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Airborne SARS transmission possible -- study
Updated: 2005-03-24 10:20

Two new studies present evidence that the virus causing severe acute respiratory syndrome (SARS) may spread through the air, not just through direct contact with contaminated water droplets as previous research had shown, the Infectious Diseases Association of America (IDSA) reported on Wednesday.

SARS coronavirus was detected in the air in a patient's room during the 2003 outbreak in Toronto, according to the Canadian study. The Hong Kong study shows patients in hospital bays near a SARS patient had a much higher infection rate than patients in distant bays, consistent with the possibility of airborne SARS transmission.

In the Hong Kong study, which focused on the 2003 SARS outbreak at the Prince of Wales Hospital, 41 percent of patients admitted to the ward in which the first SARS patient was staying became infected.

Proximity to the bed of the first case seemed to be strongly linked with two-thirds of patients in the same bay infected and half of patients in an adjacent bay were infected with SARS, while only 18 percent of patients in distant bays were infected.

The researchers at the Chinese University of Hong Kong speculated that the increased risk of infection with closer proximity to the index SARS case suggests airborne transmission. Although they do not have "direct proof" of airborne transmission.

"No other known routes of infectious diseases transmission could adequately explain the spread of the disease in the outbreak, and hence we feel that the evidence is quite strong," the researchers wrote.

The Canadian research was conducted during the SARS outbreak in Toronto in March 2003. The results mark the first experimental confirmation of the presence of the SARS virus in the air of an infected patient's hospital room.

The authors cautioned that their results do not document any cases of airborne transmission of the SARS virus from one person to another, only the dissemination of the virus from an infected patient to the air, via breathing or coughing.

During the outbreak in Toronto hospitals, health care workers became infected with the virus despite observance of strict infection control precautions. The investigators wondered whether environmental contamination of hospital air or surfaces could explain the ongoing risk of SARS coronavirus transmission to health care workers.

To answer this question, they collected patient information and environmental samples from the SARS units of four Toronto hospitals.

SARS coronavirus was detected in the air in one of the four rooms tested. The researchers also detected virus in four of 85 surface samples taken from frequently touched surfaces, highlighting the importance of strict adherence to infection control precautions to prevent SARS coronavirus transmission in the health care setting.

An editorial accompanying the Toronto study, by Tommy Tong of Princess Margaret Hospital in Hong Kong, China, emphasized the scientific significance of discovering SARS coronavirus in the air in a patient's room.

"Although the possibility of airborne dissemination of SARS coronavirus has been controversial," he wrote, "this important work shows beyond doubt that SARS coronavirus aerosol generation can occur from a patient with SARS."

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