London, (Agencies): Scientists have found that just a single sneeze from a flu sufferer can contaminate an entire room for hours.

At Virginia Tech, US, researchers have found that the microscopic infected droplets emitted in a cough or sneeze float around the air in large enough concentrations to spread disease.

It was reported that breathing in airborne specks of virus found in a typical office, hospital, plane or train could infect a person after just one hour.

Few studies have looked at the threat from the smaller droplets, which can remain airborne for hours or even days.

The researchers in the latest study, have collected samples of air from the waiting room of a healthcare clinic, three rooms in a nursery and three cross-country flights. Half the samples contained small droplets containing the flu virus.

The scientists found that a typical cubic metre of air contained an average of 16,000 particles of flu virus. Most were less than 2.5thousandths of a millimetre across, which remain suspended in the air for hours on end.

"The virus-laden aerosols are small enough that the smallest ones can remain suspended for days," she said.

"In this case, they are removed by other mechanisms such as ventilation, usually within one hour, from a building.

"An aircraft or office air-conditioning system does help remove the viruses by removing old air and bringing in fresh air."

A typical cough shoots out jets of air several feet long, along with around 3,000 droplets of saliva at speeds of up to 50mph. Sneezes typically contain as many as 40,000 droplets, some which leave the body at more than 100mph.

The new findings, published in the Journal of the Royal Society Interface, give a ring of truth to the old advice that you should never visit a doctor's waiting room unless you want to get sick, the researchers said.