Volume 29-13
1 July 2003

[Table of Contents]

Figure 2. Number* of reported cases of severe acute respiratory syndrome, by source of infection and date of illness onset - Toronto Canada, 15 April to 9 June, 2003

* N=74.

Editorial Note 

On 14 May, 2003, the WHO removed Toronto from the list of areas with recent local SARS transmission because 20 days (i.e. twice the maximum incubation period) had elapsed since the most recent case of locally acquired SARS was isolated or a SARS patient had died, suggesting that the chain of transmission had terminated. Before recognition of the second phase of the outbreak, the most recent case of locally acquired SARS in Toronto had been reported before 20 April. However, unrecognized transmission, limited initially to patient-to-patient and patient-to-visitor transmission, was apparently continuing in hospital A. After directives for increased hospital-wide infection control precautions had been lifted, an increase in the number of cases was observed, particularly among HCWs. 

The findings from this investigation underscore the importance of controlling health care associated SARS transmission and highlight the difficulty in determining when expanded precautions for SARS are no longer necessary. Investigations in Canada and other countries have identified HCWs to be at increased risk of SARS, and methods for performing surveillance among HCWs have been recommended⁽²⁾. The Toronto investigation suggests that unrecognized patient-to-patient and patient-to-visitor transmission of SARS might have been occurring with no associated cases of HCW illness until after a province-wide lifting of the expanded precautions for SARS. Transient carriage of pathogens on the hands of HCWs is the most common form of transmission for several nosocomial infections, and both direct contact and droplet spread appear to be major modes of SARS-CoV transmission⁽³⁾. HCWs should be directed to use gloves appropriately (e.g. change gloves after every patient contact and avoid their use outside a patient's room) and to pay scrupulous attention to hand hygiene before putting on and after removing gloves.

In addition to active and passive surveillance for fever and respiratory symptoms among HCWs, early detection of SARS cases among people in health care facilities in SARS-affected areas is critical, particularly in facilities that provide care to SARS patients. Identifying hospitalized patients with SARS is difficult, especially when no epidemiologic link has been recognized and the presentation of symptoms is nonspecific. Patients with SARS might develop symptoms common to hospitalized patients (e.g. fever or prodromal symptoms of headache, malaise, and myalgias), and diagnostic testing to detect cases is limited. Available nucleic acid amplification assays for SARS-CoV have reported sensitivities as low as 50%⁽⁴⁾. Although serologic testing for SARS-CoV antibody is available, definitive interpretation of an initial negative test requires a convalescent specimen to be obtained > 21 days after onset of symptoms⁽⁵⁾.

Several potential approaches for monitoring patients might improve recognition of SARS in hospitalized patients. A standardized assessment for SARS (e.g. clinical, radiographic, and laboratory criteria) might be used among all hospitalized patients with fever of new onset, especially for units or wards in which clusters of febrile patients are identified. In addition, some hospital computer information systems might allow review of administrative and physician order data to monitor selected observations that might serve as triggers for further investigation.

The Toronto investigation found early transmission of SARS to both patients and visitors in hospital A. In areas affected recently by SARS, clusters of pneumonia occurring in either visitors to health care facilities or HCWs should be evaluated fully to determine whether they represent transmission of SARS. To facilitate detection and reporting, clinicians in these areas should be encouraged to obtain a history from pneumonia patients of whether they visited or worked at a health care facility and whether family members or close contacts are also ill. Targeted surveillance for community-acquired pneumonia in areas recently affected by SARS might provide another means of early detection of these cases.

The findings from the Toronto investigation indicate that continued transmission of SARS can occur among patients and visitors during a period of apparent HCW adherence to expanded infection control precautions for SARS. Maintaining a high level of suspicion for SARS on the part of health care providers and infection control staff is critical, particularly after a decline in reported SARS cases. The prevention of health care associated SARS infections must involve HCWs, patients, visitors, and the community.

References 

1.    Poutanen SM, Low DE, Henry B et al. Identification of severe acute respiratory syndrome in Canada. N Engl J Med 2003;348(20):1995-2005. 

2.    CDC. Interim domestic guidance for management of exposures to severe acute respiratory syndrome (SARS) for health-care settings. URL: <http://www.cdc.gov/ncidod/sars/exposureguidance.htm>. 

3.    Seto WH, Tsang D, Yung RW et al. Effectiveness of precautions against droplets and contact in prevention of nosocomial transmission of severe acute respiratory syndrome (SARS). Lancet 2003;361:1519-20. 

4.    Peiris JS, Lai ST, Poon LL et al. Coronavirus as a possible cause of severe acute respiratory syndrome. Lancet 2003;361:1319-25. 

5.    Stohr K. A multicentre collaboration to investigate the cause of severe acute respiratory syndrome. Lancet 2003;361:1730-33. 

Source:    SARS Investigation Team, CDC; T Wallington, MD, L Berger, MD, B Henry, MD, R Shahin, MD, B Yaffe, MD, Toronto Public Health; B Mederski, MD, G Berall, MD, North York General Hospital; M Christian, MD, A McGeer, MD, D Low, MD, University of Toronto; Ontario Ministry of Health and Long-term Care, Toronto. T Wong, MD, T Tam, MD, M Ofner, L Hansen, D Gravel, A King, MD, Health Canada, Ottawa. 

[Table of Contents][Next]