WASHINGTON (Reuters):

Someone with a cold may just have left a little drop of virus on the light switch for you to pick up and infect yourself with, researchers found in a real-life look at how colds get passed around.

Adults with runny noses leave the virus on about 35 per cent of objects they touch, such as telephones, door handles and television controls, the researchers at the University of Virginia reported on Friday.

An hour after someone leaves a virus-infected droplet on a surface, it can be picked up 60 per cent of the time. And 24 hours later, 33 per cent of the little virus-laden droplets got on to a finger, the researchers told a meeting of the American Society of Microbiology.

"Some adults left a few ... and some contaminated almost all of the sites tested," said Dr. Owen Hendley, a professor of paediatrics at the University of Virginia Health System, who led the study.

Although the study was funded by the makers of a disinfectant spray, Hendley said it is far more important for people to remember to wash their hands.

Catching the virus

"In order to get infected with the rhinovirus which causes essentially half of the colds in adults and children, you have to get the virus on your fingertip and then you stick in your own nose and your own eye," Hendley said in a telephone interview.

His team wanted to study just how often this actually happens. So they put an advertisement in the Charlottesville, Virginia, newspaper seeking people with colds.

They found 15 who were infected with rhinoviruses and asked them to spend the night in hotel rooms.

The volunteers were asked to move around the room, sleep there, and get up and spend two hours in the room before checking out. The researchers then asked them to point to several places they had touched.

"Of the 150 sites that they pointed out to us, 52 had virus on them, which is 35 per cent," Hendley said.

WATCH THAT TELEPHONE

"The common sites were the light switch, the hotel pen, faucet handles, the door handle, the TV remote and the telephone," he said.

Two of the volunteers left no virus anywhere.

"Then there were three bad boys in there. We found virus on eight of the 10 sites which we sampled," Hendley said.

Other studies have shown that some people are "super-spreaders" of certain infections.

"Whether they were real snotty or they were sloppy, I don't know," he said. "We weren't in there watching them."

Then the researchers did a second phase.

"Because there is virus on a surface, that doesn't mean that you are going to be infected with it," Hendley said.

The researchers had saved mucus samples from each volunteer. Several weeks later, they put little drops of their mucus on surfaces in hotel rooms. Some they let dry for an hour, some were left for 24 hours.

"Each person was exposed to his or her own mucus," Hendley said — ensuring they would not become ill again.

"We asked them to flip on a light switch or to dial the 9 on the telephone or to hold the telephone handset," Hendley said.

Then they tested each volunteer's fingers. One-third of the time, a volunteer picked up virus from touching an object in a room where the virus had been drying for a full day.

In room where the virus had dried for an hour, the volunteers picked up virus 60 per cent of the time.

"So your husband could leave it there for you and go to work and you could by chance turn on a light and if you then put it in your nose and your eye and get infected," Hendley said.