W.H.O. Broadens Definition of Airborne Diseases

In the early days of the Covid pandemic, a team of scientists called on the World Health Organization to acknowledge that the disease could spread through the air.

Initially, the agency rebuffed them, despite growing evidence that coronavirus-laden droplets stuck around in the air, making indoor spaces hotbeds of infection. The researchers responded with a public campaign, which helped persuade the World Health Organization to finally acknowledge, in late 2021, that Covid was airborne.

In the wake of the controversy, the agency also asked a group of advisers — including some of its scientific critics — to update its formal guidelines for classifying the ways that pathogens spread. After more than two years of discussion, that group has published a report laying out new definitions that could have significant implications for countries around the world that depend on the agency to set policies to curb the spread of disease.

The W.H.O.'s previous stance was that only a handful of pathogens — those that travel in small droplets and spread across long distances, like tuberculosis — could be considered airborne. But the new report suggests broader categories that do not rely on droplet size or distance spread. Such changes were contentious because they raised the prospect that more diseases might now demand costly control measures, such as hospital isolation rooms and protective gear.

"It's an important first step," said Dr. Ed Nardell, a tuberculosis expert at Harvard Medical School and a member of the group. "We really have a start, with agreed-upon terminology, even if everybody's not happy with it."

Before the pandemic, the W.H.O. and other agencies typically recognized a few ways diseases could spread. One was by "contact transmission," in which someone picked up a pathogen either by touching an infected person directly or through contact with a contaminated surface.

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