If you feel guilty the next time you pick up the phone to take a sick day, you may be slightly comforted to know that your job might have been the source of your illness.
Whether you work in an office or in a setting where the unclean things around you are more visible, you're likely to encounter plenty of microbes in your workplace.
"One of the reasons things get so dirty and germy is that hygiene hasn't really developed this century for workers," said Charles Gerba, a microbiologist at the University of Arizona, whose work on microbes has earned him the nickname "Dr. Germ."
But while Gerba and other researchers have studied surfaces, it seems no one has ever looked at germs across all occupations.
However, he said, the move from outdoor work to offices in the 20th century not only brought us closer together, it has allowed us to share our germs even more.
"I just think that we need to develop some kind of hygiene strategy for offices," said Gerba. "The more space we share, the more germs we share in offices.
"The office environment has created a mechanism for moving germs around," he added. "You want to make sure your immune system's getting good exercise, people always say, to go work."
But avoiding the office altogether isn't going to be an improvement. Gerba has found in his studies that home offices are even germier than ones at work.
"If you don't want to be exposed to germs, don't work at home," he said.
But exposure to all of those germs may not be a bad thing.
"If you're in a totally sterile environment, your immune system doesn't get primed for where you really need it to," said Dr. Ted Palen, an internist at the University of Colorado and a researcher in the informatics department of the Colorado Permanente Medical Group.
So, being around those germs can help protect you. And while it may also be difficult to find the least germy job, Gerba has one suggestion for those who really want to escape the microbes.
"If you want to stay healthy, become the weather center guy on the North Pole," he said.
With that in mind, we give you 10 jobs where germs can be a daily concern.
When Gerba and other University of Arizona researchers studied the desks, computers and phones from various professions, teachers wrecked the curve.
Teachers had six times more germs in their workspace than accountants, the second-place finisher, with slightly cleaner desks but five-and-a-half times more germs on their phones, nearly twice as many germs on their computer mice and nearly 27 times more germs on their computer keyboards than the other professions studied.
The reason for all the germs is, of course, the reason why the teachers are there in the first place.
"Kids' desktops are really bad, too," Gerba said. "Probably the dirtiest object in a classroom is a kid's desktop."
Children hand in tests and homework papers to their teachers, and during flu season, they often hand in cold and flu germs, as well.
Of course, the germ risk teachers face may be greater because they don't walk into their classrooms wearing hazard suits.
"In all those other jobs, I think there is more of an understanding that this is a germy job, so, hopefully, people take good precautions to keep themselves safe," said Elizabeth Scott, co-director and founder of the Simmons Center for Hygiene and Health in Home and Community Settings at Simmons College in Boston.
Judith Torian, a third-grade teacher in Needham, Mass., who once contracted bronchitis from a student, tries to avoid infections by keeping her students vigilant, as well.
In addition to her own healthy food regimen, she encourages her children to eat well every day, and teaches them cough-and-sneeze etiquette, such as coughing into their elbow to avoid spreading germs.
"In general, they're all trying not to get sick," Torian said. "We all discuss it as a group. We're all aware and really try to compliment people [for practicing good hygiene]."
Of course, being around children also presents germ concerns for day care workers.
Gerba said he often tells people, "If you don't want to stay healthy, become a day care center worker."
Because of the children, whose hygiene habits often lead to their carrying germs, microbes are abundant in day care centers, studies find.
"Certainly, [day care center workers] get a high level of exposure," said Gerba. "During the flu season ... in a day care center, about half of the objects have a flu virus on it."
The key to avoiding those germ problems, as pediatrician and day care center owner Dr. Laura Jana explained to ABC News in September, is making sure that the cleaning is worked into the daily routines.
Teachers can get sick from the germy papers their students hand in to them. For bank tellers and cashiers, much of their jobs involve handling dirty pieces of currency from all types of customers.
Almost everyone is aware of how dirty money can be, and the things you can find on its surface range from microbes to traces of illegal narcotics.
The work habits of bankers can also be a problem, as they spend a great deal of time at their desks.
Papers carrying germs come in and out, and while the papers leave the desk's surface, the germs don't.
"We found that nobody really cleans or disinfects a desk until they start sticking to it," said Gerba.
In his 2006 survey of germs in the workplace, bankers and accountants tended to be right behind teachers when it came to workplace germs, and the desks could be even dirtier.
Of course, workers who are at their desks a lot tend to eat there as well, which can increase bacteria -- and in this regard, women seem to be a little more culpable than men for the amount of food they have there.
"If there's ever a famine, I'm going to go right to a woman's desk," said Gerba.
Every so often, a study comes out declaring that your keyboard is germier than your toilet seat.
So, office workers shouldn't be offended if the computer repair person brings his or her keyboard and mouse instead of using yours.
Of course, the primary reason that a keyboard has so much more bacteria on it than a toilet seat has more to do with how frequently it is cleaned than the germs it is exposed to.
As Gerba explained, janitors often don't clean individual desks because they are considered a private space.
Of course, if you're the only one using your keyboard, that isn't a concern.
"If you're really sort of an island onto yourself ... then there's nobody to give you the flu and your risk is really low," said Dr. David Weber, medical director of hospital epidemiology and occupational health at the University of North Carolina, and a member of the American Medical Association Preventive Medicine Task Force.
But computer repair people aren't on their own.
"I have a bag I bring with me, and I'll clean anything I touch, just for sanitary reasons," said Jeremy Gauthier, owner of Metro PC Care in West Palm Beach, Fla. "I'll do the same thing in the office, when I'm at work."
Gauthier, who cleans personal computers in addition to repairing them, said that many don't believe how dirty their computer can be.
"It's really hard to convince people your keyboard is that dirty that you need a cleaning service," he said.
While Gauthier said people can clean their desks on their own, he said many will ignore it, and that the service is more about ensuring a cleansing schedule than any special cleaning products he uses.
It should come as no surprise that a place that serves sick people is also a source of germs.
And physicians and nurses can carry those germs around on their hands and their clothes.
"Certainly, health care workers are at high risk," said Weber, who, from his work in pediatrics, may be particularly at risk of picking up something.
In fact, the spread of germs in hospitals has become such a concern that new programs are trying to enlist patients to remind their health care providers to practice good hygiene.
"There's been kind of an educational push to patients themselves to ask the personnel ... before they come in, 'Have you washed your hands?'" said Palen.
While innovations may help hospitals get rid of germs, they also may help in spreading them. The push for electronic medical records may add to the risk of germ transfer in hospitals.
Not only do keyboards provide a growing environment for germs, they provide it for sometimes drug-resistant hospital germs that can be much nastier than the ones you would find elsewhere.
"As we move more and more towards using [information technology] systems within health care settings, it becomes much more of a problem," said Palen.
In fact, some researchers are testing clothing and paints that could be used in hospitals to kill nasty microbes.
Infectious bacteria and viruses may be something we try to avoid in our lives, but for many lab scientists, it's part of the job.
"People in pathology labs are working with infected materials all the time," said Scott. "You have to be very sure that you're working with it in a safe way so there's no possibility that you're breathing in infected particles and there's no skin contact."
Other steps that lab scientists need to take, said Scott, include keeping a clean lab environment, working with some dangerous chemicals under a hood that suctions toxic fumes away, and not eating or drinking in the lab itself.
"There's definitely a risk if people are not aware and not careful of what they're doing," she said.
While the rules of keeping a clean lab should be familiar to anyone who has taken a high school science class or above, that doesn't mean they have always been followed.
The strain of influenza believed to be the source of the 1918-19 pandemic, disappeared in the 1950s, when the next flu pandemic hit, but returned in the 1970s. One theory holds that it had been kept alive in a lab -- and managed to "escape."
"From historical evidence, we know that those people that have more direct contact, and people in the service industry, have a greater chance of getting the flu and cold," said Palen.
And while that can include people who need to greet others, it can include public safety officers we would hope meet fewer people on a day-to-day basis.
In addition to dealing with people who may not have the officer's personal health in mind, police officers often have to enter environments that don't have microbe safety in mind.
"There's been a lot of training with police officers putting on latex or non-latex gloves," said Palen.
And that extends to other public safety officers, such as firefighters and paramedics.
While public safety officers work their jobs with the safety of others in mind, they often need to watch out for hypodermic needles and other potentially problematic objects while in the line of duty.
"Now these people should be wearing surgical gloves while they deal with it," said Palen.
Farmers, agricultural workers and anyone with enough exposure to live animals can pick up diseases from them.
But animal control officers have the distinct disadvantage of having to deal with the unruly animals.
In addition to rabies, animal control officers can be exposed to other diseases, even when an animal is not present, such as when they are called in to clean up dead animals or animal waste.
But cleaning that waste is essential, as a variety of parasites can be contracted by children who are exposed to feces.
Of course, like germs in general, exposure to animals may not be all bad. Studies in Europe have shown that children who grow up on farms are less likely to develop allergies, perhaps because of the greater number of bacteria to which they are exposed.
Janitors and plumbers encounter many other people's germs -- and can sometimes be responsible for getting rid of them.
"When you talk about a plumber or a janitor, or someone who is cleaning an appliance in a bathroom ... they're at greater risk," said Palen.
Surfaces are responsible for a lot of the germs we pick up, and janitors and plumbers face no shortage of germy surfaces.
But if they work in a nursing home or a hospital, they may need to take extra precautions, as they can pick up the same kinds of germs that other health care workers are exposed to, noted Palen.
Because of that increased awareness, he said, janitors will take extra precautions now when they clean a health care facility. They are often compelled to wear disposable gloves whenever they clean a patient care area.
In some professions, workers are literally surrounded by germs at all times.
"I would say those are professions where you need to keep aspirate clothing for work," said Scott.
Few would question the germiness of a job where workers have to deal with solid waste all day. In a profession like this, the problem may be in bringing germs home with them.
"Their clothing should be laundered separately and washed at high temperature, with probably a bleach additive," said Scott.
Of course, sanitation workers have the benefit of knowing how dirty their surroundings are, unlike office workers, so they may be less likely to make hygiene errors.
"The fact that it looks clean or dirty may have no bearing on if it's contaminated with influenza," said Weber.
When you bring meat home from a supermarket, you cook it and clean any surfaces it touched to avoid salmonella and E. coli.
But what if, instead of a few steaks, you were dealing with an entire carcass amounting to hundreds of pounds of meat? Such is the situation faced by workers in meatpacking plants. And while they may get to wear protection against those microbes, it isn't always enough.
Last December, a pork processing plant in Austin, Minn., gained notoriety when 12 of its workers came down with a neurological illness that impaired their movement, in some cases leading to paralysis. Similar symptoms cropped up among Indiana meatpackers in January.
In February, the Centers for Disease Control and Prevention named the illness progressive inflammatory neuropathy. While investigators do not know the exact cause, the culprit in this case appears to have been contact with pig brain tissue, the result of a compressed air system that was used to blow brains out of the pig's heads.
While federal legislation has aimed to improve life for meatpackers over the years, it has not always kept them from getting sick from the harmful microbes they encounter on the job. And meatpackers may also suffer from the fact that when unsafe conditions are revealed, people's first concern may be with what they're eating, rather than how it was made.
When Upton Sinclair wrote his landmark book "The Jungle," which he began publishing as a serial in 1905, documenting the unsanitary conditions of meat production, the resulting uproar is partially credited with instigating the passage of the Food and Drug Act of 1906.
But Sinclair's book was intended to draw attention to the plight of the meatpackers at the plant. He remarked in 1906 that, "I aimed at the public's heart and, by accident, I hit it in the stomach."
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