© 2003 Canadian Medical Association or its licensors
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Investigation of a nosocomial outbreak of severe acute respiratory syndrome (SARS) in Toronto, Canada
From the Canadian Field Epidemiology Program, Health Canada, Ottawa Ont. (Varia, Wilson, Sarwal, Galanis); Mount Sinai Hospital, Toronto, Ont. (McGeer); and Toronto Public Health, Toronto, Ont. (Gournis, Henry).Additional members of the Hospital Outbreak Investigation Team: Sheela Basrur, Michael Finkelstein, Faron Kolbe, Anna Miranda, Margaret Mulholland, Marjolyn Pritchard, Rita Shahin, Sharron Stone and Barbara Yaffe, Toronto Public Health, Toronto, Ont.; Linda Davis, Sandy Finkelstein, Grant Large and David Rose, Scarborough Hospital, Toronto, Ont.; Adrienne Chan, Donald Low, Matthew Muller and Elizabeth Rea, University of Toronto, Toronto, Ont.; Arlene King, Jeannette Macey and Theresa Tam, Division of Immunization and Respiratory Diseases, Health Canada, Ottawa Ont.; Karen Green and Margaret McArthur, Mount Sinai Hospital, Toronto, Ont.; Erika Bontovics and Colin D'Cunha, Ontario Ministry of Health and Long-Term Care, Toronto, Ont.; James Young, Ontario Ministry of Public Safety and Security, Toronto, Ont.; and Marianne Ofner, Blood Safety Surveillance and Health Care Acquired Infections Division, Health Canada, Ottawa, Ont.
Correspondence to: Dr. Bonnie Henry, Toronto Public Health, 277 Victoria St., Toronto ON M5B 1W2
Background: Severe acute respiratory syndrome (SARS) was introduced into Canada by a visitor to Hong Kong who returned to Toronto on Feb. 23, 2003. Transmission to a family member who was later admitted to a community hospital in Toronto led to a large nosocomial outbreak. In this report we summarize the preliminary results of the epidemiological investigation into the transmission of SARS between 128 cases associated with this hospital outbreak.
Methods: We collected epidemiologic data on 128 probable and suspect cases of SARS associated with the hospital outbreak, including those who became infected in hospital and the next generation of illness arising among their contacts. Incubation periods were calculated based on cases with a single known exposure. Transmission chains from the index family to hospital contacts and within the hospital were mapped. Attack rates were calculated for nurses in 3 hospital wards where transmission occurred.
Results: The cases ranged in age from 21 months to 86 years; 60.2% were female. Seventeen deaths were reported (case-fatality rate 13.3%). Of the identified cases, 36.7% were hospital staff. Other cases were household or social contacts of SARS cases (29.6%), hospital patients (14.1%), visitors (14.1%) or other health care workers (5.5%). Of the 128 cases, 120 (93.8%) had documented contact with a SARS case or with a ward where there was a known SARS case. The remaining 8 cases without documented exposure are believed to have had exposure to an unidentified case and remain under investigation. The attack rates among nurses who worked in the emergency department, intensive care unit and coronary care unit ranged from 10.3% to 60.0%. Based on 42 of the 128 cases with a single known contact with a SARS case, the mean incubation period was 5 days (range 2 to 10 days).
Interpretation: Evidence to date suggests that SARS is a severe respiratory illness spread mainly by respiratory droplets. There has been no evidence of further transmission within the hospital after the elapse of 2 full incubation periods (20 days).
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