If your brother or sister gets a cold, there’s a good chance that you’ll pick up the same bug—either directly or from something he or she touched or sneezed on. In this Science Update, you’ll find out how long a germ can hang around and wait for its next victim.
What's the life span of a germ? I'm Bob Hirshon and this is Science Update.
When one family member gets a cold or the flu, it seems like only a matter of time before everyone in the house gets sick. That got Michael Guccione of Naperville, Illinois, to wondering how long these viruses survive on surfaces, and if that's how they get passed from one person to another.
Well, Michael, we asked Dr. Don Goldmann, an infectious disease specialist at Children's Hospital in Boston. He says cold viruses can live for up to six hours outside the human body.
And they are spread by this sort of careless touching of contaminated surfaces. Or for that matter, just directly wiping the snotty nose of a child and getting your hands contaminated.
That's why he says it's important to practice good hand hygiene—washing with soap and water, or using a sanitizing gel that contains alcohol.
The flu virus, though, spreads differently—mostly through the air when someone sneezes or coughs.
So yes, the surfaces can be important, but this is more of a droplet and airborne virus than some of those other cold viruses.
If you've got the germ of a science question, call us at 1-800-WHY-ISIT. Or e-mail us from our website, www.scienceupdate.com. If we use your question on the show, you'll get a free Science Update mug. I'm Bob Hirshon for AAAS, the Science Society.
Making Sense of the Research
How long does a cold virus last? That depends which cold virus you're talking about. The illness we call a "cold" is actually a collection of symptoms that can be triggered by a wide variety of viruses. Some common types of cold viruses include rhinoviruses (the prefix "rhino" means "nose"), respiratory syncytial viruses (commonly found in babies), and coronaviruses (a nasty strain of coronavirus causes Severe Acute Respiratory Syndrome, or SARS).
Within these and other groups, there are dozens, even hundreds, of different strains of virus, and they’re constantly mutating. As long as your immune system is working properly, you can't catch the same virus twice, but there are still plenty more to go around.
As Goldmann explains, cold viruses can live on contaminated surfaces for up to five or six hours. But just touching the surface usually isn't enough to get you sick: the skin on your hands is a pretty tough barrier for cold germs. When the cold virus does manage to infiltrate your body, it usually gets in through an entrance that isn't so well guarded, like your nose or your eyes. (Your mouth actually isn't such a great way in, as it turns out—so kissing is relatively safe.)
Now, few people actually rub their noses or eyes directly on doorknobs, used tissues, or other surfaces that can carry the cold virus. But if you touch these things and then scratch your nose or rub your eyes, you've just given the cold virus a free ride into your body. That's why hand washing is the most effective way to avoid picking up someone else's cold germs.
The flu virus can spread this way too, but unlike most cold viruses, it's also carried easily in droplets of moisture in a sneeze or a cough. Because of that, the flu spreads more easily than most colds. Luckily, most flu seasons are dominated by only a handful of different strains of the virus, making it possible to create an effective vaccine that will prevent most cases of illness.
Now try and answer these questions:
- How are cold viruses passed from one person to another? Be specific.
- How does the flu virus behave differently?
- Why is hand washing an effective defense against the cold virus?
- Would any of this change if the cold virus could live for a week outside the body? What would be different? Would certain forms of prevention become more or less important?
- Suppose only a few different kinds of viruses caused colds. How would our prevention strategy change?
CommonCold.org is a comprehensive, updated reference source for information about colds and cold viruses.
The American Lung Association publishes this page of Guidelines for the Prevention and Treatment of Influenza and the Common Cold.
Influenza 1918, an episode of PBS's The American Experience, details the most devastating epidemic in American history.