You never want to sit next to that guy during flu season.
You know, the snivelling, sneezing, hacking sort who occupies the desk beside you or the neighbouring seat on the plane. It's just a matter of time before they infect you with whatever crud's going around.
Except, a new study suggests, it's not the tissue-groping, say-it-don't-spray-it types that are most likely to get you. All a sickly person really has to do is breathe around you.
Researchers at the University of Maryland tested the exhaled breath of 38 flu patients and checked both large droplets and fine airborne particles for flu virus. It turned out that the fine airborne particles - released by normal breathing - contained nearly nine times more virus than larger droplet particles released when a person coughs and sneezes. The study was published March 7 in the journal PLOS Pathogens.
The team - led by Dr Donald Milton, director of the Maryland Institute of Applied Environmental Health - used a machine dubbed "The Gesundheit II'' to collect samples from each volunteer for 30 minutes. Some people sitting at the machine released undetectable levels of virus; others put out over 100,000 viruses during the test.
The researchers also tested some of the patients while they wore paper surgical masks, recommended by the US Centers for Disease Control and Prevention as a way to prevent someone with the flu from spreading the virus. In the study, the masks reduced the amount of virus shed by 3.4 times overall.
It's also good to know that if you must share a space with someone who has the flu, you're better off if the room is somewhat humid.
Researchers at the CDC's National Institute for Occupational Safety and Health reported in late February that the viral load in a dry room was more than five times greater than the amounts found in a room with greater humidity. Their report appeared in the journal PLOS One.
An hour after virus particles were released in a room with a relative humidity of 23 per cent or less (typical in many spaces during a winter heating season) up to 77 per cent were still infectious. But when the humidity was increased to 43 per cent, only about 14 per cent of the virus particles were capable of infecting. Most of the inactivation occurred within 15 minutes of the virus being released in the more humid room.
Experts say the optimal humidity range is between 30 and 50 per cent to avoid health problems with breathing and nosebleeds during the winter.