Hers isn't the fear of the paranoid. Last summer, Gallagher was hospitalized for five days and in fear for her life after falling victim to one such microbe.
The bacterium that got her was Escherichia coli O157:H7, a deadly strain of a common microbe found in people, cattle and other animals. Identified in 1982, it is one example of newly recognized pathogens showing up in unexpected places and causing concern among public health experts.
Recent outbreaks of illness caused by raspberries from Guatemala, frozen strawberries from Mexico and apple cider from California highlight how widespread the effects on public health can be in a globally interdependent world.
Even the most well-maintained market sells meat, fruits and produce that can make people sick, especially if those foods are handled carelessly. To Gallagher, navigating the well-scrubbed display cases seems like traversing a minefield. Though some risks are beyond her control, she knows that what she chooses and how she handles it can affect her chances of getting sick.
As Gallagher arrived at a farmers' market near her home in Elizabethtown, Pa., on a recent Saturday, she had one thing on her mind far more important than her grocery list: not becoming a victim again.
Food-borne diseases cause 6.5 million to 33 million illnesses a year in the United States, and as many as 9,000 deaths, according to the federal Centers for Disease Control and Prevention (CDC). Some researchers put the toll as high as 81 million illnesses - enough to strike more than one in four Americans each year.
The estimates vary so widely because only a tiny percentage of cases are reported to public health officials. Food-related illnesses, sometimes occurring days or weeks after contaminated food is eaten, are dismissed as ``a 24-hour bug'' or the misnamed ``stomach flu'' without food ever being suspected.
Scientists, who caution that people shouldn't overreact, disagree on whether the risks from contaminated food are increasing or just drawing more attention.
Disease-causing microbes, some discovered only in the last few years, are turning up in foods long considered safe and healthful: eggs, lettuce, even alfalfa sprouts.
And with the nation's growing reliance on food imports, there is concern about produce from countries with lax food inspection standards. The U.S. Food and Drug Administration says imports account for 38 percent of the fruit and 12 percent of the vegetables sold in the United States.
There is fear that Americans are getting a home-delivered version of traveler's diarrhea or worse, without the joy of traveling.
FDA scientists say that up to 2 percent of fresh produce, foreign and domestic, is contaminated with disease-causing organisms, said Lou Carson, who is managing the agency's food safety initiative.
This month, the General Accounting Office, Congress' investigatory agency, joined the Clinton administration in urging tighter controls on imported food. Both want new rules allowing the FDA to bar produce and processed-food imports from countries that don't meet U.S. health and safety standards - a rule that already applies to meat imports.
Some experts caution that there is inadequate evidence to label imported produce more risky than its domestic counterparts. In recent years, major disease outbreaks have been traced to fruits and vegetables grown in this country as well as produce grown abroad.
Rosemary Gallagher walked in to the market, with its mountains of produce, tidy counters and displays that emphasize fresh foods. Moving quickly down the aisles, she passed up freshly squeezed juices because they aren't pasteurized and refused a cut-up sample at the baker's counter.
``You don't know where the knife was. You don't know where his fingers were,'' she said.
Where the beef counter loomed to the right, Gallagher made a sharp left. She knows beef is safe if properly cooked, but she can't bring herself to eat it anymore - not after the sickness she blames on a fast-food hamburger.
The microbe that got her is rare but virulent. This was the E. coli that became known as the ``hamburger disease'' after an outbreak in December 1992 sickened 732 people and killed four children who ate undercooked hamburgers sold by the Jack-in-the-Box fast-food chain.
Since then, the bug that scientists often refer to simply as ``O157'' has been blamed in at least 29 disease outbreaks linked to ground beef, and in outbreaks linked to lettuce, alfalfa sprouts and apple cider, according to the Center for Science in the Public Interest. The CDC says it causes 10,000 to 20,000 illnesses and about 250 deaths a year.
E. coli, like other common food-borne pathogens, thrives in the intestines of healthy animals. The O157 strain is found in cattle but not in pork or poultry. Though it doesn't make the animals sick, the microbe poses a danger to people when it spatters onto meat during the slaughtering process.
Even cooked rare, most beef poses no risk from O157 because the microbe is on the surface and is killed by cooking. But when beef is ground up, surface areas are mixed in with the interior. The center of a burger that is not thoroughly cooked may contain microbes that are still alive and infectious.
Under pressure to reassure the public that hamburgers are safe, the U.S. Agriculture Department set an unusual ``zero-tolerance'' standard for E. coli O157:H7 in ground beef - a standard that last month led to the recall of 280,000 pounds of ground beef produced at a plant in Joslin, Ill., and that in August led to the recall of 25 million pounds of ground beef by Hudson Foods Co.
Enforcing the standard has also confirmed the organism's rarity. Since 1994, Agriculture Department inspectors have tested more than 20,000 ground beef samples for O157; only 13 tested positive.
Those numbers are not necessarily grounds for comfort, warned Boston infectious-diseases specialist David Acheson. Last year, Acheson found evidence that one of the genes that makes O157 so virulent - a gene that makes a poison called Shiga toxin and that can produce a severe diarrheal illness and sometimes lead to kidney failure - had spread to other strains of E. coli that appear in the U.S. food supply.
Though his studies were small, Acheson said his findings were reason for concern. His advice is to treat all meat as if it was contaminated and to cook it thoroughly.
Gallagher passed by the beef and freshly squeezed juices but then stopped at one of the potentially most dangerous places in the market - the poultry counter. She wanted chicken and turkey, foods far more likely to be contaminated with disease-causing microbes than practically anything else.
A recent study published in Consumer Reports found campylobacter in 63 percent of the chicken samples it tested, and salmonella in 16 percent. And Agriculture Department testing in 1995 at the nation's largest poultry plants showed even higher numbers: 88 percent of broiler chickens, for instance, tested positive for campylobacter.
In many large production facilities, chickens are ``basically swimming in a sea of their own excrement. It's just unbelievable,'' said Bennett Lorber, the chief of infectious diseases at the Temple University Health Sciences Center.
But mass production doesn't bear all the blame. Consumer Reports found high levels of contamination in some of the most expensive ``free-range'' chickens that it tested.
The CDC estimates that campylobacter causes 500 deaths and two million cases a year of disease - most of them minor, if two to 10 days of cramping, fever and diarrhea is considered minor. Salmonella is blamed for one million to two million illnesses and about 500 to 1,000 deaths.
Because poultry is usually served thoroughly cooked, the greatest risk comes from handling it carelessly and contaminating other foods that are then eaten raw.
Though Gallagher bought the turkey and chicken without hesitation, she had no interest in eggs sold at the same counter. She rarely buys them anymore, she said, for fear of a variety of salmonella known as S. enteritidis that lives in chickens.
Once considered essentially sterile, eggs have now joined meat in the category of ``hazardous when raw or undercooked.''
What changed? The bacterium did - by evolving the ability to infect an ovum before an eggshell forms around it.
Believing that egg-related infections came from contaminated eggshells, it took scientists years to recognize the evolutionary change. When they finally confirmed in the late 1980s that even an unbroken egg could contain pathogenic microbes, they upset centuries of common wisdom.
Foods long counted as safe and wholesome were suddenly labeled risky: homemade Caesar salad dressing, mayonnaise, ice cream and eggnog - even raw cookie dough and cooked eggs if served soft-boiled, soft-scrambled or sunny-side up.
But, as with all food-borne pathogens, the chance of an unwelcome encounter at any given meal is slight.
``We're talking about maybe one egg in 10,000 being infected,'' said Richard C. Whiting, an FDA scientist.
That's still a lot of infected eggs - roughly four million a year. The CDC says Salmonella enteritidis accounts for 250,000 to 500,000 illnesses a year.
Whiting said the biggest risk comes from small stores and farmers' markets that leave eggs unrefrigerated for hours or days at a time - a recipe for turning a few bacteria into a number large enough to cause illness.
Like other animal products, he said, eggs should not be left at room temperature for more than two hours.
It is when Gallagher starts filling her basket with fresh produce that she runs headlong into one of the great paradoxes of food-buying in the 1990s.
Fruits and vegetables, along with whole grains, are touted by virtually every expert as the cornerstone of a healthful diet. But the more healthful diet nutritionally may not be the safest as far as microbes are concerned, because produce may be contaminated and is often eaten raw.
Salmonella has shown up on cantaloupe, tomatoes and alfalfa sprouts. Hepatitis A has been found on strawberries. E. coli O157:H7 has shown up on various kinds of lettuce and alfalfa sprouts, and in unpasteurized apple cider pressed from fresh apples.
In most cases, no one is exactly sure how pathogens ended up in the food.
Improperly composted manure is one suspected source. Other possibilities are sewage-tainted irrigation water; droppings from animals, birds or insects; and contaminated wash water used to prepare fruits or vegetables for shipping or juice production.
The FDA's Carson said spot-testing produce is nearly useless for finding microbes because they appear so unevenly. Insisting on higher sanitation standards abroad won't solve all problems, either.
In the spring of 1996, raspberries imported from Guatemala sickened at least 1,465 people in the United States and Canada. The outbreak was attributed to an organism never before linked to food-borne illness: Cyclospora cayetanensis.
Hoping to avoid a repeat outbreak the next spring, U.S. food-safety officials inspected Guatemalan raspberry farms and barred imports from those that didn't meet U.S. standards.
Those measures didn't work. Another large outbreak of the diarrheal disease caused by cyclospora was linked to Guatemalan raspberries last year.
Carson said FDA scientists ``just can't figure out how cyclospora is getting on the product.'' This year, the agency threw up its hands and simply barred imports of Guatemala's spring raspberry crop.
Importation of food from around the world is only one of the new hazards. Another threat is a group of ``emerging pathogens'' - bacteria, viruses and parasites unknown a decade or two ago that produce some of the most severe foodborne illnesses.
These bugs offset some of the dramatic progress made early in the 20th century, when pasteurization and improvements in sanitation helped virtually eliminate such scourges as typhoid fever and cholera in the United States.
Scientists don't know for certain why organisms like E. coli are evolving more virulent strains or why strains of staphylococcus and salmonella are developing increased resistance to antibiotics.
One factor apparently is the widespread use of antibiotics in animal feed, which the organisms begin to adapt to. Scientists also worry about the increasing use of antimicrobial chemicals, on their own and impregnated into a wide range of products, such as cutting boards and toys.
Nobel laureate Joshua Lederberg likens the relationship between humans and microbes to a race between predator and prey, with the odds stacked against the humans. Microorganisms multiply so quickly and in such vast numbers that their evolution is extremely rapid by human standards, enabling them to counter efforts at control.
The hazards are made worse by the industrial scale of modern food production and distribution, said Robert V. Tauxe, a foodborne-disease expert at the CDC.
``When things go wrong, there's an opportunity for a lot of people to become sick at once, so we can get very dramatic, large-scale outbreaks,'' Tauxe said. ``It also means that when things go just a little bit wrong, a few people can become ill scattered over a wide area, and that's very hard to detect as an event.''
Gallagher left the market with bags of groceries that she knows pose some hazards. Her goal is to eliminate the risks she can and minimize the rest.
To protect her purchases during the ride home, and in case she needs to stop en route, she puts all perishables into a small cooler that she keeps in the trunk of her car. When she gets home, they go immediately into the refrigerator or freezer.
Fruits with washable skins - apples, oranges, even melons - she washes with dish detergent and warm water. She rinses fragile fruits, like strawberries and raspberries.
She handles chicken on the assumption that it is contaminated, thoroughly washing her hands and anything else it touches.
No kitchen precautions can prevent all risks. After the Guatemalan-raspberry outbreaks, for instance, epidemiologists concluded that washing the fruit hadn't prevented illness from the cyclospora parasite.
Many people are aware of the dangers and how to avoid them, but don't bother.
Studies show that as many as one in four consumers don't wash cutting boards after using them for raw meat or poultry. One in three say they still prefer pink hamburgers. And raw shellfish retains its cachet, even in regions where contamination has prompted warnings to avoid it.
In February, the journal Food Technology published results of a study in which researchers visited 106 homes to evaluate meal preparation behaviors. In 105 of them, ``critical violations'' of food-safety standards were identified - mistakes serious enough to spread food-borne illness.
Sara B. Fein, an FDA researcher, said of consumers surveyed: ``Close to 90 percent knew everything we asked them. They knew, they just didn't do it. They don't think it really matters that much.''
Even as they work to understand food-borne disease and lessen its impact, scientists stressed that most food is safe.
Food-safety experts say it's unrealistic to expect fresh farm products to be free of pathogens - the standard for canned goods and other highly processed foods.
Arthur J. Miller, an FDA food scientist, said consumers ``need to be very aware of the potential hazards on all raw foods. Whether it's meat or poultry, eggs, fruits or vegetables, these are agricultural commodities that come out of the barnyard, come out of the fields. And they are not sterile, so they need to be treated with care.''
Lorber, of Temple, said consumers should focus on basic precautions.
``The reality is that there are some things that can be done that are simple to do, that are routine, that can reduce risk,'' he said. But nothing can eliminate it.
In that sense, he said, food is no different from anything else for which people routinely weigh risks against benefits. Sushi, for example, carries some risks, but people love the raw fish cuisine, anyway.
``You pick your pleasures,'' he said, ``and you have a small chance of getting sick. The reality is we all eat everyday bacteria that are potentially capable of making us ill, and only rarely do we get sick.''