Paranoid and carefree summer swimmers, take notice.
At least 17 percent of those smiling, splashing people admit to peeing in a pool, and 78 percent of people suspect their fellow swimmers are urinating in the water, according to a new study by the Water Quality and Health Council.
But that suspicious patch of warm water might not be the worst of what lurks in the pool, or the worst of possible unhygienic threats in summer fun.
Infectious disease experts, bacteriologists and parasitologists say some of what seems germy and gross is probably safe, while other summer fun has hidden dangers.
Although peeing in the pool was the most popular admonition, there are other poolside confessions that could cause more illness, according to the Water Quality and Health Council, which is sponsored by the Chlorine Chemistry Division of the American Chemistry Council.
Sixty-five percent of people reported that they skipped a shower before entering a pool, and it's unknown how many of those who bothered to shower took the step to use soap over a quick rinse.
"It's what a swimmer takes into the pool that makes others sick," said Linda Golodner, vice chairwoman of the Water Quality and Health Council. The Centers for Disease Control has found outbreaks of diarrhea, respiratory illness, ear and skin infections, all from a contaminated pool.
The worst infections come from -- you guessed it -- fecal matter. For that reason, the CDC recommends the following tips to keep your pool safe:
Don't swim when you have diarrhea.
Don't swallow pool water.
Practice good hygiene. Shower with soap before swimming and wash your hands after using the toilet or changing diapers.
Take your kids on bathroom breaks or check diapers often.
Change diapers in a bathroom or a diaper-changing area and not at poolside.
Wash your children thoroughly (especially the rear end) with soap and water before they go swimming.
Not that one should skip the tradition of a local pool. Unclean pool water accounted for 4,500 recreational water illnesses (RWIs) between 2005-2006, according to the CDC.
The trick, according to the Water Quality and Health Council, is to detect an unhealthy pool.
"First of all, use all your senses," Golodner said. That means look at the pool before entering and if it's clear down to the drain at the bottom, then it's likely clear of contaminants.
Golodner said using a sense of smell is important, too. An overbearing chlorine smell could actually be caused more from the chemical reaction of chlorine with urine than excessive amounts of chlorine itself. Once you're in the pool, Golodner recommends touching the sides. If the tiles feel slimy, that's likely algae growing there. Finally, Golodner says "never drink or swallow the water."
Outdoor grilling and barbecuing is a summertime staple but when it comes to cooking meat, precaution can be as valuable as a good spice rub.
Unfortunately for those who like their burgers rare, undercooked meat is a dangerous source of bacteria like E. coli and salmonella, which can make people sick or even kill them.
The 1993 E. coli outbreak at Jack in the Box hamburger restaurants, for example, brought the issue to national attention after hundreds of people were injured and four children died from eating mishandled meat products.
"The problem occurs when people don't cook the meat correctly, but it also occurs in the handling," said Sandra Bastin, associate professor of food and nutrition at the University of Kentucky.
To ensure that bacteria are killed during cooking, the meat's internal temperature needs to reach at least 160 degrees, according to the CDC. Depend on a thermometer, rather than color, to judge if a piece of meat is cooked properly, Bastin said.
Meticulous prep work can help avoid spreading food-borne illnesses. It is important to wash hands thoroughly before and after handling meat. Any surface in contact with raw meat should be kept separate from other foods and washed. And keeping raw meat cold until cooking time can prevent more bacteria from growing. Bastin recommended buying refrigerated or frozen meats last at the grocery store.
It may be true that "dirt don't hurt," but the parasites lurking in it may.
Whether it's the shore of a lake, the beach, a sandbox or some soil in the summertime, experts say it's worth following some hygienic rules.
Parasitologist Susan Wade said the occasional terrestrial parasite can make us sick, including the Toxocara canis and Toxocara cati -- essentially worms from cat and dog droppings.
"If they defecate and the eggs are in the sandbox, they take about a month to mature," said Wade, director of the parasitology section of the animal health diagnostic center at Cornell University in Ithaca, N.Y.
"If kids are playing in the sandbox and put their fingers in their mouths, they can get infected," Wade said. "It could be more than sandboxes, they could defecate any place kids might be playing in the dirt."
Raccoons can make summer fun in the dirt dangerous, too. According to Wade, they can spread the much more serious Baylisascaris procyonis parasite.
Luckily, the advice to stay safe is simple.
"Wash your hands after you've been playing in the dirt," said Wade, especially if it's in a place with lots of dogs or cats around.
The family cat and dog might seem safer (and cuter) to touch, but bacteriologist Craig Altier of Cornell says the frogs and toads you find outside could carry less disease.
Altier said that when it comes to bacteria, the biggest concern from local animals and pets on the ground might be salmonella, commonly carried by reptiles.
"Salmonella in reptiles is much more common in caged reptiles than in wild animals," said Altier, who is an associate professor of microbiology at the university's College of Veterinary Medicine. "I wouldn't freak out when my kids bring home toads and frogs."
For people who fear swimming in the great outdoors, a simple trick might be to look around at whose swimming near you.
"There are only a certain number of microorganisms that get transmitted from animals to humans," said Saul Tzipori, professor of microbiology-infectious disease at the Cummings School of Veterinary Medicine at Tufts University, in North Grafton, Mass.
Tzipori said E. coli might top the list in terms of serious infections, but there are others, all transferred from fecal matter in the water to our stomachs.
"If you are in a river or in a lake that's contaminated from other humans or animals, that's how you catch E. coli," he said.
E. coli may get more attention, but Tzipori said the chances are much greater of a person contracting Campylobacter because many animals can get it, and many animals can pass it to humans.
"It's the most common source of gastroenteritis in the United States," Tzipori said. "But it's not very serious, so you tend to hear less about it."
Also common are Giardia and Cryptosporidium, which sickened 400,000 people in Milwaukee in 1994.
"It [Cryptosporidium] is found in pools, and it's very resistant. It hangs around for a long time," said Tzipori, who added it would only take a few Cryptosporidium to make a person sick, in contrast to the relatively more E. coli needed to cause an infection.
Despite the prevalence of these diseases, experts say it should be safe to swim -- not drink -- in the great outdoors.
"If you were swimming in the water and you weren't ingesting the water, you should be OK," Wade said.
Summer picnics are marked by that iconic image of ants marching across a red-checkered cloth as helpless picnickers look on. Ants, flies and other insects are an accepted part of eating outdoors, particularly in the summertime, but they are not innocuous.
"The thought of a fly getting on the dog poo-poo and getting on your hamburger is not a very nice thought," Kentucky's Bastin said. But she noted that the overall health risks from insects landing on food were minimal, especially compared to leaving foods unrefrigerated for long periods of time.
The "danger zone" in which bacteria find it easy to grow, given enough food and moisture, is between 40 and 140 degrees. The longest stretch that food should be left above 40 degrees is about two hours.
And Bastin pointed out that time spent in the grocery store, driving home or to a picnic site and preparing and setting up a meal counts as part of that two-hour window.
"[These bacteria] are pretty common, so we're depending on cooking and handling food properly to keep us from getting sick," Bastin said.
While bowls of potato salad and cole slaw left out in the summer heat are sources of potential food poisoning, mayonnaise may have unfairly developed a bad rap.
Contrary to popular theory, mayonnaise alone is not a breeding ground for salmonella or E. coli. Commercially prepared mayonnaise is made with pasteurized eggs, effectively limiting the risk of salmonella. And because mayonnaise is made with lemon juice or vinegar, bacteria don't naturally find it easy to grow in such an acidic, low pH environment.
"But the minute you cut the baloney slice or the potatoes in potato salad and put the knife into the mayonnaise, it changes that pH," Bastin said. "When you combine [those foods] with mayonnaise, the pH goes up high enough so the bacteria will grow."
And often foods using mayonnaise are meant to be served cold. Leaving such foods out too long increases their temperature and encourages bacterial growth.