Single sneeze can fill room with flu virus for hours

A single sneeze from an infected person can leave virus particles suspended in the air for hours, a new study has found.

It is well known that sneezes and coughs play a part in spreading diseases which are able to survive outside the body. Until now it had been assumed that this is mostly through direct contact, i.e. by breathing in air droplets at the time of the sneeze or by touching surfaces on which the air droplets have settled.

But, as lead scientist Lindsey Marr from Virginia Tech explains: "The relative importance of the airborne route in influenza transmission—in which tiny respiratory droplets from infected individuals are inhaled by others—is not known."

What is known is that influenza A viruses are "transmitted through direct contact, indirect contact, large respiratory droplets, and aerosols that are left behind by the evaporation of larger droplets."

But this last form of infection is controversial "partly due to the difficulties in studies involving human subjects and partly due to the challenges in detecting influenza A viruses in ambient air" said Ms Marr.

Particle size is key

The key factor is the size of particles produced by the sneeze. If they are small enough then they can remain suspended in the air for some time.

To test this, the researchers collected samples from a waiting room of a health care centre, two toddlers' rooms and one babies' area of a day care centre and also three aeroplane flights.

Half of the samples collected contained aerosolized influenza A viruses in concentrations such that "the amount of viruses a person would inhale over one hour would be adequate to induce infection."

Based on estimated breathing rates and the amount of virus present, the study authors concluded that there would be sufficient virus present to induce infection.

The results of the study are published in the Journal of the Royal Society Interface.

This article was published on Wed 2 February 2011