Meteorological Factors Facilitated Increased Legionnaires’ Disease Notifications and Mortality Pre-COVID-19 and COVID-19 in Hong Kong

Annual notification number of Legionnaires’ disease (LD) increased from 66 cases in 2015 to 104 cases in 2020 in Hong Kong, with a case fatality rate (CFR) of 17.3% in 2020. This study investigated possible meteorological factors associated with confirmed LD cases and deaths. The negative binomial regression model was used for monthly LD confirmed cases and the Poisson regression model was used for monthly LD mortality cases. A decision tree model was adopted to identify the thresholds of meteorological factors if any. The confirmed LD cases were highest in July while the LD mortality was highest in August. A negative binomial regression model confirmed that maximum air temperature (P=0.081, RR=1.3, 95% CI=0.97-1.75) and rainfall (P=0.009, RR=1.02, 95% CI=1.0004-1.003) were positively correlated with the increase in confirmed LD cases. A Poisson regression model confirmed that maximum air temperature (P=0.034, RR=1.71, 95% CI=1.04-2.80) was positively correlated with the surge in LD mortality. When rainfall exceeds 78.8 mm, the public should be alerted of the increased risk of contracting LD. Temperature and rainfall were positively associated with the confirmed LD cases in Hong Kong.