Epidemiological determinants of spread of causal agent of severe acute respiratory syndrome in Hong Kong.
BACKGROUND
Health authorities worldwide, especially in the Asia Pacific region, are seeking effective public-health interventions in the continuing epidemic of severe acute respiratory syndrome (SARS). We assessed the epidemiology of SARS in Hong Kong.


METHODS
We included 1425 cases reported up to April 28, 2003. An integrated database was constructed from several sources containing information on epidemiological, demographic, and clinical variables. We estimated the key epidemiological distributions: infection to onset, onset to admission, admission to death, and admission to discharge. We measured associations between the estimated case fatality rate and patients' age and the time from onset to admission.


RESULTS
After the initial phase of exponential growth, the rate of confirmed cases fell to less than 20 per day by April 28. Public-health interventions included encouragement to report to hospital rapidly after the onset of clinical symptoms, contact tracing for confirmed and suspected cases, and quarantining, monitoring, and restricting the travel of contacts. The mean incubation period of the disease is estimated to be 6.4 days (95% CI 5.2-7.7). The mean time from onset of clinical symptoms to admission to hospital varied between 3 and 5 days, with longer times earlier in the epidemic. The estimated case fatality rate was 13.2% (9.8-16.8) for patients younger than 60 years and 43.3% (35.2-52.4) for patients aged 60 years or older assuming a parametric gamma distribution. A non-parametric method yielded estimates of 6.8% (4.0-9.6) and 55.0% (45.3-64.7), respectively. Case clusters have played an important part in the course of the epidemic.


CONCLUSIONS
Patients' age was strongly associated with outcome. The time between onset of symptoms and admission to hospital did not alter outcome, but shorter intervals will be important to the wider population by restricting the infectious period before patients are placed in quarantine.
Donnelly
Christl A
CA
Department of Infectious Disease Epidemiology, Imperial College, London, UK. c.donnelly@imperial.ac.uk <c.donnelly@imperial.ac.uk>
Ghani
Azra C
AC
Leung
Gabriel M
GM
Hedley
Anthony J
AJ
Fraser
Christophe
C
Riley
Steven
S
Abu-Raddad
Laith J
LJ
Ho
Lai-Ming
LM
Thach
Thuan-Quoc
TQ
Chau
Patsy
P
Chan
King-Pan
KP
Lam
Tai-Hing
TH
Tse
Lai-Yin
LY
Tsang
Thomas
T
Liu
Shao-Haei
SH
Kong
James H B
JH
Lau
Edith M C
EM
Ferguson
Neil M
NM
Anderson
Roy M
RM
D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D002648:Child; D002675:Child, Preschool; D004196:Disease Outbreaks / Q000706:statistics & numerical data*; D018450:Disease Progression; D005260:Female; D006723:Hong Kong / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D007223:Infant; D016013:Likelihood Functions; D008297:Male; D008875:Middle Aged; D011790:Quarantine / Q000379:methods / Q000706:statistics & numerical data; D045169:Severe Acute Respiratory Syndrome / Q000175:diagnosis / Q000453:epidemiology*; D015996:Survival Rate