Aerosol transmission could be a possible way in which influenza spreads, other than direct contact and droplets.
On April 4, 2008, seven inpatients in a Hong Kong hospital's general medical ward developed fever and respiratory symptoms. Eventually, nine inpatients exhibited influenza-like symptoms and tested positive for influenza A.
The cause of the outbreak was believed to be an influenza patient who received a form of non-invasive ventilation and was then moved to the intensive care unit after 16 hours.
During the time, he was located right beside the outflow jet of an air purifier, which created an unopposed air current across the ward.
"We showed that infectious aerosols generated by a respiratory device applied to an influenza patient might have been blown across the hospital ward by an imbalanced indoor airflow, causing a major nosocomial outbreak," said study author Nelson Lee of the Chinese University of Hong Kong.
"The spatial distribution of affected patients was highly consistent with an aerosol mode of transmission, as opposed to that expected from droplet transmission," he added.
"Suitable personal protective equipment, including the use of N95 respirators, will need to be considered when aerosol-generating procedures are performed on influenza patients," Lee added.
"Avoiding such procedures in open wards and improving ventilation design in health care facilities may also help to reduce the risk of nosocomial transmission of influenza."
The study is published in the current issue of Clinical Infectious Diseases.