A sick person talking quietly for five minutes, for instance, can expel roughly the same number of droplets as a cough. Many normal activities - laughing, talking, even just sitting still and quietly breathing - can increase the risk of infection spreading. A few years ago, he published a computer simulation study of a cough.Ĭoughing and sneezing aren't the only problem, said Zhu. A person sitting across a table from someone who coughs might inhale hundreds - or even thousands - of microscopic droplets, said Shengwei Zhu of Harvard University in Cambridge, MA. Scientists also measure and track these droplets as they move around a room with the air. Other researchers have used high-speed photography to capture the flying droplets of a sneeze. 'If it is not obstructed, it forms a jet that penetrates a meter or more into the surrounding air.' Settles photographed and measured cough plumes last year and published them in the New England Journal of Medicine. 'A cough comes squirting out,' said Gary Settles, a fluid dynamicist at Pennsylvania State University in State College. Many 'fluid dynamicists' like Glauser are studying the question of how influenza spreads physically, using the same methods scientists use to study the flow of air over wind turbines or water through a propeller. 'Fluid mechanics is extremely important in the transport of these things,' said Syracuse University professor Mark Glauser, associate director of a $40 million dollar research program funded by the Environmental Protection Agency and New York State that looks at the exposure and risks of contaminants in indoor environments. These droplets can float along until they enter someone else's breathing zone - the space up to six or eight inches away from the mouth. When sick people cough, sneeze, laugh, or talk, they spread thousands of droplets containing as many as hundreds of millions of infectious particles into the air. But in any enclosed environment, a sick person can still infect others. This practical public health measure, called 'social distancing,' is one of the best ways to contain an outbreak of infection. The Centers for Disease Control and Prevention (CDC) recommends avoiding contact with someone who has influenza-like symptoms. We spend more than half our days at home and most of the rest of the time moving between offices, restaurants, stores, buses, cars, subways, and other enclosed environments. Most people in the United States spend the majority of their lives indoors - more than 90 percent of their time according to several studies. Part of the answer lies in asking how safe the air we breathe is. (Inside Science) - Now that the World Health Organization (WHO) has declared the new strain of influenza to be the cause of a pandemic, the question people will be asking more than ever is: how can we make ourselves safer?

The breathing zone