ALEXANDRIA, Va. -- Like other viral illnesses, SARS coronavirus infection can present with only mild symptoms, according to a study published in the Feb. 15, 2004 issue of The Journal of Infectious Diseases, online now. The findings help to flesh out the clinical portrait of this novel illness, which emerged in 2003 as a syndrome in which fever and mylagia progressed rapidly to pneumonia and respiratory distress, prompting its initial designation of SARS, or severe acute respiratory syndrome. One implication of the current study is that early detection of future SARS-associated coronavirus outbreaks will require attention to the mild end of the disease's spectrum.
The study, reported by Khek-Yu Ho, PA, Tambyah, and coworkers in Singapore, involved 372 healthcare workers at a large teaching hospital where 21 patients with SARS (including five of the hospital's staff) were treated. A questionnaire was used to determine which workers had had direct contact with SARS patients, which had no direct contact but were exposed, and which were not exposed. Subjects provided serum samples at the time of possible SARS exposure and a median of 31 days later; the samples were then screened for SARS antibodies using an enzyme-linked immunosorbent assay or a dot-blot immunoassay, and those with positive results were confirmed by an indirect immunofluorescence assay and a virus neutralization assay.
The investigators reported that none of the 260 hospital workers classified as not exposed was seropositive for the virus. Of 112 classified as exposed, eight were seropositive. Four of the eight had had direct contact with SARS-infected patients; the others had been in wards where SARS patients had been before transfer to a SARS facility. All eight had fever, but only six also had radiographic evidence of pneumonia and thus met clinical criteria for SARS. Symptoms in the two mildly infected subjects included chills and myalgia or cough, all of which resolved within three days of symptomatic therapy.
Noting that the vast majority of SARS cases thus far reported have occurred in hospitals, the Singapore investigators characterized their study as the first to demonstrate the infection in health care workers with normal chest X-rays. They pointed out that both clinical SARS and milder illness developed in those who were exposed to but not in direct contact with infected patients, suggesting that infection can occur regardless of the intensity of exposure. On the other hand, there was no disease transmission involving health care workers who were in other areas of the hospital. Moreover, no secondary transmission involving the two subjects with mild disease was seen. The investigators cautioned that although mildly symptomatic cases may reflect transmission of low viral loads that are unlikely to spark epidemics, such cases may remain "below the radar" if not actively sought with sensitive assays.
Source: Infectious Diseases Society of America