Estimation of the basic reproduction number of enterovirus 71 and coxsackievirus A16 in hand, foot, and mouth disease outbreaks.

Ma, Edmond; Fung, Connie; Yip, Steven H L; Wong, Christine; Chuang, Shuk Kwan; Tsang, Thomas

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 (R0) for these enteroviruses. METHODS We estimated the R0 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 Râ‚€ 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 Râ‚€ 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 Râ‚€ of EV71 was 5.48 with an interquartile range of 4.20 to 6.51, whereas the median Râ‚€ of Cox A16 was 2.50 with an interquartile range of 1.96 to 3.67. The Râ‚€ of EV71 was significantly higher than that of CoxA16, P = 0.002; and sensitivity analysis showed the same results. The Râ‚€ was not associated with outbreak settings, sizes of the institutions, or number of persons affected. CONCLUSIONS The Râ‚€ for EV71 and for Cox A16 was determined using a model which showed that the Râ‚€ 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.