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2 THE VOICE OF THE UNSEEN GUEST

HOW PEOPLE GET SICK

WHEN ANTON van Leeuwenhoek looked down his crude microscope in 1674 and discovered a world of “very little animalcules,” he did not imagine that whole populations of these tiny creatures attended our every meal and entered our bodies unheralded. Or that there might be even smaller beasties, the viruses, inside the tiny bacteria he was seeing. Nor did those devout families who set out an extra chair for the Unseen Guest at their meals imagine that they were surrounded by millions of unseen guests who had no need of chairs.

Wading into the orgiastic world of microbes can be disconcerting. Why would any morally upright God create such an amoral mess of living things, breeding and crossbreeding, exchanging genetic material without regard for race, creed, species, or sexual preference? Right under our noses? Right in our noses? I am not a theologian, and cannot understand this, but we shall probably have to pinch our moral noses as we explore this world in order to rescue the maiden of our amazing and improbable lives.

When these microscopic bacteria and viruses enter our maws, riding on eggs and hamburgers as children in an amusement park might ride into a tunnel of ghosts, with what voices do they scream their joy and terror? How, in short, do they make us sick?

One might say that contaminants in our food can make us sick in one of two ways: through intoxication or through infection. Intoxications, caused by toxins in food, occur within minutes to hours after eating and are most often associated with vomiting. These are, technically, what we can call food poisoning. Infections, which require time for bacteria from the food to multiply inside the host’s body before they cause havoc, develop hours and even days or weeks after eating, and the main sign is diarrhea. This would be called a foodborne infection. “Foodborne disease” covers both intoxications and infections.

Vomiting and diarrhea are the two most common characteristics of foodborne disease. I refer to them as “signs,” which should be differentiated from “symptoms.” Although many other writers are less careful in their use of these words than I am, the distinction is useful. A sign is what can be seen and measured in some way, like temperature, pulse, and the amount of water in your stool. A symptom is something you feel, like pain, a headache, or tingling in your fingertips. The distinction is obviously useful for a veterinarian, but it is also important for people. A doctor can (at least theoretically) measure a sign, even if the patient is a young child; you have to tell the physician about your symptoms. Most diseases present as a mixture of signs and symptoms.

If we call diarrhea a sign, which I would, you might well ask how we can measure it. Diarrhea occurs when a person’s feces have increased water content above what we normally expect; not to put too fine a point on it, the feces flow, rather than plop. One could, of course, measure exact water content of a stool, but the simplest definition of diarrheic stool is that it takes the shape of the container into which it is put. Public health officials then usually say that a person has diarrhea if he or she has two or more (or occasionally three or more) such stools in a twenty-four-hour period.

Vomiting, also called emesis, occurs when your abdominal muscles and diaphragm contract, throwing the contents of the stomach and upper small intestine up through your esophagus and mouth (and, if you are really unlucky, your nose). Vomiting is controlled by a certain part of the brain, which is excited when it receives messages from certain nerves, many of which have endings in the stomach and upper small intestine. These nerve endings are switched on by both physical and chemical stimuli. As with diarrhea, the amount and timing of what comes out of your mouth could be measured, which is why I would call it a sign.

But there is more to this story than what comes out the orifices of one’s body, instructive as that may be. Let us contemplate, for a moment, food as it passes our lips into the masticatory caverns where lurk the uncompromising teeth and the probing tongue. At the risk of self-absorbed intellectual implosion, let us further contemplate the tiny bacteria that may dwell within that food, whether they be friendly lactobacilli in yogurt, interloping Salmonella in cheese, or the parts per billion old or new chemicals that contaminate the interstices of complex carbohydrates or comprise the food itself. In so doing, you may gain some understanding of how you can get sick from so apparently a feeble sin as eating an egg soft boiled.

Forget, for a moment, the candle, the wine, that ambiguous look across the table. This is what it comes to: food is ground up and mixed with saliva in the mouth. Saliva contains, among other things, amylase, an enzyme to aid in digesting starch. It serves, as well, as a solvent for food chemicals, thus allowing one to taste them. Taste is a first defense against foodborne disease. I am quite suspicious of so-called acquired tastes. Not all foods that can make you sick taste bad, but—certain Danish cheeses, Chinese eggs, and Scandinavian putrefied fish aside— foul tastes and odors, metallic tastes, and burning sensations should serve as a warning.

Nevertheless, I confess that I, too, once polished off a bad-tasting steamed bun from a food court for a negligent nephew. It was from a Vietnamese fast food restaurant, and I felt a certain duty not only to eat the food but also to like it, as penance for coming from a culture that had behaved so miserably toward Vietnam. If I expected God to reward my virtue in finishing a bad-tasting bun, I was wrong. I not only felt miserable during the baked salmon candlelit dinner that evening but also spent what would have been the better part of my Christmas holidays bent over a porcelain throne, wishing I were dead. This kind of behavior may have something to do with parents who make an issue of food, drawing tight and judgmental arguments around the uneaten chicken and the starving children in India, China, or Ethiopia. Guilt and food are a common and deadly combination.

Our mouths have a large and complex natural bacterial flora that rarely cause any disease, unless you bite someone. Moreover, bacterial infections may put you off your food, but they seldom attack your mouth directly. Occasionally, foodborne diseases are associated with a sore throat. Beta-hemolytic Streptococci, the cause of strep throat, have managed on at least two occasions in the last decade to use food handlers to perpetuate themselves: once through a chocolate mousse fed to people at a blood bankers’ conference in Kansas City and once through cold meatballs fed to soldiers at an Israeli military base.

Toxins—either those inherent in some foods, those added by our bacterial friends, or those that we add deliberately or inadvertently—are another matter. In very high doses they may induce irritation at the back of the pharynx, and hence retching, which is different from vomiting. Some toxins may produce burning or tingling sensations. What they do at low doses is the topic of a later chapter.

Safely past the teeth, the tongue, the tonsils, and the salivary glands, your food now takes that not-quite-irreversible plunge down the esophagus, white-water rafting on peristaltic waves down to your stomach. The image of a watery torrent is not so far off the mark. Consider for a moment the following estimated flow of fluids through your body every day: about 2 quarts of intake, 6 quarts of saliva and gastric, bile, and pancreatic juices, and 6 quarts of secretions from the intestines—for a total of 3 to 4 gallons! And these fluids are not just water; they contain all manner of essential electrolytes, such as sodium and potassium. Yet on a normal day in a normal person, less than a cup of that amount gets out the back door. Most of it is re-absorbed in the lower part of your intestines; this re-absorption is essential to maintain your body’s fluid and electrolyte balance. It does not take much imagination to consider the havoc that might be wreaked by a small hole in the dike, the work of a tampering bacterium or virus.

At the stomach, the cardiac sphincter, the front door, opens to let food in but sometimes sprays a bit of acid up into the soft flesh of the esophagus, resulting in heartburn.

The stomach accepts the now somewhat sorry-looking foods as hand-me-downs from the mouth, grinds them into smaller particles, and churns up an emulsion of the fats. Sloshing about in this very acidic fluid, the food undergoes some preliminary digestion. As one might imagine, for the bacteria stowing away in our food, this acid bath is the most potentially deadly part of the ride.

If the collective bacterial mind thinks that our mouths provide easy access to the internal offices of the human body, they are sadly mistaken. The lumen, or inside, of the gastrointestinal tract, from mouth to anus, is technically outside our bodies. While the inside of the gut has direct connections with the world around you, and is full of all sorts of bacteria and viruses, the true “inside” of your body is sterile. A heart surgeon has to wear a mask and gloves to protect you from infection; my family physician checking my prostate gland wears a glove to protect her, not me. The gut is lined with protective barriers and guardian cells. It is their job to let in only those molecules that know the appropriate code words.

A great many bacteria die in the stomach. How, one might ask, do any of them survive? Sometimes we unwittingly give them help. An antacid taken for the heartburn, for instance, helps neutralize the stomach’s acids and makes it more comfortable not just for you but for the little lives within you. Infants naturally have less acidic stomach contents and so are more likely to give the bacteria a home. Food may also protect the bacteria, which snuggle unmolested in its depths. Furthermore, some vessels give the bacteria a slower ride through the acid. Small amounts of carbohydrates may pass through the stomach in thirty minutes or less. A high-fat meal may take several hours to move on.

With the exception of organisms such as Helicobacter pylori, which causes ulcers and is probably transmitted through contaminated food and water, bacteria rarely find the stomach sufficiently hospitable to take up residence there. Toxins are a different matter. They may irritate the stomach directly or may slip off to one’s neural vomit center, where they stimulate a relaxation of the cardiac sphincter and esophagus, with simultaneous contraction of the abdominal muscles and viscera. Throwing up is an apt description; one might imagine a small but powerful baseball player hiding in one’s depths.

Toxins formed by the bacteria Staphylococcus aureus (which hang around many people’s noses) and Bacillus cereus (which prefer rice fields) may attack in this way. Metals such as copper, zinc, tin, and cadmium, if ingested in high doses, may do something similar. We might ingest such metals through leaching from a container or because our crops were grown in industrially contaminated soils.

Now that your food has survived a trip through the stomach, your gastronomic happiness rests in the hands of the small intestine, a 23-foot-long glistening, slithery tube. Although many toxins that can damage the stomach also attack this part of the gut, it is here that infectious agents such as bacteria and viruses first enter the fray. To describe this place appropriately, one must stoop to the cryptic and bilious language of darkness and melodrama. Enzymes are secreted by the pancreas and by cells in the crypts lining the long, serpentine halls. Bile from the liver enters the first part of the small intestine, the duodenum, and makes the fat soluble. Food that is broken down is ingested through the absorptive cells clustered on the folds, called villi, which, for bacteria, is the plural of villa, a great place to luxuriate.

Farther along, in the lower part of the ileum, most of the fluids and electrolytes mentioned earlier are absorbed. Few bacteria live naturally in the upper small intestine. Buffeted by peristaltic waves and rained upon with bile salts, they tend to move on in search of more hospitable environments. As well, the normal bacterial burghers of the lower small intestine fill up the available living space and effectively exclude, in most cases, all but the most aggressive newcomers. This phenomenon has been called competitive exclusion and is the rationale behind eating friendly bacteria, say, from yogurt, to prevent the pathogenic, disease-causing ones from moving into your neighborhood.

The small intestine is the central starting place for most foodborne illnesses. Nausea and vomiting, as in the stomach, still occur but are less common the farther into the bowels the intruders descend, at which point abdominal cramps and 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 (an antidote to constipation). I guessed that there had been no eggs in what I had eaten, or I would not have survived the night.

I could likely sue the restaurant owner, but he’s an acquaintance, so I haven’t even told him. Which is probably irresponsible of me. Instead, I have my students prepare public dissemination projects and hammer into them the public part of public health. And I write books like this one.

At least one kind of food intoxication mimics an allergic reaction. Sometimes, in scombroid fish such as tuna and in some cheeses, bacteria may partly digest the food (some might call it spoilage, but I am trying not to be judgmental). When eaten in large amounts, such spoiled foods cause symptoms that may be confused with those of true allergies: a burning in the mouth and throat, flushing, and dizziness.

In early March of 1981, a young, organized British Columbia woman bought two cases of canned tuna. She opened a can from the first case and ate the contents, despite their strange, bitter taste, on March 15. About half an hour later, she felt nauseated, her throat was swelling, and she felt hot; she also developed what appeared to be a rash on her chest and back. On March 22, probably thinking about fiscal responsibility and the large investment she had just made in tuna, she tried again, with the same results. Almost exactly nine years later, three people in downtown Toronto tried out a local luncheon special of mahimahi fish. Within the next hour, all three felt as if they had a sudden sunburn. Peppery taste, headache, dizziness, diarrhea, and flushing are recognized symptoms of food allergies.

At one time, scombroid fish poisoning was thought to be a kind of allergy. Now we know that it is neither an allergy nor restricted to scombroid fish such as tuna, mackerel, and other dark-fleshed fish, like mahimahi. Scombroid “fish” poisoning has also been reported from eating Swiss cheese. Some bacteria will digest foods containing the amino acid histidine, such as fish that have not been cleaned and chilled quickly enough. The product of the bacteria’s labor is histamine, the same compound made by our own bodies during an allergic reaction—hence the similarities in clinical picture. The big difference, however, is that our bodies learn from a food allergy. One encounter, however benign, enhances the seriousness of the next. Scombroid toxicity is more like a predictable aunt, with unchanged irritability from visit to visit.

In both neurological and allergic-type reactions, ordinary citizens might ascribe their state to a stimulating dinner companion, were it not followed so inconveniently by more serious gastrointestinal or neurological complications.

Foodborne illnesses may also result from food intolerances, in which case your body does not have the enzymes necessary to digest certain parts of certain foods. Milk intolerance is a common problem among some ethnic groups, which results in frothy diarrhea and cramps. Many of us can recall stories of poor villagers in some developing country using powdered milk to whitewash their houses. One might view this use as a form of ingratitude in the face of our obvious generosity, but such generosity is not much different from their sending us skewered cockroaches to solve our food problems. Another food intolerance, this one found in many people of Mediterranean origin, is called favism. These people can develop an acute hemolytic anemia if they eat fava beans.

The large intestine is mostly a place where fluids and electrolytes get sucked back into your body. Being less acidic than other parts of your gut, the large intestine is generally hospitable to bacteria, many of which normally make their home there and don’t cause illness. In fact, one might suggest that the only ecological and evolutionary justification for the human race is to serve as a living area for large numbers of anaerobic (air-intolerant) bacteria. This perception is not as heady as thinking of ourselves as the brains of evolution, but in ecologically recessionary times, when millions of species are going extinct for lack of a working niche, it is at least a job. The total number of bacteria excreted by an adult each day ranges from a hundred billion to a hundred trillion.

If pathogenic agents do manage to get a foothold in these nether regions, we feel lower abdominal cramps and can develop bloody diarrhea. Red blood in the feces is a sign that the destruction must be quite low down, because blood entering the intestines higher up turns black through partial digestion.

Finally, high-fiber foods such as bran will draw water into the large intestine and smuggle it away to the great outdoors in what is called an osmotic diarrhea.

The foregoing are the acute effects of foodborne diseases. These diseases may also have long-term effects, sometimes called sequelae. Reactive arthritis develops in more than 6 percent of people who get salmonellosis and in probably 1 percent of those with Campylobacter infection. Campylobacter infections can be followed by Guillain-Barré syndrome, in which people develop burning sensations and paralysis; 15 percent of them die. There is also some evidence that foodborne infections may contribute to plaques in blood vessels and hence to cardiovascular disease. Diseases caused by E. coli O157:H7 (so-called hamburger disease) can lead to chronic kidney failure or chronic bowel diseases. Some kinds of fish and shellfish poisonings result in chronic neurological and memory problems (that’s my excuse for forgetting things).

So, you have survived the journey; to paraphrase an ancient Persian saying, the fine wine of France has been transformed by the human body into urine, and the succulent cabbage rolls of Kiev have been transformed into fertilizer. Millions of bacteria have died. Millions more have been born. Whole civilizations have come and gone in the bowels of your body. Truly, a Wagnerian chorus could not match the richness of this drama.