Transmission Dynamics of the Etiological Agent of SARS in Hong Kong: Impact of Public Health Interventions.

Riley S, Fraser C, Donnelly CA, Ghani AC, Abu-Raddad LJ, Hedley AJ, Leung GM, Ho LM, Lam TH, Thach TQ, Chau P, Chan KP, Lo SV, Leung PY, Tsang T, Ho W, Lee KH, Lau EM, Ferguson NM, Anderson RM.

　　Department of Infectious Disease Epidemiology, Faculty of Medicine, Imperial College London, Exhibition Road, London SW7 2AZ, UK.
　　We present an analysis of the first 10 weeks of the severe acute respiratory syndrome (SARS) epidemic in Hong Kong. The epidemic to date has been characterized by two large clusters, initiated by two separate "super-spread" events (SSEs), and ongoing community transmission. By fitting a stochastic model to data on 1512 cases, including these clusters, we show that the etiological agent of SARS is moderately transmissible. Excluding SSEs, we estimate 2.7 secondary infections were generated per case on average at the start of the epidemic, with a substantial contribution from hospital transmission. Transmission rates fell during the epidemic, primarily due to reductions in population contact rates and improved hospital infection control, but also as a result of more rapid hospital attendance by symptomatic individuals. As a result, the epidemic is now in decline, though continued vigilance is necessary for this to be maintained. Restrictions on longer-range population movement are shown to be a potentially useful additional control measure in some contexts. We estimate that most currently infected persons are now hospitalized, emphasizing the importance of control of nosocomial transmission.