Figure 3.

Estimated effective reproduction number (R_t) (number of secondary infections generated per primary case) during the SARS epidemic in China. Values represent average R_t (central white line) and associated 95% (grey) and 80% (black) confidence intervals, by date of symptom onset. The critical value of R_t=1, below which sustained transmission is impossible, is marked with a broken horizontal line. Arrows reflect the moment of important events and public health control measures: (1) Local newspaper report about outbreak of unknown infectious disease in Guangdong (2 January); (2) Start of control in Guangdong hospitals: e.g. isolation, contact tracing (1–3 February); (3) First official report of outbreak by Guangdong authorities (11 February); (4) WHO global alerts; first mentioning of SARS (12–15 March); (5) First protocol of SARS control; start isolation in Beijing hospitals (2 April); (6) Full control under central guidance by the Chinese authorities, including mandatory reporting of SARS; definition of diagnostic criteria and treatment (11–14 April); (7) Stringent control measures: quarantine in airports and stations; closure of schools, universities and public places; daily reporting by the national media (19–26 April); (8) Public holiday cancelled; new 1000-bed SARS hospital opened (1 May); (9) Further improvement of various guidelines and protocols (4–9 May).