New research details how several surfaces in a home with a family member who already has a cold are likely to become contaminated with a cold virus, including refrigerator doors, remote controls and bathroom faucets.
The report, conducted by researchers from the University of Virginia Health System, was presented today at a joint meeting of the American Society for Microbiology and the Infectious Diseases Society of America in Washington, D.C.
The researchers asked participants with a cold to identify 10 surfaces they had touched in the last 24 hours. The scientists then tested the surfaces for detectable levels of rhinoviruses -- the family of viruses that cause the common cold.
Forty-two percent of the surfaces examined tested positive, including eight out of 14 refrigerator door handles and six out of 18 doorknobs.
"The refrigerator door handle was a big boy, needless to say," said Dr. J. Owen Hendley, one of the study's authors and a professor of pediatric infectious disease at University of Virginia Children's Hospital.
Other objects that showed a higher percentage of positive test results included bathroom faucets (eight out of 10 tested) and television remote controls (five out of 10 devices tested).
"The sites that were contaminated were not particularly surprising, because it's what people touch a lot," said Hendley.
What was more interesting to Hendley, he says, was a second experiment the group did to see how easily the virus particles transferred to people's fingertips.
The experiment required participants to touch dried spots of virus-filled mucus on three pre-exposed objects -- a light switch, a phone handset and a phone keypad. The mucus came from the participants, themselves -- before they recovered from their illnesses.
"At the times that they had a cold, we said, 'Bring us in a half a teaspoon of snot,'" said Hendley, who froze the mucus until the participants were cold-free.
The scientists then had the subjects touch the objects one hour after the mucus was deposited -- also 24 hours later and 48 hours later.
Traces of the virus turned up on fingertips 89 percent of the time after the one-hour exposure period; the number dropped to 69 percent after 24 hours and 53 percent after 48 hours.
But further analysis showed the rates were lower when considering whether the virus could be classified as infectious (not just present on the fingertips). In that case, the researchers detected infectious rhinovirus on 24 percent of fingertips after an hour; the infectious transfer rate dropped to 4 percent after 24 hours and zero after 48 hours.
The infectious virus apparently decays at 24 to 48 hours, said Hendley, who noted the transfer rate of virus to fingertips could be increased if someone has a particularly high load of viruses in their mucus. But you'd be hard-pressed to know that ahead of time.
"Can you tell [their viral load] from how bad their cold is? The answer is no," he said.
One could certainly avoid making contact with such household objects entirely, but doctors recommend a more reasonable alternative.
"If you yourself have a cold or if other members in the family have a cold, they should wash their hands," said Dr. Jon Abramson, who was interviewed for ABCNews.com.
"Also, when you're coughing or sneezing, you should cover your face with either your hands or your elbow," said Abramson, chairman of the department of pediatrics at Wake Forest University Baptist Medical Center.
Hendley has similar advice: "When somebody at my house has a cold, I'm not prepared to treat the surfaces, but I sure as hell wash my hands before I stick them in my nose or eye."