Estimation of the Basic Reproduction Number of Enterovirus 71 and Coxsackievirus A16 in Hand, Foot, and Mouth Disease Outbreaks

Background: Coxsackievirus A16 (Cox A16) and enterovirus 71 (EV71) are common pathogens causing hand, foot, and mouth disease (HFMD) in pediatric population. Little is known about the basic reproductive number (R-0) for these enteroviruses. Methods: We estimated the R-0 of EV71 and of Cox A16 from laboratory-confirmed HFMD outbreaks reported to the Department of Health, from 2004 to 2009. We derived a mathematical model and calculated R-0 based on the cumulative number of cases at the initial growth phase of the outbreaks, as determined by the epidemic curves. We tested the association of R-0 with settings and sizes of the institution and total number of persons affected. Results: We analyzed 34 outbreaks, 27 caused by Cox A16 and 7 caused by EV71. Assuming the incubation period to be 5 days, the median R-0 of EV71 was 5.48 with an interquartile range of 4.20 to 6.51, whereas the median R-0 of Cox A16 was 2.50 with an interquartile range of 1.96 to 3.67. The R-0 of EV71 was significantly higher than that of CoxA16, P = 0.002; and sensitivity analysis showed the same results. The R-0 was not associated with outbreak settings, sizes of the institutions, or number of persons affected. Conclusions: The R-0 for EV71 and for Cox A16 was determined using a model which showed that the R-0 for EV71 was higher than that of Cox A16. This finding helps better understand the transmission dynamics of HFMD outbreaks and formulate public health measures for controlling the disease.