American Journal of Epidemiology Advance Access originally published online on May 10, 2007
American Journal of Epidemiology 2007 166(3):355-363; doi:10.1093/aje/kwm082
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PRACTICE OF EPIDEMIOLOGY |
Estimating Variability in the Transmission of Severe Acute Respiratory Syndrome to Household Contacts in Hong Kong, China
1 Department of Epidemiology, School of Public Health, Harvard University, Boston, MA
2 Department of Community Medicine, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong, China
3 Department of Immunology and Infectious Diseases, School of Public Health, Harvard University, Boston, MA
Correspondence to Virginia E. Pitzer, Department of Epidemiology, Harvard School of Public Health, 677 Huntington Avenue, Boston, MA 02115 (e-mail: vpitzer{at}hsph.harvard.edu).
Received for publication June 19, 2006. Accepted for publication February 5, 2007.
The extensive data collection and contact tracing that occurred during the 2003 outbreak of severe acute respiratory syndrome (SARS) in Hong Kong, China, allowed the authors to examine how the probability of transmission varied from the date of symptom onset to the date of hospitalization for household contacts of SARS patients. Using a discrete-time likelihood model, the authors estimated the transmission probability per contact for each day following the onset of symptoms. The results suggested that there may be two peaks in the probability of SARS transmission, the first occurring around day 2 after symptom onset and the second occurring approximately 10 days after symptom onset. Index patients who were aged 60 years or older or whose lactate dehydrogenase level was elevated upon admission to the hospital (indicating higher viral loads) were more likely to transmit SARS to their contacts. There was little variation in the daily transmission probabilities before versus after the introduction of public health interventions on or around March 26, 2003. This study suggests that the probability of transmission of SARS is dependent upon characteristics of the index patients and does not simply reflect temporal variability in the viral load of SARS cases.
communicable diseases, emerging; disease outbreaks; disease transmission; Markov chains; models, statistical; SARS virus; severe acute respiratory syndrome
Abbreviations: CI, credible interval; DIC, deviance information criterion; LDH, lactate dehydrogenase; SARS, severe acute respiratory syndrome