The Epidemiology of Severe Acute Respiratory Syndrome in the 2003 Hong Kong Epidemic: An Analysis of All 1755 Patients

2 November 2004 | Volume 141 Issue 9 | Pages 662-673

Background: As yet, no one has written a comprehensive epidemiologic account of a severe acute respiratory syndrome (SARS) outbreak from an affected country.

Objective: To provide a comprehensive epidemiologic account of a SARS outbreak from an affected territory.

Design: Epidemiologic analysis.

Setting: The 2003 Hong Kong SARS outbreak.

Participants: All 1755 cases and 302 deaths.

Measurements: Sociodemographic characteristics; infection clusters by time, occupation, setting, and workplace; and geospatial relationships were determined. The mean and variance in the time from infection to onset (incubation period) were estimated in a small group of patients with known exposure. The mean and variance in time from onset to admission, from admission to discharge, or from admission to death were calculated. Logistic regression was used to identify important predictors of case fatality.

Results: 49.3% of patients were infected in clinics, hospitals, or elderly or nursing homes, and the Amoy Gardens cluster accounted for 18.8% of cases. The ratio of women to men among infected individuals was 5:4. Health care workers accounted for 23.1% of all reported cases. The estimated mean incubation period was 4.6 days (95% CI, 3.8 to 5.8 days). Mean time from symptom onset to hospitalization varied between 2 and 8 days, decreasing over the course of the epidemic. Mean time from onset to death was 23.7 days (CI, 22.0 to 25.3 days), and mean time from onset to discharge was 26.5 days (CI, 25.8 to 27.2 days). Increasing age, male sex, atypical presenting symptoms, presence of comorbid conditions, and high lactate dehydrogenase level on admission were associated with a greater risk for death.

Limitations: Estimates of the incubation period relied on statistical assumptions because few patients had known exposure times. Temporal changes in case management as the epidemic progressed, unavailable treatment information, and several potentially important factors that could not be thoroughly analyzed because of the limited sample size complicate interpretation of factors related to case fatality.

Conclusions: This analysis of the complete data on the 2003 SARS epidemic in Hong Kong has revealed key epidemiologic features of the epidemic as it evolved.

Editors' Notes Context Few comprehensive studies describe the 2003 outbreak of severe acute respiratory syndrome (SARS). Contribution This epidemiologic analysis of 1755 cases from Hong Kong found that most cases clustered in hospitals and residential buildings. Close human contact and spread by a sewage system probably explain the clustering. The outbreak lasted about 3 months. The estimated mean incubation period was 4.6 days, and the case-fatality ratio was 17%. Factors associated with increased risk for death included older age and male sex. Implications The observed patterns suggested that SARS had low transmissibility, except in settings of intimate contact or clinically significant environmental contamination. –The Editors

 

Author and Article Information

From University of Hong Kong, Government of the Hong Kong Special Administrative Region, and Hong Kong Hospital Authority, Hong Kong, China, amd Imperial College, University of London, London, United Kingdom.

Acknowledgments: The authors thank P.C. Lai for the geographic information system analysis, all their colleagues in the Hong Kong Department of Health and Hong Kong Hospital Authority who were involved with the public health control of the SARS epidemic and data collection and processing, the Hong Kong Hospital Authority SARS Collaborative Group for supplying some of the data fields in the regression model, and Marie Chi for her expert secretarial assistance in the preparation of the manuscript.

Grant Support: By the University of Hong Kong SARS Research Fund, a special commissioned project grant from the Research Fund for the Control of Infectious Disease, Government of the Hong Kong Special Administrative Region, and a European Union specific targeted research or innovation project contract (SARSTRANS). Drs. Ghani and Ferguson acknowledge fellowship support from The Royal Society, and Drs. Fraser and Ferguson acknowledge research funding from the Medical Research Council. Drs. Riley and Ferguson thank the Howard Hughes Medical Institute, and Dr. Anderson thanks the Wellcome Trust and the European Union.

Potential Financial Conflicts of Interest: None disclosed.

Requests for Single Reprints: Tai-Hing Lam, MD, FFPH, Department of Community Medicine, 21 Sassoon Road, Faculty of Medicine Building, University of Hong Kong, Pokfulam, Hong Kong, China; e-mail, commed{at}hkucc.hku.hk.

Current Author Addresses: Drs. G.M. Leung, Hedley, Ho, Thach, and Lam, Ms. Chau, and Ms. I.O.L. Wong: Department of Community Medicine and School of Public Health, University of Hong Kong, 21 Sassoon Road, Pokfulam, Hong Kong, China.

Drs. Ghani, Fraser, Anderson, Donnelly, Riley, and Ferguson: Department of Infectious Disease Epidemiology, Imperial College London, St Mary's Campus, Norfolk Place, London W2 1PG, United Kingdom.

Drs. Tsang and P.-Y. Leung: Department of Health, Government of the Hong Kong Special Administrative Region, Wu Chung House, Wanchai, Hong Kong, China.

Drs. V. Wong and Chan and Ms. Tsui: Hong Kong Hospital Authority, 147 Argyle Street, Kowloon, Hong Kong, China.

Dr. Lo: Health, Welfare and Food Bureau, Government of the Hong Kong Special Administrative Region, Murray Building, Central, Hong Kong, China.

Author Contributions: Conception and design: G.M. Leung, A.J. Hedley, T.-H. Lam.

Analysis and interpretation of the data: G.M. Leung, A.J. Hedley, L.-M. Ho, T.Q. Thach, A.C. Ghani, C.A. Donnelly, C. Fraser, S. Riley, N.M. Ferguson, R.M. Anderson, T.-H. Lam.

Drafting of the article: G.M. Leung.

Critical revision of the article for important intellectual content: A.C. Ghani, C.A. Donnelly, C. Fraser, S. Riley, N.M. Ferguson, R.M. Anderson, V. Wong, J.C.K. Chan, E. Tsui, S.-V. Lo.

Final approval of the article: G.M. Leung, A.J. Hedley, L.-M. Ho, I.O.L. Wong, A.C. Ghani, C.A. Donnelly, C. Fraser, S. Riley, N.M. Ferguson, R.M. Anderson, S.-V. Lo, T.-H. Lam.

Provision of study materials or patients: T. Tsang, P.-Y. Leung, V. Wong, J.C.K. Chan, E. Tsui.

Statistical expertise: L.-M. Ho, P. Chau, I.O.L. Wong, T.Q. Thach.

Obtaining of funding: G.M. Leung, A.J. Hedley, T.-H. Lam.

Administrative, technical, or logistic support: P. Chau, T. Tsang, P.-Y. Leung, V. Wong, J.C.K. Chan, S.-V. Lo.

Collection and assembly of data: P. Chau, I.O.L. Wong, T.Q. Thach, T. Tsang, P.-Y. Leung, E. Tsui.