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The SARS epidemic: emergence of a new respiratory virus?
  1. T Seemungal
  1. 1Web editor, Thorax tseemungal{at}aol.com

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This clinical study of 138 patients from a Hong Kong hospital suggests that the severity of the severe acute respiratory syndrome (SARS) (intensive care and/or death) was associated with advanced age, high peak lactate dehydrogenase level (LDH), and an absolute neutrophil count that exceeded the normal range at presentation. 78% of patients had consolidation on the chest radiograph at initial consultation.

Nineteen inpatients (6 in Hong Kong, 1 in Canada, 10 in Vietnam, 1 in Taiwan, 1 not stated) with SARS were identified as being infected with the SARS coronavirus determined by virus isolation, reverse transcriptase polymerase chain reaction (RT-PCR), or serology. The virus sequence was obtained either from clinical specimens or virus isolates from 12 of these patients and amplified by RT-PCR for viral identification. None of the patients infected with the SARS coronavirus was infected with human metapneumovirus. Co-infection with another virus (rhinovirus) was found in one patient. Further genetic analysis showed the SARS coronavirus to be a new virus. Initial testing suggests that this virus may never before have infected the US population. A variety of respiratory pathogens were also identified by RT-PCR in patients whose samples were submitted for SARS testing, including 5 with human metapneumovirus and 13 with rhinovirus. None of the patients who were positive for human metapneumovirus had pneumonia.

This was a study of 50 cases of clinically diagnosed SARS from three hospitals in Hong Kong and 280 controls. Evidence of the SARS coronavirus (serology and/or viral RNA from nasopharyngeal aspirate or stool) was found in 45 patients but not in controls. Despite fever, 49 (98%) patients had no evidence of leucocytosis. Older age, severe lymphopenia, and impaired ALT were associated with increased severity of infection requiring intensive care and ventilatory support. Peak LDH was not measured. All patients had radiological evidence of consolidation on the chest radiograph.

This outbreak was a point source outbreak starting with a visitor from southern China on 21 February 2003. The disease spread rapidly from hospital health care workers to the community. Cumulative total cases during March 2003 were as follows: 14th (n=3), 21st (n=203), 26th (n=319), 31st (n=610). The authors suggest that the incubation period is 2–11 days; lymphopenia and liver dysfunction were found commonly in hospital admitted patients.

Comment

A new respiratory virus, the SARS coronavirus, appears to have been identified and we await further information on its source. The markers of severity of SARS are still unclear, but older age and impaired liver function appear to be consistent between the above studies. However, the clinical spectrum of this disease in the community (those patients not admitted to hospital) is still to be defined. An assessment of the severity of the syndrome in the presence or absence of detection of the SARS coronavirus may be of interest.

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