Where did the droplet/airborne distinction come from? It was based on observations regarding proximity. Most respiratory viruses, including the flu, are usually passed among people in relatively close contact.
But then there are pathogens like the measles virus, which can also infect people at greater distances: A U.S. measles outbreak in the 1990s, for example, happened at an international sports event held in a domed stadium.
The droplet-borne/airborne categories emerged to explain those differences in viral transmission.
However, Klompas said, it’s really other factors that are key — such as ventilation. Even airborne pathogens rapidly become “diluted” in a well-ventilated area, which lowers the risk of infection.
In a pandemic-era study of train passengers, people seated next to someone with an asymptomatic COVID-19 infection were 10 times as likely to become infected as passengers who were three seats away.
Poor ventilation, though, lowers the protection afforded by distance, Klompas said.
Related: Dane County Madison public health.