Evaluation of WHO criteria for identifying patients with severe acute respiratory syndrome

Evaluation of WHO criteria for identifying patients with severe acute respiratory syndrome out of hospital: prospective observational study

To determine the clinical and radiological features of severe acute respiratory syndrome (SARS) and to evaluate the accuracy of the World Health Organization's guidelines on defining cases of SARS.

A newly set up SARS screening clinic in the emergency department of a university hospital in Hong Kong's New Territories.

556 hospital staff, patients, and relatives who attended the screening clinic and who had had contact with someone with SARS. Main outcome measure Number of confirmed cases of SARS.

Of the 556 people, 141 were admitted to hospital, and 97 had confirmed SARS. Fever, chills, malaise, myalgia, rigor, loss of appetite, vomiting, diarrhoea, and neck pain but not respiratory tract symptoms were significantly more common among the 97 patients than among the other patients. The overall accuracy of the WHO guidelines for identifying suspected SARS was 83% and their negative predictive value was 86% (95% confidence interval 83% to 89%). They had a sensitivity of 26% (17% to 36%) and a specificity of 96% (93% to 97%).

Current WHO guidelines for diagnosing suspected SARS may not be sufficiently sensitive in assessing patients before admission to hospital. Daily follow up, evaluation of non-respiratory, systemic symptoms, and chest radiography would be better screening tools. Initial reports on severe acute respiratory syndrome (SARS) described the clinical features of confirmed cases.1–4 Later reports have described the epidemiology and progression of the illness in greater detail.5 6

On the basis of early findings in hospitals, the World Health Organization and the Hospital Authority of Hong Kong produced case definitions for suspected and probable cases of SARS that may be used for screening patients before admission to hospital and in non-clinical contexts such as airports.7 8 The discovery of the virus and the development of rapid serological tests may improve case definition, but the tests are not yet widely available.9–11

In the first two weeks of March 2003, 15 doctors, 15 nurses, 17 medical students, and five other staff (auxiliary staff, a clerk, and cleaning staff) associated with ward 8A of the Prince of Wales Hospital were infected with SARS. In response to this outbreak the hospital set up an emergency screening clinic on 12 March to evaluate all staff and their immediate contacts. The clinic gave us the opportunity to study the clinical response to the virus in a high contact environment.

We investigated the clinical features of SARS in the early stages of infection to evaluate the WHO criteria for identifying suspected and probable cases of SARS and to report the safety of our current strategies to prevent the spread of SARS among our staff.

"The current definitions allow authorities to rule out a case if another reasonable diagnosis is discovered. The North York and Grey Bruce cases suggest that that's no longer an option, Low said, noting that 10 to 15 per cent of community acquired pneumonias are caused by more than one agent. "It's naive to think to think that people only have infection with one organism. It's naive to think that because somebody has influenza B that they couldn't have SARS," he said. Since the SARS outbreak began, the Winnipeg lab has been working overtime, processing samples submitted from about 2100 people so far."

Henry L Niman, PhD
Instructor in Surgery (Bioengineering)
Harvard Medical School
51 Blossom Street, Room 422
Boston, MA 02114 USA
<henry_niman@hms.harvard.edu

(Many details are unavailable from this newswire report: the methodology of testing (presumably serology, IgM, IgG?, threshold for positivity), the denominator (that is, the total number of tests done of which 120 were positive), the population from which they were drawn (community-acquired atypical pneumonia cases?), any contact or clinical data, and so forth. While the law of parsimony is often cited in clinical medicine, it is true that it is very possible to have multiple simultaneous infections -- indeed some respiratory infections predispose to others. It is also likely that a proportion of these are false positive tests and that some represent true infection. ProMED-mail awaits further details. - Mod.LM]

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