Many of us have learned that bacteria and viruses need warm, moist conditions in order to live, and that the human body is a perfect host for these microbes. The corollary to this is that bacteria and viruses can't survive for long periods outside the body. It turns out that this isn't always the case. In fact, the length of time that a bacterial species or virus strain survives depends on the specific microbe in question and other factors such as temperature, humidity, and even the type of surface the microbe is on.
Viruses, as a general rule, survive best on hard surfaces. Their lifespan outside of the body varies dramatically, however. For example, the smallpox virus is extremely hardy and is thought to live many years at room temperature. In fact, smallpox scabs were sometimes used in a crude vaccination method many years ago - uninfected individuals would be exposed to the scabs and eventually acquire immunity from the disease.
Other viruses can't live that long outside of the body. The hepatitis B virus survives up to 1 week outside the body, whereas hepatitis C lives between 16 hours and 4 days. The HIV virus is at the other end of the spectrum - most experts classify it as a fragile virus that quickly dies when it is outside of the body.
Bacteria appear to live best outside the body on porous surfaces. Bacteria like Salmonella and Camplyobacter, which are found in contaminated food, typically live for 1 - 4 hours. Staphylococcus aureus, the bacteria which cause MRSA infections, can live for weeks. Some bacteria are able to survive in extreme temperature and pH conditions, and others are able to form spores which allow for long survival periods in very harsh conditions.
A new study by the University of Buffalo found that Streptococcus pneumoniae and Streptococcus pyogenes appear to live much longer than was previously thought. These bacteria cause ear infections and strep throat, respectively. Anders Hakkansan and his team sampled stuffed toys, cribs, and other surfaces in a day care center and found that S. pneumoniae and S. pyogenes both survived overnight at the center - and in some cases after the surfaces were cleaned. This is something to consider in a corporate industrial hygiene program. This especially true in hospitals and food service industries.
This study highlights some of the limitations of past experiments. For instance, bacteria which are used in laboratory experiments are often cultured in the lab on standardized media. Unfortunately these bacteria may behave differently than their naturally-occurring counterparts and may yield different results. The University of Buffalo study also highlights the role that biofilms play in the pathogenesis of S. pneumoniae and S. pyogenes. These bacteria have been shown to form biofilms when they establish themselves in human tissue, so future experiments should be designed with this phenomenon in mind.
Let's put this information into perspective before we all become germophobic. It's important to remember that bacteria are all around us, and only a small percentage of them are harmful. We actually have more bacteria cells in our bodies than human cells! Viruses are also ubiquitous. They can infect every form of life, including bacteria and fungi. While viruses almost always have negative connotations, their ability to insert genes into cells hold promise for fields such as gene therapy.
The best way to avoid harmful bacteria and viruses and the diseases they transmit is to wash your hands before you eat, touch any part of your face, and insert or remove contact lenses. Wash after you use the toilet, change a diaper, blow your nose, sneeze or cough into your hand, and handle garbage or other dirty items. Wash your hands before and after you prepare food and tend to sick or injured individuals. And finally, remember to get a flu shot!
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