Body Heat Spreads Influenza

WHO declares H1N1 influenza virus pandemic.
Jason Socrates Bardi, Editor

(Inside Science) -- Yesterday the World Health Organization (WHO) officially declared the new strain of H1N1 influenza virus to be a pandemic after 74 countries reported nearly 30,000 confirmed cases -- about half of which are in the United States. New studies are emerging that show how the flow of air in a room and our own body heat influence the spread of the disease.

"The world is now at the start of the 2009 influenza pandemic," WHO Director-General Margaret Chan said in a press conference yesterday. "Further spread is considered inevitable."

Scientists seeking to understand how this spread occurs know that the H1N1 strain, like all influenza viruses, is transmitted when a sick person coughs or sneezes infectious droplets into the air. What happens to these droplets next depends on the type of room a person is in and the number and location of people in the room.

Humans generate a lot of heat, which can affect the spread of H1N1 influenza and other infections through the air, even in a calm indoor environment. Experts say this happens because body heat creates thermal plumes that move the air around us. These plumes profoundly influence what enters our breathing zone -- the six to eight inches of space around the mouth.

"[A] thermal plume acts like a pump to bring the nasties from your feet into your breathing zone," said Syracuse University professor Mark Glauser. Recently, he published a study using manikins seated across a table from each other that were designed to put out human levels of heat. The study showed that the exchange of air between the manikins' breathing zones was driven more by body heat than the airflow in the room. Glauser is the 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.

If you are sitting across from someone, your own body heat can create thermal plumes that draw in the particles they expel from three feet away or more, said Glauser. When asked if there is some distance at which the thermal plumes do not interact, Glauser replied, "We don't know that yet for sure since it depends on the type of ventilation system and corresponding airflows. For example, for the ventilation system setup in our two manikin studies, the results show interaction between the plumes as far away as 1.5 – 2 meters."

What we do know, he added, is that there are ways to make our breathing zones safer by improving the airflow in enclosed spaces. One such solution is displacement ventilation, in which air moves from an outflow in one part of the room (the floor, for instance) to an intake in another location (like the ceiling).

Many hospitals use displacement ventilation to keep diseases from spreading through the hospital, said John Cimbala of Pennsylvania State University in College Station, who studies the transport of pathogens in the air. "Warm air rises, and if air is blown down from the ceiling, it fights the tendency of the air to go up.”

This is a big problem in factory farm poultry enclosures, where a single building may contain more than 150,000 birds, and in other buildings that contain livestock, added Cimbala. According to his calculations, a sick chicken in one corner can contaminate the whole building. Contamination can spread from building to building within a compound if the exhaust from a contaminated building is released upwind of another building.

At Purdue University in West Lafayette, IN, fluid dynamicist Qingyan Chen has shown that displacement ventilation is a better way of providing air to some types of indoor settings such as office spaces. "In cubicles using this kind of ventilation," he said, "the possibility of being infected by a colleague is greatly reduced."

An even more futuristic approach may be to design intelligent personalized ventilation systems that can deliver clean air in a jet from a distance to refresh breathing zones and allow individuals to control their own environments.

"It's all about moving air in different ways," said Glauser.

 

Author Bio & Story Archive

Jason Socrates Bardi is the former News Director of the American Institute of Physics and a longtime science writer.