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

Gabriel M. Leung, MD, MPH; Anthony J. Hedley, MD, FRCP; Lai-Ming Ho, PhD; Patsy Chau, MStat; Irene O.L. Wong, MPhil, MMedSc; Thuan Q. Thach, PhD; Azra C. Ghani, PhD; Christl A. Donnelly, ScD; Christophe Fraser, PhD; Steven Riley, DPhil; Neil M. Ferguson, DPhil; Roy M. Anderson, PhD; Thomas Tsang, MBBS, FHKAM; Pak-Yin Leung, MBBS, FFPH; Vivian Wong, MBBS, FHKAM; Jane C.K. Chan, MD, FHKAM; Eva Tsui, MStat; Su-Vui Lo, MBChB, FFPH; and Tai-Hing Lam, MD, FFPH
[+] Article and Author 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@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.


Ann Intern Med. 2004;141(9):662-673. doi:10.7326/0003-4819-141-9-200411020-00006
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Our findings summarize the time course and patient location of Hong Kong's 2003 SARS outbreak and the characteristics of those infected. The time course of the epidemic was marked by an initial period of exponential growth that eventually started to decrease after 6 weeks of intensive public health control measures (22). Substantial geospatial clustering was observed, with several large clusters of SARS cases in hospital and residential settings and a high proportion of health care workers. These observations are largely consistent with those reported for the Singapore and Toronto outbreaks, where the hospital environment substantially amplified the risk for infection (14, 2324). The pattern of infection clusters (Table 1) also suggests that the transmissibility of viral infection is low, except in settings of intimate contact or where clinically significant environmental contamination has occurred. It may also suggest low infectiousness in patients for some days after the onset of clinical symptoms. In addition, the risk for acquiring infection varied significantly by age, with relatively few cases of infection and no deaths in children and adolescents. The reasons for this are unclear. One hypothesis relating to mild or asymptomatic infection in young patients has not been borne out by detailed serologic testing of case contacts (25). Alternative hypotheses, including one that suggests that more recent infections in young patients with other coronaviruses confer some degree of protection to SARS coronavirus due to antigenic cross-reactivity, have not as yet been tested. Current prevailing theories focus on an attenuated immunopathologic response in children because of a more immature immune system (26). However, the exact mechanism that leads to SARS coronavirus–induced immunomodulation remains to be elucidated (27).

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Figures

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Figure 1.
Severe acute respiratory syndrome epidemic curve in Hong Kong, 2003, by infection cluster.
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Figure 2.
Geospatial distribution of cases of severe acute respiratory syndrome in Hong Kong (February to June 2003).

Source: Hong Kong Department of Health.

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Grahic Jump Location
Figure 3.
Age and sex distributions of patients with severe acute respiratory syndrome (SARS) compared with the Hong Kong general population.

The solid and dotted lines refer to the proportion of the general population, and the bars refer to the proportion of all SARS cases.

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Grahic Jump Location
Figure 4.
Estimate of time from infection to onset distribution.

Note that this graph was based on data from a small subgroup of patients fitted to a γ distribution.

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Grahic Jump Location
Figure 5.
Estimates of onset-to-admission, onset-to-death, and onset-to-discharge distributions.

Estimates of time-dependent onset-to-admission distribution as a function of time of onset of clinical symptoms (top), onset-to-death distribution by patients' age (middle), and onset-to-discharge distribution by patients' age (bottom). The kernel density for the intervals from onset to admission, onset to death, and onset to discharge were plotted by using the Gaussian kernel (21).

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Figure 6.
Nonparametric probabilities of survival and discharge.
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Appendix Figure 1.
Estimates of onset-to-admission, onset-to-death, and onset-to-discharge distributions.

Estimates of time-dependent onset-to-admission distribution as a function of time of onset of clinical symptoms (top), onset-to-death distribution by patients' age (middle), and onset-to-discharge distribution by patients' age (bottom). The kernel density for the intervals from onset to admission, onset to death, and onset to discharge were plotted by using the Gaussian kernel (21).

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Grahic Jump Location
Appendix Figure 2.
Nonparametric probabilities of survival and discharge.
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Summary for Patients

Description of the 2003 Severe Acute Respiratory Syndrome Outbreak in Hong Kong

The summary below is from the full report titled “The Epidemiology of Severe Acute Respiratory Syndrome in the 2003 Hong Kong Epidemic: An Analysis of All 1755 Patients.” It is in the 2 November 2004 issue of Annals of Internal Medicine (volume 141, pages 662-673). The authors are G.M. Leung, A.J. Hedley, L.-M. Ho, P. Chau, I.O.L. Wong, T.Q. Thach, A.C. Ghani, C.A. Donnelly, C. Fraser, S. Riley, N.M. Ferguson, R.M. Anderson, T. Tsang, P.-Y. Leung, V. Wong, J.C.K. Chan, E. Tsui, S.-V. Lo, and T.-H. Lam.

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