Epidemiology and Infection

Research Article

Duration and distance of exposure are important predictors of transmission among community contacts of Ontario SARS cases

E. REAa1a5, J. LAFLÈCHEa1, S. STALKERa2, B. K. GUARDAa3, H. SHAPIROa4, I. JOHNSONa5, S. J. BONDYa5, R. UPSHURa5, M. L. RUSSELLa6 c1 and M. ELIASZIWa6a7

a1 Toronto Public Health, Toronto, ON, Canada

a2 York Region Health Services, Newmarket, ON, Canada

a3 Simcoe Muskoka District Health Unit, Barrie, ON, Canada

a4 Region of Peel Public Health, Brampton, ON, Canada

a5 Public Health Sciences, University of Toronto, Toronto, ON, Canada

a6 Department of Community Health Sciences, University of Calgary, Alberta, Canada

a7 Department of Clinical Neurosciences, University of Calgary, Alberta, Canada

SUMMARY

We report attack rates and contact-related predictors among community contacts of severe acute respiratory syndrome (SARS) cases from the 2003 Toronto-area outbreak. Community contact data was extracted from public health records for single, well-defined exposures to a SARS case. In total, 8662 community-acquired exposures resulted in 61 probable cases; a crude attack rate of 0·70% [95% confidence interval (CI) 0·54–0·90]. Persons aged 55–69 years were at higher risk of acquiring SARS (1·14%) than those either younger (0·60%) or older (0·70%). In multivariable analysis exposures for at least 30 min at a distance of xs2A7D1 m increased the likelihood of becoming a SARS case 20·4-fold (95% CI 11·8–35·1). Risk related to duration of illness in the source case at time of exposure was greatest for illness duration of 7–10 days (rate ratio 3·4, 95% CI 1·9–6·1). Longer and closer proximity exposures incurred the highest rate of disease. Separate measures of time and distance from source cases should be added to minimum datasets for the assessment of interventions for SARS and other emerging diseases.

(Accepted November 10 2006)

(Online publication January 12 2007)

Correspondence:

c1 Author for correspondence: Dr M. Russell, Department of Community Health Sciences, 3330 Hospital Dr NW, Calgary, Alberta, Canada T2N 4N1. (Email: mlrussel@ucalgary.ca)

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