Dear Cecil: I read somewhere years ago that when you flush the toilet with the lid open, a plume of contaminated water droplets is ejected into the air and lands on everything in the bathroom, including (yuck) your toothbrush. Women I mention this to nod knowingly, but among men it is met with scorn, the common view being that this is another female scare story intended to "get us to put the top down." Knowing your ability to rise above petty considerations of gender, I turn to you. Katie Wolf, Toledo, Ohio

Cecil replies:

Opinions on this topic do seem to break down along male-female lines. “Toilet water on your toothbrush!” my assistant Jane howled. “That’s gross! That’s disgusting!” “Yeah,” said Little Ed, “it’s got Straight Dope written all over it.”

You remembered right about toilet plume, although I think toilet “aerosol” is probably the more accurate term. No doubt you saw something about Charles Gerba, a professor at the University of Arizona who specializes in environmental microbiology. For those of you with a romanticized picture of the academic life, I should tell you this means he spends a lot of time crawling around public toilets and has had the cops called on him twice.

In 1975 Professor Gerba published a scientific article describing the little-known phenomenon of bacterial and viral aerosols due to toilet flushing. The more you learn about it, the scarier it sounds. According to Gerba, close-up photos of the germy ejecta look like “Baghdad at night during a U.S. air attack.” The article ominously depicts a “floor plan of experimental bathroom with location of gauze pads for viral fallout experiments.” A lot of virus fell on those gauze pads, Gerba found, and a lot of bacteria too. In fact, significant quantities of microbes floated around the bathroom for at least two hours after each flush.

As Professor Gerba’s research would later determine, however, the bathroom was hardly the most dangerous part of the house, microbe-wise. The real pesthole: the kitchen sponge or dishcloth, where fecal coliform bacteria from raw meat and such could fester in a damp, nurturing (for a germ) environment. Next came the kitchen sink, the bathroom sink, and the kitchen faucet handle. The toilet seat was the least contaminated of 15 household locales studied. “If an alien came from space and studied the bacterial counts,” the professor says, “he probably would conclude he should wash his hands in your toilet and crap in your sink.”

Talk with this guy for a few minutes and you realize that everything people think they know about household cleanliness is wrong. You think a guy’s apartment is bound to be germier than a woman’s? Uh-uh. Single men tended to have lower bacteria counts, since they never cleaned and thus didn’t spread the crud around. (Remember this, lads, it may be useful ammunition someday.) Women’s public restrooms contained twice as much fecal bacteria as men’s, probably because the women were accompanied by sanitary napkins, grimy small children, and babies in need of a change.

Another thing. You think maybe the laundry room is germ free? Feh. The place is a sty due to fecal matter on underwear. Despite what some believe, however, doorknobs and handles in public restrooms are relatively clean.

Perhaps you think this talk of contamination is just paranoid squeamishness. You wish. Fifty to eighty percent of all food-borne illnesses originate in the home. Food-borne pathogens cause 6.5 million cases of gastroenteritis and 9,000 deaths per year. Home contamination is blamed for 20 percent of food-poisoning cases, more than any other source.

What to do? Most guys will happily go on wallowing in filth, but Professor Gerba offers these tips for everybody else: Wipe down sinks and drains each day with a cleanser containing chlorine bleach. This will knock out 99.9 percent of fecal organisms. Countertops, appliances, and faucet handles should get the treatment two or three times a week, and toilets, tubs, and showers once a week. Use separate cutting boards for meat and vegetables, lest you transfer germs from one to the other. Throw cutting boards, kitchen sponges, and dishcloths in the dishwasher (or, in the case of the latter items, the washing machine) after use. Alternatively, soak them for five minutes in a sink full of water containing a cup of bleach. When doing laundry, make underwear the last load. Don’t sort by colors (or at least don’t put colored underwear with other colored items). Use chlorine bleach, which will clean both the clothes and your washing machine. Use bleach tablets in your toilet bowl. And take it from me, if you do nothing else, put your toothbrush back in the medicine cabinet after use.

Cecil Adams

Send questions to Cecil via cecil@straightdope.com.