Fresh Air Blows Cold Germs Away

The more outdoor air is pumped into office ventilation systems, the lower the inside levels of viruses that cause the common cold -- according to a new report.

Few studies have considered the possible link between the ventilation of buildings and respiratory illness in their occupants, note the authors of the study in the American Journal of Respiratory and Critical Care Medicine.

Dr. Donald K. Milton from Harvard School of Public Health in Boston, Massachusetts, and colleagues sampled the workday air from three office buildings and used molecular techniques to detect and identify rhinoviruses in air samples and in nasal mucus from building occupants.

The concentration of carbon dioxide in the air was used as a measure of exhaled breath and the supply rate of outdoor air.

There was a significant relationship between the detection of airborne rhinoviruses and the amount of stale indoor air, the investigators report.

Also, one rhinovirus present in a nasal mucus sample from an occupant with a cold proved to be identical to a rhinovirus collected on an air filter from the same building during the occupant's illness, the team notes.

"These data suggest that lower ventilation rates and resulting increased carbon dioxide concentrations are associated with increased risk of exposure to potentially infectious droplets," Milton's team concludes.

"Although this study does not provide definitive proof that rhinovirus is transmitted through the aerosol route and is modulated by outdoor air supply rates," they add, "it does provide support for this hypothesis."

"The findings...of increasing virus detection with rising carbon dioxide concentration indicates one possibility for reducing transmission -- increasing exchange of indoor with outdoor air," writes Dr. Jonathan M. Samet from Johns Hopkins University in Baltimore, Maryland in a related editorial.

Samet agrees with Milton's group that other environments, "particularly schools" should be investigated in the same way.

SOURCE: American Journal of Respiratory and Critical Care Medicine, June 1, 2004.

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