Here’s how far germs spread when you sneeze – and you’ll never guess how long they live

WE all know it's important to cover our mouth when we sneeze.

It traps germs and could stop another person from falling ill.

But do you know exactly how far your germs can travel, or how long they can live?

The grim truth is germs carried in droplets from your sneeze can travel as much as four metres.

And they can live for up to 45 minutes - long enough for several people to pick up what you have spread around.

Scientists at the University of Queensland in Australia have not only discovered how far disease carrying bacteria travelled, but also how it travels.

They looked at the lifespan of pseudomonas aeruginosa bacteria, a type of bacteria that can cause infection in people whose immune systems are already down.

It is most commonly associated with hospital-acquired infections, such as pneumonia, and is spread by coughing and sneezing.

Professor Lidia Morawska, lead author and director of the International Laboratory for Air Quality and Health at the university, said: "Our previous research had found that these pathogens travelled up to four metres and stayed viable for 45 minutes after being coughed into the air.

"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.

"Most research in this area to date has focused on laboratory-generated bio-aerosols, or airborne droplets, which are different from natural respiratory droplets generated by humans in composition and mechanisms of production.

"We developed a novel technique to target the short-term and long-term ageing of bio-aerosols from people, without contamination from the ambient air."

Professor Morawska and her team sampled cough droplets from two patients with cystic fibrosis and pseudomonas aeruginosa infection.

But the bacteria died at different rates.

The larger the droplet of bacteria the longer it took to dry out and, therefore, the longer it lived outside the body.

This poses a threat to vulnerable patients who may be exposed to the germs.

Professor Morawska added: "As soon as cough droplets hit the air they rapidly dry out, cool and become light enough to stay airborne.

"They also partly degrade through contact with oxygen in the air, with larger droplets taking much longer to evaporate.

"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.

"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."

Professor Morawska said the findings could help improve infection control within hospitals.

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