Basic Reproduction Number of Enterovirus 71 and Coxsackievirus A16 and A6: Evidence From Outbreaks of Hand, Foot, and Mouth Disease in China Between 2011 and 2018.

BACKGROUND: Enterovirus 71 (EV-A71), coxsackievirus A16 (CV-A16), and coxsackievirus A6 (CV-A6) are common serotypes causing hand, foot, and mouth disease (HFMD). Analyses on the basic reproduction number (R0) of common pathogens causing HFMD are limited and there are no related studies using field data from outbreaks in mainland China. METHODS: We estimated the pathogen-specific basic reproduction number based on laboratory-confirmed HFMD outbreaks (clusters of ≥10 HFMD cases) reported to the national surveillance system between 2011 and 2018. The reproduction numbers were calculated using a mathematical model and the cumulative cases during the initial growth periods. RESULTS: This study included 539 outbreaks, of which 198 were caused by EV-A71, 316 by CV-A16, and 25 by CV-A6. All 10 417 cases involved were children. Assuming the outbreaks occurred in closed systems and the incubation period is 5 days, the median (interquartile range [IQR]) R0 estimates of EV-A71, CV-A16, and CV-A6 were 5.06 (2.81, 10.20), 4.84 (3.00, 9.00), and 5.94 (3.27, 10.00). After adjusting for seroprevalences, the R0 (IQR) estimates for EV-A71, CV-A16 (optimistic and conservative scenarios), and CV-A6 were 12.60 (7.35, 25.40), 9.29 (6.01, 19.20), 15.50 (9.77, 30.40), and 25.80 (14.20, 43.50), respectively. We did not observe changes in the R0 of EV-A71 after vaccine licensure (P = .67). CONCLUSIONS: HFMD is highly transmissible when caused by the 3 most common serotypes. In mainland China, it primarily affects young children. Although a vaccine became available in 2016, we have not yet observed any related changes in the disease dynamics.