The Clinical Features of SARS: Establishing a Diagnosis in the Absence of a Diagnostic Test
This is one of three Journal Notes this week that cover severe acute respiratory syndrome (SARS).
In March 2003, the World Health Organization (WHO) issued a global health alert regarding an atypical type of pneumonia that was appearing in Hong Kong, China and Vietnam. Since then, severe acute respiratory syndrome (SARS) has spread to more than 28 countries and, according to the World Health Organization (WHO), affected some 7,699 individuals.
As yet, there is no objective diagnostic test for this new syndrome. Therefore, in an effort to help physicians accurately identify SARS patients, WHO established a definition of a suspected case of SARS, which consisted of individuals with fever, cough or difficulty breathing, and contact with an individual believed to have SARS or to have been exposed to SARS. A probable case of SARS was defined as an individual who met all the criteria for a suspected case of SARS, and also showed x-ray evidence of pneumonia, respiratory distress, or unexplained respiratory illness.
Unfortunately, these case definitions rely heavily on the physician’s ability to establish a history of exposure to SARS. However, as the infection becomes more widespread, it will likely become more and more difficult to determine where a patient picked up the virus. Therefore, a group of researchers set out to describe the clinical characteristics of SARS in a way that does not rely on establishing a history of SARS exposure.
This early release study, which will be published in the June 4, 2003 issue of the Journal of the American Medical Association , found that a number of clinical features, including fever, cough, muscle pain, and difficulty breathing, may help physicians determine a diagnosis of SARS in the event that establishing a prior history of SARS exposure is not possible.
About the study
The researchers examined 144 cases of SARS in adult patients in the greater Toronto, Ontario area between March 7 and April 10, 2003. Most of these patients had been exposed to SARS in the healthcare setting (patients, health care workers, visitors) and most developed symptoms within approximately six days of exposure. These symptoms consisted primarily of fever, a known exposure to SARS, and respiratory symptoms or evidence of infection on chest x-ray.
The researchers examined where and how each patient was initially exposed to SARS, their medical histories, findings from their physical examinations and laboratory tests, and how they fared after 21-days (eg, death or admission to the ICU).
The researchers found that the most common clinical symptoms in this group of patients were:
- self-reported fever (99%)
- documented fever (85%)
- nonproductive (dry) cough (69%)
- muscular pain or tenderness (49%)
- difficulty breathing (42%)
Common laboratory findings included:
- elevated levels of a certain enzyme called lactate dehydrogenase (87%)
- low serum calcium levels (60%)
- reduced lymphocyte (immune cell) levels (54%)
These results are consistent with those found in a similar study involving ]]>SARS patients in Hong Kong]]> .
The study also found that a significant portion of the patients examined (25%) did not show suspicious findings on their x-rays at the time of admission, and would have been missed under the probable case definition currently supported by the WHO.
Researchers also discovered that among patients infected with SARS, the presence of diabetes and other comorbid conditions were independently associated with a poorer outcome (death, ICU admission, or mechanical ventilation) than those who did not have a comorbid condition.
How does this affect you?
Despite the fact that there is currently no simple, reliable test for the diagnosis of SARS, the results of this study suggest that there are certain clinical features that should alert physicians to the infection, even when a clear history of possible exposure cannot be determined. The most consistent features include self-reported or documented fever, dry cough, and elevated lactate dehydrogenase levels.
Based on these findings, the current case definitions supported by the WHO would have excluded a significant number of the Toronto SARS patients who presented with fever and contact history, but no respiratory symptoms or chest x-ray findings. This has important public health implications since patients could conceivably spread the infection if their fever was not immediately recognized as a sign of SARS.
An editorial accompanying the study commends the authors for developing their comprehensive description of the clinical features of SARS so quickly. However, the editorialist goes on to warn that the clinical presentation of SARS is consistent with a number of other respiratory illnesses caused by similar viruses and that the full spectrum of SARS symptoms may not yet be fully recognized or appreciated. Therefore, until a diagnostic test for SARS becomes available, physicians must be ever vigilant about identifying atypical presentations of the disease.
Centers for Disease Control and Prevention
World Health Organization
United States Department of Health and Human Services
Booth CM, Matukas LM, Tomlinson GA et al. Clinical features and short-term outcomes of 144 patients with SARS in the greater Toronto area. JAMA. 2003;289. Early release article.
Masur H, Emanuel E, Lane HC. Severe acute respiratory syndrome: providing care in the face of uncertainty. JAMA. 2003;289. Early release article.
Last reviewed May 16, 2003 by ]]>Richard Glickman-Simon, MD]]>
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