Food, Sex and Salmonella. David Waltner-Toews

diarrhea predominate.

      One group of bacteria, the Yersinia (related to the organism that causes human plague), has two members, Y. enterocolitica and Y. pseudotuberculosis, that are associated with food. In 1978, an intern from the Centers for Disease Control in Atlanta, Georgia, was going over records of appendectomies in Oneida County, New York. (This is the sort of sport in which an epidemiologist might engage during his or her spare time.) He found a definite peak in September 1976, and many of the sick kids came from a couple of small villages. His curiosity aroused, he dug deeper and found that in September and October of that year over two hundred children were sick with abdominal illness; thirty-six of them were hospitalized, and sixteen had appendectomies. This epidemic of apparent appendicitis was eventually traced back to chocolate milk provided in the school cafeteria. The milk was probably contaminated when the chocolate was mixed into the pasteurized milk in open vats. The ability to mimic appendicitis by infecting the tissues around the appendix is a particular trademark of this organism. People have succumbed to yersiniosis after drinking contaminated water or milk or eating a wide variety of foods, including tofu, chocolate syrup, raw pork, and—to put an old twist on an old saw—yellow snow.

      While we are talking about what foodborne diseases do in the human gut, I must add something else: THERE IS NO SUCH DISEASE AS THE STOMACH FLU.

      There. I have said it. When some viruses, with names like noroviruses and rotaviruses, invade the small intestine, they can cause diarrhea. Most of these viruses come from other peoples’ butts. They get into water and into food, and they travel on handshakes. Not a nice thought. The flu vaccine won’t protect you. Wash your hands.

      Bacteria or viruses that manage to cause disease in the intestine often have special antigens, or proteins. Like specialized claws, these enable them to cling to the cell walls. Bacteria such as Bacillus cereus, Clostridium perfringens, and various strains of toxin-producing E. coli will attach themselves to the intestinal walls. There they multiply and produce toxins (called enterotoxins) that mimic the body’s own secret code words (adenyl cyclase, for instance, will open a few doors), stimulating secretion of fluids into the intestines. Diarrhea and dehydration are the result.

      Other bacteria or toxins such as Salmonella, if ingested in large numbers, may simply wreak wanton destruction on the cells lining the intestinal villi, even without attachment. In these cases, the food cannot be absorbed. Or the bacteria may themselves slip past the guards, invade the blood circulation, and knock the whole body back with a generalized illness (septicemia).

      In some special cases, such as infant botulism, the normal, well-behaved bacterial citizens of the intestine have not yet moved in to set up shop, leaving their ecological niche wide open for opportunists. In other cases, antibiotics may be used, and like indiscriminate gut developers, they lay waste to particular ecological niches, where the pathogens can then multiply.

      Parasites such as the tapeworms Taenia saginata and Taenia solium will attach themselves to the intestinal wall and feed, resulting in a chronic intestinal upset.

      Many foodborne illnesses result from the absorption of toxins or viruses from the intestine into the blood; they do not cause disease in the gut itself but slip past the body’s many defenses into the circuitous channels of blood to attack, say the liver (hepatitis A) or the nervous system (paralytic shellfish poisoning). Others, like the parasites Toxoplasma and Trichinella, enter the bloodstream and, like imperialistic Europeans, invade all parts of your body, starting small communities in the warm and nutritious New World of your flesh. The most serious foodborne toxins attack your nervous system, resulting in symptoms ranging from tingling, numbness, and vertigo to fatal paralysis.

      In some cases, disease is caused not so much by the invader itself as by the immune response of the body. Hepatitis A doesn’t usually cause serious disease in children, for instance, many of whom pick up the virus in day-care centers; children’s immune systems are not well developed, and the viruses move in without causing major damage. The parents of kids from daycare centers are the ones at risk of getting very sick; when they get infected from their kids, their bodies attack the infected liver cells and they get jaundice.

      With food allergies, the intruder may seem small and inoffensive, but the body engages in a vitriolic and self-destructive war against it. There are a variety of ways to get food allergies. If you expose enough people to a food intensively, over a long period, then some of them will get allergies. That is in part why peanut allergies occur in cultures where people eat lots of peanuts and milk allergies where people drink lots of milk. Foods that are described as “nonallergenic” in North America, and that are eaten by people with food allergies, may be common causes of allergies in other parts of the world.

      Some food allergies may be acquired when your body is exposed to food molecules in unexpected ways. Let’s say that you suffer a bout of bacterial diarrhea after eating undercooked shrimp. During your illness, your gut may be damaged, and some rather large shrimp molecules may barge their way across the wall from the lumen of the intestine (which, remember, is technically outside your body) into the inner sanctum of your blood and tissues. Your body, seeing these large, predigested shrimp molecules as foreigners, in the same general category as bacterial proteins, develops antibodies against them. The next time you eat shrimp, your body, thinking that a pre-emptive attack is called for, attacks the shrimp molecules even before they get down the gullet. Each time you are exposed, the reaction is stronger, as if your body has been stockpiling nuclear weapons in the interim. Before you know it, you are gasping for breath or dead.

      In the early 1990s, I had a buffet meal with my family at a great local restaurant in St. Jacob’s, Ontario. For dessert, I chose a piece of custard pie. Within minutes, I was kneeling before the butt-throne and throwing up. When I told the sweet girl behind the counter that the pie was bad, she was flustered and offered me another piece. “No,” I told her. “It is really bad. It will give lots of people food poisoning. Probably Staphylococcus aureus.” She probably thought I was swearing and suggested that I wouldn’t have to pay for the pie.

      In the end, the restaurant gave me a free meal, but it was what came afterward that changed my life. The gut damage had allowed some larger molecules of egg to breach the intestinal walls and challenge my body’s immune system to a lifelong fight. I have always loved making and eating foods with eggs in them: Spanish omelettes, huevos rancheros, chocolate cakes, soft-boiled eggs with a bit of butter and salt, waffles, crepes and pancakes, banana cream pie, chocolate cream pie, cheesecakes of all sorts, paska (traditional Mennonite Easter bread) with fresh orange frosting—the list is almost endless. At first, when I got queasy after eating eggs, I didn’t think much of it. Then it was cakes.

      One time my wife, Kathy, and I came home from the market with a piece of Greek layer cake. “This cake is bad,” I said, running for the bathroom.

      “It is?” said Kathy, reaching for a second piece.

      Then I had scones at a restaurant that said they didn’t have eggs in them. I cured that by emptying my stomach into the plumbing system and making myself some chicken noodle soup. That was when I discovered that the noodles in chicken noodle soup have eggs in them. The last two times I reacted was when someone at Tim Horton’s assured me that their bread had no eggs in it and I just about died in the parking lot as my lungs filled with water, and on a trail in Bruce County, after having some homemade chocolate from a local store. From the Tim Horton’s episode, I learned that baking prepared in a donut-making factory probably has some egg in it. From the chocolate episode, I discovered that lecithin, an emulsifier used in some chocolates, may be from vegetable (usually soy) or other (sometimes egg) sources.

      I now carry an EpiPen (injectable adrenaline) and have to go through long explanations in airports to people who understand as much about foodborne diseases and allergies as the girl behind the restaurant counter did. I also carry antihistamines, which, if I use them as soon as I suspect there might be a problem, can head off the worst effects. Once, in Addis Ababa, I was worried about the ingredients of the food I had eaten, so I took some of the bright pink Benadryl pills I had in my pocket. I had a rough-and-tumble stomach all night. The next morning, I discovered that the pink pills I had swallowed were not antihistamines but a cathartic