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Cold and flu viruses travel a tricky route

Avoiding colds and flu is hit-and-miss, and transmission isn't as clear-cut as it seems. But the classic preventive measures still seem to be the best.

January 12, 2009|Jill U. Adams

Get that flu vaccine if you want, but don't count on it to keep you healthy this winter. Sure, it can immunize you against scientists' best guess at this year's bug, but it's no guarantee you won't be confined to bed for a couple of days in the event of an outbreak. And of course, there's no vaccine for colds.

Even isolating yourself -- from family, friends, coworkers, acquaintances and strangers -- might not be enough to protect you from illness.

Scientists now know, based on recent studies, how long cold viruses can survive on telephones and money and how much flu virus emanates from a sick person's breath. What they don't agree on is exactly how colds or flu pass from one person to the next. In addition, cold and flu viruses are different enough that you can't generalize about prevention. This state of cold and flu knowledge makes science-based recommendations for staying healthy difficult.

Dr. Martin Weiss, a physician at the VA hospital in Sepulveda, says that influenza doesn't even follow any known biological model. "It pops up out of nowhere all of a sudden," he says. "Even 100 years ago when there wasn't so much travel, it would show up spontaneously in several different places."

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Touch, air pathways

Rhinovirus, the most frequent cause of the common cold, is shed mainly through a sick person's nose. In the 1960s, not long after the virus was discovered, scientists demonstrated that the virus could infect after being placed in the noses and eyes of experimental subjects, but not their mouths. So a likely infection scenario is: Joe with a cold blows his nose, gets some viral-laden mucous on his fingers and transfers the virus to a doorknob while opening a door. A while later, Bill opens the same door then rubs his eyes, giving the virus entry to his respiratory passages.

Drinking from a cup after Joe or sharing a utensil would likely pose a problem only if Joe left mucous on the cup, Bill touched the cup, and so on.

A 2007 study published in the Journal of Medical Virology showed that sick people leave cold viruses on the things they touch, such as door handles, pens and light switches. In a second phase of the study, those same subjects (now immune to that cold virus) were told to use the light switches and the telephone, upon which researchers had swabbed rhinovirus either an hour earlier or 18 hours earlier. Virus was found on their fingers after two-thirds of contacts with the one-hour-old virus and after a third of contacts with the 18-hour-old virus.

The mere presence of a virus doesn't necessarily mean it is still infectious. But a Swiss study published in Applied and Environmental Microbiology in May showed that influenza virus not only can remain on paper money for up to 17 days, but also that it can be alive and ready to infect.

Washing your hands will remove the virus from your fingertips, and an alcohol-based wipe will kill it on the refrigerator door handle. But washing hands after every instance of contact is difficult and, too often, a newly contaminated hand will wander to an uninfected eye or nose.

The likelihood of transmission via air is fuzzier. Many scientists believe that viruses may float in the air on tiny droplets or dust and be inhaled, thus bringing the germs into contact with the mucous membranes or lungs.

In 2004, a study conducted in a trio of Boston offices found viral material from cold viruses on the buildings' air filters. Further, the virus type matched that in some of the office workers. Ventilating fresh air reduced the amount of suspended virus compared with recirculated air. This suggests that sick workers were indeed expelling virus into the air. The study, conducted by Dr. Donald Milton, a professor in the School of Health and Environment at the University of Massachusetts in Lowell, was published in the American Journal of Respiratory and Critical Care Medicine.

In a more recent study published in PLoS ONE in July, Milton showed that patients with confirmed influenza released some virus simply by exhaling.

As for the likelihood of transmission via cold viruses floating around your office, researchers have shown that breathing in aerosolized cold viruses through a mask can make people sick. But that's as much as they know for sure. The best evidence would be showing real-world transmission at a distance, Milton says.

Thomas Weber, a scientist at the European Commission's Joint Research Center in Ispra, Italy, which provides scientific information to policy makers, finds it "very hard" to dismiss airborne transmission. He agrees that there's not enough evidence, but says, "To make any statements about the importance or unimportance of any pathway is premature."

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Dodging illness

Other studies have focused on prevention methods.

Research has shown that alcohol-based hand sanitizers can reduce the viability of cold and flu viruses on your hands, but washing your hands in a sink physically removes them. The effectiveness of face masks is less clear.

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