Predicting Which Patients Have Severe Acute Respiratory Syndrome

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The summary below is from the full report titled "A Clinical Prediction Rule for Diagnosing Severe Acute Respiratory Syndrome in the Emergency Department." It is in the 7 September 2004 issue of Annals of Internal Medicine (volume 141, pages 333-342). The authors are G.M. Leung, T.H. Rainer, F.-L. Lau, I.O.L. Wong, A. Tong, T.-W. Wong, J.H.B. Kong, A.J. Hedley, and T.-H. Lam, for the Hospital Authority SARS Collaborative Group.

What is the problem and what is known about it so far?

Severe acute respiratory syndrome (SARS) is a serious, sometimes fatal, illness caused by a virus called a coronavirus. The illness was first described in Asia in 2003. It was discovered in Chinese patients who had fever and severe breathing problems. In the spring of 2003, SARS quickly spread among humans with close person-to-person contact. More than 8000 people in Asia, Europe, and North and South America developed SARS. Some areas, such as Hong Kong, set up emergency clinics to handle the large numbers of patients with the illness. Because SARS is a newly discovered illness, doctors do not always know how to distinguish it from other viral illnesses, such as influenza.

Why did the researchers do this particular study?

To find a practical way of identifying persons with low and high probabilities of having SARS.

Who was studied?

2649 patients seen at 2 Hong Kong triage clinics during the 2003 SARS epidemic.

How was the study done?

The researchers reviewed medical records of the patients who visited SARS triage clinics in the emergency departments of 2 Hong Kong hospitals in 2003. Specifically, they reviewed standard forms that had been used to record patients' presenting symptoms, physical findings, chest radiography results, and blood work results. The researchers also reviewed records to see which patients had blood test results that confirmed SARS. They analyzed these data to see which presenting features were associated with increased and decreased probabilities of finding SARS. Then, they used a risk index to score characteristics that helped identify or rule out SARS. Finally, they tested the ability of the risk index to correctly identify patients with SARS.

What did the researchers find?

Several features increased the likelihood of SARS: previous contact with a patient with SARS, fever, myalgia (muscle aches), malaise (feeling weak), abnormal chest radiograph, and abnormal lymphocyte and low platelet counts. Age older than 65 years or younger than 18 years, sputum production, abdominal pain, sore throat, runny nose, and high neutrophil count decreased the likelihood of SARS. The index that scored the presence or absence of these characteristics identified patients with low (<5%), high (20% to 40%), and very high (60% to 80%) probabilities of having SARS.

What were the limitations of the study?

Study data were obtained by reviewing medical records. Some patients may have had symptoms and findings that were not recorded in the records. Characteristics that identify patients with a high likelihood of SARS may be different in settings that are not large outbreaks.

What are the implications of the study?

A risk index that used data easily obtained in emergency departments identified patients with low and high likelihood of SARS during an outbreak.