Each year, 48 million Americans eat something that makes them sick to their stomach. While most escape with nothing worse than a miserable night spent in or around a bathroom, statistics from the Centers for Disease Control and Prevention show not everyone is so lucky. About 128,000 people are hospitalized and some 3,000 die each year from the over 250 different foodborne diseases caused by viruses like norovirus or bacteria like Salmonella that plague our plates.

Despite advancements in modern technology and medicine, this ancient problem endures: Trojan Horse-style invasions of tiny beasties hidden in the food that nourishes us.

Even estimating the problem's size is difficult, because most foodborne illnesses still go unreported, says Ben Chapman, a food safety specialist at NC State University. “For every case that gets reported in our health care system, meaning we've been able to pull a bug out of a stool sample and confirm it, we've got a pretty good idea that another 40 illnesses go undetected,” he explains.

Fortunately, scientists now know many of the culprits that commonly turn good food bad. Salmonella—which causes cramps, diarrhea and fever, but also kills some 450 Americans a year by spreading to the bloodstream—sickens some 1.2 million Americans a year. Listeria impacts just 1,600 people a year, but of those some 260 die: When these bacteria spread beyond the gut, they can cause confusion, loss of balance or convulsions within weeks.

Though many strains of E. coli bacteria are harmless, their pathogenic relatives can cause stomach-turning effects from diarrhea to respiratory illnesses by pneumonia. And norovirus, the most common cause of stomach and intestinal ills, infects some 20 million Americans a year. However, of that huge number, just 570 to 800 die, and most of them are young children or the elderly—two groups that are at particular risk for foodborne ills.

In 2013, the CDC commissioned a study to find out which foods make people sick the most often. Some of the culprits—shellfish, dairy, undercooked meat—might not surprise you. But others were less intuitive.

For instance, given how many warnings we tend to hear about spoiled and undercooked meats, many tend to think of animal products are the source of most foodborne illnesses (which is likely why we've evolved disgust reactions to animal products that we don't have with plants, says psychologist Paul Rozin at the University of Pennsylvania). In actuality, nearly half of all illnesses the CDC tracked from 1998 to 2008 were caused by produce, which includes fruits, nuts, roots and leafy greens. Salad lettuce and spinach caused 23 percent of illnesses, the most of any category.

That doesn’t mean animal products aren’t implicated in those outbreaks, says Sandra Eskin, food safety director at The Pew Charitable Trusts. “Many of the pathogens that we worry about in produce, like E. coli or salmonella, actually are of animal origin,” she explains. “So if you have a field of spinach contaminated it's coming from somewhere else, on neighboring farms. Maybe it's in the water that's used for irrigation, or wind brings it in from a nearby cattle operation.” In other words, even vegetarians can suffer from side effects of meat and poultry operations.

There's also growing evidence that these pathogens can survive for a long time in soil and other environments, says Chapman, citing recent ilness outbreaks stemming from almonds, peanut butter and flour that seem to have no discernible animal sources. “Increasingly we're opening up our minds and saying the environment might also be a pretty decent source for hosting foodborne pathogens," he says.

The good news about salad-induced stomach ailments is that—while certainly unpleasant—most aren't serious. Norovirus, for instance, usually just means you're in for a few days of diarrhea or vomiting. The reason produce accounts for so much sickness isn't because it's particularly risky, says John Painter, the CDC epidemiologist who authored the study. “As it turns out, many foodborne illnesses are attributed to vegetables, but one reason for that is that we eat so many of them," Painter said in a 2013 podcast explaining the results.

He added: "Keep eating your vegetables."

The same study found that meats and poultry accounted for 22 percent of all illnesses, but also featured higher percentages of serious sickness and deaths, some 29 percent. About 19 percent of all food-related deaths were caused by poultry alone, numbers particularly driven by three large listeria and salmonella infections in sliced poultry meats, the last of which happened in 2002. Dairy and eggs combined to produce 20 percent of all food illnesses while fish and shellfish accounted for just 6.1 percent, which mainly just shows more that Americans eat them less frequently.

But let's get to the meat and potatoes of the matter: If you're really trying to dodge food poisoning this holiday season, what should you avoid? Read on.

Sprouts

Yes, fear the sproutbreak. Outbreaks due to contaminated sprouts have occurred at least once a year for more than two decades, according to the CDC. “Sprouts are grown in water, and bacteria love water,” Eskin notes. Bacteria also love the nourishing environment of the sprout seed, where organisms like Salmonella, E. coli, and Listeria make themselves at home. If you do roll the dice by eating raw sprouts, you should know that the risks can impact even healthy people: just look at the sprout-based E. coli outbreak that swept across 16 European nations in 2011 and claimed 50 lives.

Raw Oysters

Oysters, like most bivalves, are filter feeders. That means they pump gallons of water in and out of their bodies, accumulating bacteria as they go. Unfortunately some of those bacteria, like Vibrio, can really lay humans low. Most Vibrio sufferers experience nausea, headaches and the chills. The distinctly nastier (but fortunately far rarer) V. vulnificus infection can progress to blood poisoning and death, particularly in those with liver problems, diabetes or weak immune systems.

“Maybe not a large number of people get sick from eating oysters, but when you do it can be pretty serious and they have a relatively high mortality rate in terms of foodborne illness,” Eskin says.

Cooking oysters generally eliminates the problem, by destroying the bacteria. But if you can't live without a shuck on the half shell, know that Vibrio multiplies in warmer water, so it helps to make sure your shellfish come from cold waters. That's why California restricts the sale of raw oysters from the Gulf of Mexico during the warm months of April to October, unless they've been treated with pasteurization-like techniques. The shellfish industry and oyster lovers fought the FDA's efforts to implement a similar ban in 1995, insisting that the product simply wasn't the same and that the small risk was worth taking.

We'll let you decide.

Raw Milk

Proponents of drinking raw milk claim it confers health benefits that help with everything from asthma to allergies; thus far such claims tend to be largely anecdotal rather than evidence-based. But Eskin reminds us of the simple reason that widespread pasteurization of milk began in the first place: “Pasteurization kills the pathogens that make people sick.”

Even healthy animals raised in sanitary conditions can carry such germs, and the data suggests that they often do. U.S. Public Health Service epidemiologist and veterinarian Casey Barton Behravesh cites some sobering statistics on the federal government site Foodsafety.gov: Though only 4 percent of dairy products consumed in the U.S. are unpasteurized, more than half of dairy-associated outbreaks are linked to raw milk products, based on a 2006-2007 FoodNet Population survey.

It’s true that it’s possible to get “food poisoning or foodborne illnesses from many foods, but raw milk is one of the riskiest of all,” writes Behravesh, who investigates outbreaks caused by contaminated food. “Getting sick from raw milk can mean many days of diarrhea, stomach cramping and vomiting. Less commonly, it can mean kidney failure, paralysis, chronic disorders, and even death.”

Ground Beef and Chicken

Bacteria like E. coli live in cattle intestines and can contaminate meat during slaughter. Ground meats spread the problem around, however, by mixing parts of many animals together. Chicken outbreaks often involve Salmonella, which is brought into the slaughterhouse by live birds. That means that, when it comes to foodborne illness, meats are in a class by themselves.

The Center for Science in the Public Interest, a nonprofit consumer advocacy group, combed through 12 years of data on 1,700 food-related outbreaks to determine which meat and poultry products carried the highest risk. Ground beef and chicken topped that list in their resulting Risky Meat report.

Problems with meat and poultry can be exacerbated by antibiotics, warns Bruce Y. Lee, an associate professor of international health at the Johns Hopkins Bloomberg School of Public Health. “We're seeing at the farm heavy use of antibiotics, and that's not going to prevent contamination or foodborne illnesses,” he says. “Also, people taking them whenever they don't feel well due to foodborne illness isn't a solution. Most studies have shown that cases of self-limited gastroenteritis are not going to really benefit from a course of antibiotics.”

In fact, Lee notes, both types of overuse may make the problem worse by encouraging strains of pathogens that are resistant to antibiotics and pose a greater threat to the safety of the food supply.

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So how concerned should we really be about foodborne illness? Chapman says that attitudes to the risks of food poisoning tend to vary with personal experience and years of consumption.

“We consume billions of meals a year that don't make us sick, and then there are millions of meals a year that do make us sick,” he says. “I think it's human nature to live anecdote to anecdote. If I've been undercooking my burger for 20 years and I've never gotten sick, I'm very comfortable with that. You can tell me about the risk, but I've never seen it realized. On the flip side, I know people who've lost loved ones to foodborne illness and they look at things drastically differently.”

But on the front lines of the battle for food safety, new weapons are helping to even the odds. Veterinarian and biomedical scientist Karin Hoelzer, also with Pew, is particularly enthusiastic about the potential for genome sequencing to enable incredible detective work. “Whole genome sequencing gives us orders of magnitude more information, so it's much easier to isolate bacteria and to be confident that they are closely related and likely come from the same source,” she says. “In the last two years a lot more outbreaks have been recognized ... Hopefully they will also be able to detect them more quickly and before more people get sick.”

Of course, while we're hard at work evolving our defenses, so are the invisible enemies that threaten our food supply. “Today's risky food can be replaced by tomorrow's risky food,” Eskin points out. She cites unprecedented listeria outbreaks, including one in Blue Bell ice cream across southwest Texas. “There was some assumption that freezing would control listeria,” she notes. “But what apparently happened was that melted ice cream was used in milkshakes and somehow that reactivated listeria.”

Hoelzer adds a similar tale of caramel apples that proved fatal for several people and puzzled experts for some time. “When the caramel was put on the apple it created a bit of space between them, and when the stick was put in some of the juice from the apple filled that space. And that was a perfect environment for listeria to grow as these apples sat on the shelf at room temperature,” she says. “Nobody thought of these things. Very smart people who've spent their careers on food safety and science had never seen this in caramel apples.”

Though those might have been firsts, Eskin adds, they won't be the last time an unexpected food causes chaos in American stomachs. “These bacteria are very smart,” she says. “And they want to keep reproducing.” To stay ahead of these adaptive little organisms, we'll have to keep evolving in response.