Environmental and social driving factors in shaping the transmissibility and seasonality of hand, foot, and mouth disease (HFMD) in South Korea and Hong Kong

Background: Hand, foot, and mouth disease (HFMD) is a common contagious viral illness that primarily affects young children. It typically occurs seasonally, with a peak during spring or summer in temperate regions. However, its transmission patterns are less regular in the tropics and subtropics with year-round circulation. In this study, we investigated the impacts of various drivers of HFMD transmission and seasonality across two distinct climatic locations: Hong Kong (a subtropical city) and South Korea (a temperate country). Methods: We collected weekly surveillance data for HFMD in Hong Kong and South Korea during 2010–2019 and inferred the instantaneous reproduction number (R_t) to measure the time-varing transmissibility of HFMD. Univariate regression models were employed to examine the associations between transmissibility and meteorological and social drivers. Additionnaly, multivariate regressions with lag analyses were conducted to quantify the impcats of different intrinsic and extrinsic drivers on transmissibility (R_t) and their seasonality. Findings: We identified the depletion of susceptible and inter-seasonal factors as key intrinsic drivers for HFMD transmissibility and seasonality, explaining 30 % and 70 % of variance in R_t in Hong Kong and South Korea, respectively. Temperature, absolute humidity and school closures were significant extrinsic drivers explaining up to an additional 10 % −13 % variance in R_t in both locations. A non-linear inverted U-shaped form of association for temperature and absolute humidity with HFMD transmissibility improved model predictions, explaining up to 7–8 % variability of the transmissibility individually in both locations. Interpretation: Seasonal transmission patterns of HFMD in two different locations in Hong Kong and South Korea were driven by depletion of susceptible individuals and inverted U-shaped associations with temperature and absolute humidity.