Mathematical model for SARS transmission. Susceptible individuals are infected by infectious, undetected individuals and become infectious themselves after a stage of latency. Infectious individuals lose infectiousness by death, recovery, or isolation. No births or deaths from non-SARS causes are considered. When quarantine is implemented, a proportion, q, of new infections are quarantined before they become infectious; additionally, the same proportion of susceptible individuals who were contacts of infectious persons but were not infected are also quarantined. Susceptible individuals are released from quarantine after 10 days; for simplicity, we assume that quarantined individuals are isolated before they can infect anyone else and that compliance with quarantine is complete (SOM Text).