If You Are Germophobic, Don't Read This Article

Imagine you are riding the subway in New York City. Someone a few feet away from you coughs. He tries to cover his mouth, but he is holding a grocery bag and just coughs indirectly into his sleeve. Some of the cough is not contained and spreads out into the recirculated air of the subway car. You curse him under your breath and think "Great, I'm going to get sick."

Does this sound paranoid? Would you consider the person in this story to be a "germophobe?" I know I would. And it turns out I'd be wrong.

In fact, all passengers stand a good chance of being infected with whatever bacteria is in the small droplets of saliva and bacteria that just escaped from this man's mouth. 

It is some of the oldest health advice ever given to you: "Cover your mouth when you sneeze or cough." Now researchers are showing just how important this piece of advice can be when trying to keep diseases from spreading. 

"We wanted to find out how far bacteria-carrying droplets expelled by sneezes or coughs travel such distances and remain able to infect other people after such a long time." explained the head of the research team, Lidia Morawska.

The team found that larger droplets took longer to evaporate and longer to deteriorate in the air. The researchers also found that different droplets coming form different parts of the respiratory system carried different loads of bacteria.

"Most of the research done in this area has been focused on laboratory-generated aerosols, or airborne droplets, which are different from natural respiratory droplets generated by humans in composition and mechanisms of production," said Morawska.

The team wanted to demonstrate how long bacteria coming from an actual human could infect another human in a closed space.  

"To demonstrate the technique, airborne cough droplets were sampled from two patients with cystic fibrosis and chronic Pseudomonas aeruginosa infection," said Morawska.

Pseudomonas aeruginosa is a multi-drug resistant germ associated with hospital-acquired infections.

The team found that the cough droplets from each of the two patients decayed in two different time spans. As soon as cough droplets hit the air, they rapidly dry out and are light enough to float around and cause infection.

"We found that the concentration of active bacteria in the dried droplets showed rapid decay with a 10-second half-life for most of the bacteria but a subset of bacteria had a half-life of more than 10 minutes," she said. "This suggests some of the Pseudomonas aeruginosa bacteria are resistant to rapid biological decay and thus remain viable in room air long enough to form an airborne infection risk, especially to people with respiratory problems such as patients with cystic fibrosis."

In other studies using the flu virus, it was found that the flu could live on hard surfaces for up to 24 hours and on tissues for up to 15 minutes. Flu viruses can also survive in droplets of air for up to 15 minutes. 

Other sicknesses like the common cold have a shorter life span. Although cold viruses have been shown to survive on surfaces for several days, their ability to cause an infection reduces rapidly, and they do not often survive longer than 24 hours. 

Experts agree that coughing or sneezing into a tissue and keeping that tissue to yourself is the best way to prevent the spread of most diseases. Coughing or sneezing into the air puts everyone around you at risk of catching whatever you are putting out into the air.