Objective To investigate the transmission dynamics parameters of coxsackievirus A16 (CVA16)-caused hand, foot, and mouth disease (HFMD) in primary schools in Shenzhen, Guangdong and elucidate its transmission characteristics and trends.

Methods A field epidemiological cross-sectional survey was conducted following the outbreak of CVA16-caused HFMD in a primary school in Shenzhen on September 14, 2024. Detailed investigations were performed on confirmed cases and close contacts. Additionally, symptom monitoring accompanied by nucleic acid testing was carried out over a two-week period. Sampling was discontinued upon obtaining two consecutive negative nucleic acid test results. The incubation period distribution was modeled via three parametric approaches: log-normal distribution, gamma distribution, and weibull distribution. The basic reproduction number (R0) was estimated from the cumulative number of reported cases during the initial growth phase of the outbreak. The serial interval was estimated by a Bayesian approach, and the posterior distribution of the model parameters was estimated by the Markov Chain Monte Carlo (MCMC) method.

Results  Among 96 susceptible individuals under investigation during the outbreak of CVA16-caused HFMD at a primary school in Shenzhen, 43 cases, encompassing both confirmed cases and close contacts, were identified. Fourteen cases were laboratory-confirmed as CVA16 positive in HFMD, indicating an attack rate of 14.58% (14/96). Goodness-of-fit analysis of the three parametric distribution models revealed that the weibull distribution provided the optimal characterization of the incubation period for CVA16-caused HFMD in primary schools in Shenzhen. The weibull distribution showed the Watanabe-Akaike Information Criterion (WAIC) and Leave-One-Out Cross-Validation Information Criterion (LOOIC) values of 52.7 and 52.8, respectively, outperforming both the gamma distribution (WAIC = 53.3, LOOIC = 53.4) and log-normal distribution (WAIC = 53.3, LOOIC = 53.3). The weibull distribution revealed a mean incubation period of 3.0 days (95%CrI: 2.2 d–4.0 d) for CVA16-caused HFMD, estimating an incubation period shorter than 0.5 day in 2.5% of the cases and an incubation period shorter than 6.3 days in 97.5% of the cases. The outbreak persisted for 9 days, and the estimated R0 was 1.94. It meant a single infected individual can transmit the infection to approximately 2 secondary cases on average, without any intervention measures. Six infection sources and eleven transmission chains with variable estimated serial intervals and credible intervals were identified. The combined average serial interval was calculated to be 4.2 days (95%CrI: 1.9 d–6.4 d).

Conclusions CVA16-casued HFMD in the primary schools in Shenzhen is characterized by a short incubation period, a high R0, and complex transmission chains, necessitating a comprehensive prevention and control strategy.