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.

Researchers in Hong Kong, mainland China and Canada published two papers in the May 1 edition of The Journal of Infectious Diseases, which is sponsored by the IDSA.

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 patient seemed to be strongly linked, with two-thirds of patients in the same bay infected and half of patients in an adjacent bay infected with SARS. Only 18 percent of patients in distant bays were infected.

The researchers, led by Ignatius T.S. Yu of the Chinese University of Hong Kong, speculate that the increased risk of infection with closer proximity suggests airborne transmission.

Dr. Yu said that they lack direct proof of airborne transmission, but they feel the evidence is "quite strong" because "no other known routes of infectious diseases transmission could adequately explain the spread of the disease in the outbreak."

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 emphasized 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, speculating that environmental contamination of hospital air or surfaces might explain the ongoing risk, collected patient information and environmental samples from the SARS units of four Toronto hospitals.

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

An editorial accompanying the Toronto study, by Tommy Tong of Princess Margaret Hospital in Hong Kong, 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."

(Xinhua News Agency March 24, 2005)