effect of an imbalance in human-microbial relations, some distortion in our collective ecosystem, resulting in the migration of disease-causing microbes from their natural homes into our food, and from there into our bodies. More often than not, the ecosystem distortion or cause of the bacterial migration is human in origin. Perhaps the easiest way to explore foodborne infections as a complex social-ecological issue is to look closely at the emergence and behavior of Salmonella epidemics over the past few decades.
On June 24, 1984, a seventy-one-year-old lady went to a family picnic in Moncton, New Brunswick. Little did she know, when she ate her morsel of cheese, that she was to be part of a great Canadian historical event, celebrated in bacterial circles and rued in milk producers’ circles for many years to come. On June 27, this modest, grandmotherly woman came down with nausea and diarrhea. Although some folks have been known to react in similar fashion to family picnics, this woman did not think family events were quite that bad. On June 28, she started vomiting; by June 30, things were getting worse, and she ended up in the hospital, from which she emerged shaken but alive on July 5.
That same day, the cheese manufacturer, in Prince Edward Island, issued a national recall of its products, which were distributed across Canada under various brand names. What the woman in Moncton did not know was that she was near the tail end of a six-month epidemic of salmonellosis that attacked more than two thousand people in the Maritimes and Ontario. The investigation of this epidemic, the largest of its kind in Canada, had progressed more slowly than it should have for various reasons. Not all the investigators saw the value of sound epidemiologic methods and did not always include a comparison, or control group, in their investigations. Cheese was not always considered a real food by those who got sick; they thought of it as a snack and thus did not include it in their food history questionnaire. The cheese involved was distributed to most Canadian provinces under eighteen brand names, making it difficult to trace. Finally, the number of bacteria in the cheese was very low. One Canadian researcher estimated, based on a series of case studies, that people in this epidemic got sick by eating fewer than half a dozen of these microscopic bacteria.
The organism involved in this epidemic, a strain of Salmonella typhimurium, was traced back to the factory where the cheese was made. There, it turned out, one of the workers decided to turn off some valves manually, even though an electronically controlled flow-diversion valve was in place. As a result, raw milk that was supposed to go to the pasteurizer ended up in the cheese vat, and 2,700 people got sick. The milk with the Salmonella in it was traced to one teat on one cow on one farm. She was a good producer, but she had chronic mastitis, not caused by Salmonella, although she was shedding it.
Most of the agents that cause food poisoning have a natural home—that is, they have evolved a niche for themselves where, like most of us, they carry out their recycling and respiratory functions with minimal trauma to their immediate neighbors. Over the years, a high proportion of outbreaks of foodborne disease in Canada and the United States has been traced to chicken, turkey, pork, and beef. Other Salmonella prefer pigeons, gulls, and people.
As in any respectable family, there are a few black sheep and troublemakers that will stir up a good gut incident no matter where they are. However, in its natural home setting, Salmonella organisms, like most of the agents that cause foodborne disease, often live like good quiet farmers in the hinterlands of their chosen animal hosts. The Maritime cow with the bacteria dripping from her teat is typical.
That year, 1984, George Orwell’s year of doom, was a bad year for salmonellosis in Canada. In September 1984, for instance, the Pope helicoptered in to visit the Jesuit mission of Sainte-Marie among the Hurons near Midland, Ontario. Of the more than sixteen hundred police officers who provided security, five hundred ate the roast beef boxed lunch offered by volunteers. Within the next twenty-four hours, as they headed home, just about every one of those police officers got sick. Newspaper reports describe police sick with severe diarrhea and vomiting on buses and motorcycles, finding bathrooms where they could, running from squad cars into the woods. In the weeks that followed, twenty-seven (over 6 percent) of the infected officers developed reactive (secondary) arthritis—pain and swelling in many of their joints. Some of them ended up with permanent joint damage. This painful arthritis, which is sometimes associated with eye and urinary tract inflammation, is a known consequence of infections with foodborne organisms such as Salmonella, Campylobacter, and Yersinia. Reactive arthritis used to be called Reiter’s syndrome, after the physician who discovered it in 1916. Unfortunately, Dr. Reiter later went on to a less-than-glorious career doing experiments in the Nazi death camps—hence the new name for the disease.
The 1984 outbreaks in Canada were a sign of things to come from the Salmonella gang. In the spring of 1985, some 16,000 people in and around Chicago were reported to have acquired Salmonella-associated diarrhea and vomiting after a small technical mix-up in a dairy processing plant. After an intensive investigation, the estimate of casualties was raised to almost 200,000. Only a few months before, the plant had been hailed as one of the safest and most modern in the United States (and by implication, of course, the world). In this case the cause appeared to be a structural flaw in the technology itself, which, as in Prince Edward Island, had allowed some unpasteurized milk to slip into the system. After the epidemic the plant, the largest in U.S. history until then, went bankrupt.
In 1994 an estimated 224,000 people got sick from Salmonella typhimurium. Tanker trucks in Minnesota that had been carrying liquid raw eggs were subsequently used to haul ice cream premix. The tanks had apparently not been well cleaned out. All the eggs were in one basket and guess what? Somebody dropped it.
When I’m teaching, I like to tell the parallel story, which also took place in 1994, of the old Mennonite couple at the St. Jacobs farmers’ market who sold a homemade delicacy called cook cheese. Apparently, they didn’t properly clean out a barrel that had been used to store chickens. Eighty-two people got sick. It was big news locally. It was sad for the old couple, but the problem could be handled locally and provided an excellent opportunity for education. There are still many such small outbreaks around the world. The major advantage, from a public health point of view, is that you can identify the farms, talk to the farmers, and improve the situation with a few simple recommendations. Trace-backs, responses, and regulations are much more difficult at economies of scale; they require more sophisticated (and expensive) molecular laboratory techniques and tend to evoke industrial-type solutions, like food irradiation, which mostly increase problems rather than solve them.
Several other trends have emerged in recent years. First, even if they are not large, outbreaks of salmonellosis and other foodborne bacteria are becoming more widespread as they cross borders and oceans. We are in the midst of a Salmonella pandemic. Because of mass distribution of food, and because food from many sources gets mixed up, relabeled, and redistributed at various points in the system, outbreaks are more difficult to trace back to where they started. Second, even though the bacteria involved are considered to be adapted to animals, they are also being connected with fresh produce. The sh*t is everywhere: fresh sprouts of all sorts, cantaloupe, chip dips, minced beef, powdered milk, lettuce, tomatoes, and pigs’ ears (fed as treats to dogs that then infect people) are some of the sources of human infections. Finally, some of the newer strains of Salmonella are resistant to a wide variety of antibiotics.
Salmonella typhimurium DT104, which sounds like the name of a small warship, first emerged in cattle in the United Kingdom in the early 1980s and then went pandemic in the next couple of decades. This organism is more likely to kill both people and animals than other members of the Salmonella extended family and is resistant to most of the antibacterial drugs one might wish to launch against it. Fortunately, although it has become widespread in North America and Europe, it does not (yet) appear to be common.
Trying to understand the emergence and spread of Salmonella is a lesson in the complex dynamics of social-ecological systems we think we control. Although a few of them prefer one host (typhi in people, cholerae-suis in pigs), most Salmonella are both liberated and cosmopolitan. S. panama came into the United Kingdom by way of dried eggs during World War II and from there migrated into pig feed and from there into people. S. eastbourne rode the cocoa bean boats from Africa into eastern Canada and brought its sweet tenesmus