A comparative epidemiologic analysis of SARS in Hong Kong, Beijing and Taiwan

Abstract

Background: The 2002-2003 Severe Acute Respiratory Syndrome (SARS) outbreak infected 8,422 individuals leading to 916 deaths around the world. However, there have been few epidemiological studies of SARS comparing epidemiologic features across regions. The aim of this study is to identify similarities and differences in SARS epidemiology in three populations with similar host and viral genotype.

Methods: We present a comparative epidemiologic analysis of SARS, based on an integrated dataset with 3,336 SARS patients from Hong Kong, Beijing and Taiwan, epidemiological and clinical characteristics such as incubation, onset-to-admission, onset-to-discharge and onset-to-death periods, case fatality ratios (CFRs) and presenting symptoms are described and compared between regions. We further explored the influence of demographic and clinical variables on the apparently large differences in CFRs between the three regions.

Results: All three regions showed similar incubation periods and progressive shortening of the onset-to-admission interval through the epidemic. Adjusted for sex, health care worker status and nosocomial setting, older age was associated with a higher fatality, with adjusted odds ratio (AOR): 2.10 (95% confidence interval: 1.45, 3.04) for those aged 51-60; AOR: 4.57 (95% confidence interval: 3.32, 7.30) for those aged above 60 compared to those aged 41-50 years. Presence of pre-existing comorbid conditions was also associated with greater mortality (AOR: 1.74; 95% confidence interval: 1.36, 2.21).

Conclusion: The large discrepancy in crude fatality ratios across the three regions can only be partly explained by epidemiological and clinical heterogeneities. Our findings underline the importance of a common data collection platform, especially in an emerging epidemic, in order to identify and explain consistencies and differences in the eventual clinical and public health outcomes of infectious disease outbreaks, which is becoming increasingly important in our highly interconnected world.

Figure 1

Estimated incubation distribution. (A) Hong Kong (n = 168), (B) Beijing* (n = 97) and (C) Taiwan (n = 156) using a non-parametric method (solid line) and fitted to a lognormal distribution (dashed line). (D) Comparison of estimated incubation distributions fitted to a lognormal distribution in Hong Kong (solid line), Beijing (dashed line), and Taiwan (dotted line). *The large steps seen in the non-parametric estimate in Beijing are aretefacts due to the small sample size.

Figure 2

Epidemiological characteristics in Hong Kong, Beijing and Taiwan. (A) Epidemic curve for Hong Kong, Beijing (based on our data and those from a Beijing dataset [15]), and Taiwan. B-D*: Time from onset to admission distribution for each 2-week period and onset-to-admission distribution for (B) Hong Kong, (C) Beijing and (D) Taiwan. * Patients admitted before symptom onset and periods with fewer than 10 cases were excluded.

Figure 3

Proportion of cases showing different symptoms on presentation in Hong Kong, Beijing (Hospital 302 only^†) and Taiwan. * Labels on the vertical axis have been jittered for better presentation. ^† Detailed symptom data were missing for Hospital 309 patients. ^‡ Malaise and rigor were not documented in Taiwan.