When HFMD crashes into birthday: A novel discovery of birthday week effect based on evidence from fifteen years (2008-2022)’s surveillance in China (Preprint)

BACKGROUND Hand, foot and mouth disease (HFMD) is a major infectious disease that primarily affects infants and children worldwide. Previous studies of HFMD mainly focused on natural regularity, such as seasonality, but exploration of important social time point’s influence was lack. Several studies have indicated correlations between birthday and some disease outcomes. OBJECTIVE For the first time ever, to explore birthday’s influence on hand, foot and mouth disease (HFMD) in Yunnan, China. METHODS 2008-2022 HFMD surveillance data in Yunnan Province, China were obtained. The six days before birthday to the exact birthday were defined as the birthday week. Birthday week effect was measured by the proportion of cases during the birthday week (birthday week proportion, BWP). In subgroup analyses, the BWPs across sex, different age groups, months of birth and reporting years were presented. RESULTS Among total 973 410 cases, 116 976(12.02%) occurred during the birthday week, which was 6.27 times relative to the average weekly proportion (7/365, 1.92%). Specifically, the BWPs reached up to 33.67% for 0-1 year infants, which was 17.57 times to the average weekly proportion. The BWPs were close between males and females (12.19% vs 11.78%). Patients born in April-July, the main peak months of HFMD epidemic, had higher BWPs (13.51%, 20.06%, 19.69% and 15.60%) than other months. Especially for 0-1 year infants born in April-July, the BWPs were as high as 43.54%, 51.85%, 48.10% and 39.42%, respectively. Besides, there was a decreasing trend of BWPs from 2008 to 2022 (33.74% to 2.77%). CONCLUSIONS An obvious birthday week effect of HFMD was observed, especially for infants and patients born at the peak months of epidemic. The improvements in surveillance quality might explain the decreasing trend of birthday week effect over year. While, higher exposure risk during birthday period and possible biological mechanisms might also accounted for this phenomenon. To some extent, raising people’s awareness of greater risk during birthday week will benefit HFMD’s prevention and control.