Seasonality of hand-foot-and-mouth disease in Hong Kong and South Korea and impact of the COVID-19 pandemic

Abstract

<p><strong>Background & aims of study</strong></p><p>Similar to influenza, the hand-foot-and-mouth disease (HFMD) virus epidemics occur annually (with summer-peaks) in temperate locations, whereas epidemics can have weak seasonality in tropical and subtropical locations. The underlying mechanisms of HFMD seasonality remain difficult to disentangle, though several intrinsic and extrinsic drivers were proposed to have potential to modulate HFMD seasonality. We aimed to identify these drivers and quantify their role in transmissibility to predict HFMD seasonality in two distinct locations in Hong Kong and South Korea.</p><p><br></p><p><strong>Methods and Results</strong></p><p>We analyzed surveillance data on HFMD virus activity in Hong Kong and South Korea during 2014-2021. We first evaluated the transmissibility of HFMD by estimating instantaneous reproduction number (R_t) and then we used a series of nonlinear regression models to assess the underlying associations between these measures of transmissibility and different driving factors. Finally, we predicted the year-round influenza transmissibility driven by these factors, which might able to mimic the various seasonal pattern in HFMD transmission in these locations. We found that mean ambient temperature, absolute humidity and school holidays were the potential drivers of HFMD seasonality across the locations. The model with ambient temperature, absolute humidity and school holidays along with depletion of susceptible were able to explain up to 77% of total variance in R_t with a variation across the locations. However, most of the variation could be explained by depletion of susceptible and inter-seasonal factors where external drivers could explain 4% to 10% of variability in R_t. The joint prediction by temperature, absolute humidity and school closure could explain the HFMD seasonality of single peak and multiple peaks in these locations. We estimated significant reduction in HFMD transmissibility during COVID-19 pandemic across the locations.</p><p><br></p><p><strong>Implications</strong></p><p>The non-linear effect of temperature and humidity and negative association of school holidays on HFMD transmission may contribute to the distinct patterns of HFMD seasonality and allow improved predictions of both strong and weak seasonal circulation of HFMD virus across the latitudes.</p>