2010 - 2014.

Background: In the present study, we compared the epidemiological aspects of Legionnaire' disease (LD) outbreaks in Korea and Japan by analyzing the current state from 2010 to 2014.

Methods: The following factors were analyzed: nationwide cumulative incidence rate (CIR) per 100,000 populations and case-fatality rate in percentage, epidemiological aspects (i.e., case related to gender), male to female morbidity ratio (MFMR), age, seasonality and habitat distribution of LD cases.

Results: In total, there were 134 cases of LD with the CIR of 0.05 per 100,000 populations in Korea from 2010 to 2014. During the same period in Japan, there were 4,840 cases of LD with a CIR of 0.76 per 100,000 populations. The CIR in Japan was significantly higher than that in Korea. However, the case-fatality rates were at similar levels (3.0% vs. 5.9%). Moreover, LD affects both sexes differently, accounting for 2.05 and 4.41 of MFMR in Korea and Japan, respectively. In both countries, the incidence mainly occurred among people aged 40 years or older, and peaked in summer (37.3% vs. 33.7% of total cases). Significant differences were observed in the incidence of LD cases between the capital city and county areas in both two countries. These differences in LD risk factors reflect the different influences of reservoir/host with natural or artificial aquatic environments.

Conclusion: This study provides a quantitative analysis of the epidemiological aspects and risk factors of LD outbreaks in Korea and Japan. We hope this study would be helpful for providing insight on effective future strategies to reduce LD outbreaks.