Transmission dynamics of hand, foot and mouth disease in China

Abstract

Hand, foot and mouth disease (HFMD) causes substantial burden among children in Asia. Monovalent vaccines against HFMD have been licensed in mainland China since 2015. The transmission dynamics of the disease may be affected by the application of the vaccines. However, uncertainty surrounding the transmission dynamics of pathogens which can cause HFMD would impair the optimization of prevention and control strategies. I conducted an epidemiological study using national surveillance data from 2008 to 2015. I first conducted a wavelet analysis on HFMD epidemics, and found all the serotypes circulated annually in China. I estimated the serotype-specific severity risks of HMFD, and found the case-fatality risks decreased with age, while EV-A71 infections were associated with the highest case-fatality risks among each age group. I conducted a spatial-temporal analysis on HFMD transmission dynamics using the national surveillance data in China, and found the synchrony of HFMD epidemics was associated with latitude, climate and population size but not longitude, while spatial transmission had limited an impact on HFMD epidemics. I then estimated the time-dependent transmissibility of HFMD, and found the local transmission of HFMD would be affected by absolute humidity and the Chinese New Year (CNY) period, while summer school holidays and spatial transmission appear to have limited effects on the local transmission of HFMD. I applied similar methods to data on HFMD related hospitalizations in Hong Kong, and found both absolute humidity and summer holiday appeared to have limited effects on the local HFMD transmission. I estimated the prevalence and severity profile of the EV-A71 infection based on published data. I found that maternal immunity against EV-A71 waned at 5 months of age, and the seroprevalence of EV-A71 antibody increased with age. I found 11.4% of children at age of 6 to 35 months were infected by EV-A71 in 2013, while only 7.2% of infected children would be eventually diagnosed as an HFMD case. In conclusion, all laboratory-confirmed EVs serotype categories circulated annually in China during 2008 and 2015. I found highly synchronized HFMD epidemics across provinces, which were mostly driven by climate. Local transmission appeared to be the major route for HFMD transmission, which could be increased by higher absolute humidity and the CNY break. I found EV-A71 remained to be the most virulent causative serotype of HFMD, and 0.3% of EV-A71 infections could develop severe complications. Infants younger than 1 year of age were at the highest fatality risk after EV-A71 infection, and maternal immunity against EV-A71 usually waned at five months of age.