Colette Dziadul struggled for years to understand her daughter’s joint problems. Dana, who is now 14 years old, complained from toddlerhood that her knees and ankles hurt. The aches kept her up at night, made her wake her parents to ask for painkillers and forced her to sit out school sports. Nevertheless, two pediatricians and an orthopedist diagnosed the problem as “growing pains” that would fade as she grew older.

Then, when Dana was 11, Dziadul participated in a survey about foodborne illness. The questionnaire came from an organization called Safe Tables Our Priority (now STOP Foodborne Illness), which was canvassing survivors of outbreaks for details of their recoveries. When she was three years old, Dana had spent two weeks in the hospital—one of 50 people sickened after eating cantaloupe that had been contaminated with Salmonella. Among the complications of infection that the survey listed were symptoms of a form of joint damage known as reactive arthritis.

Dziadul was dumbfounded. She found Dana a rheumatologist, who confirmed that the pain was caused by arthritis for which there was no other explanation. Then she went back into Dana’s medical records. On Dana’s 10th day in the hospital a nurse had recorded that the youngster was limping and complaining of joint pain. Could those long-forgotten symptoms have been the first sign of arthritis, starting as her body reacted to the Salmonella infection? “That there could be a connection between Salmonella and arthritis never crossed my mind,”

Dziadul says. “And it never crossed most of the doctors’ minds.”

It is a scary idea that food poisoning—which we think of as lasting just a few days—could instead have lifelong aftereffects. The incidence of such “sequelae,” in medical parlance, has been thought to be low, but not many researchers studied the problem until recently. New findings by several scientific teams suggest the phenomenon is more common than anyone thought.

A Common Problem?

Foodborne disease has an enormous public health impact even if you count only the initial, acute episodes of illness. The Centers for Disease Control and Prevention estimated in 2011 that the U.S. sees 48 million illnesses, 128,000 hospitalizations and 3,000 deaths every year from foodborne organisms. (The European Union had 48,964 cases and 46 deaths in 2009, the most recent year tallied.) The U.S. Department of Agriculture’s Economic Research Service calculates the cost of foodborne illnesses just from bacterial infection to be at least $6.7 billion, counting medical care, premature deaths and lost productivity. Re­searchers who attempt to track chronic effects say that the actual bill is much higher.

“People don’t understand the full consequences of foodborne disease,” says Kirk Smith of the Minnesota Department of Health, which lends its investigators around the U.S. “They think you get diarrhea for a few days and then you are better. They don’t understand that there is a whole range of chronic sequelae. And although any of them may not be common individually, when you put them together they add up to a lot.”

Long-term consequences are not limited to individuals who were hospitalized, as Dana was. They have also been recorded in people who experienced what seemed to be minor bouts of fever, vomiting or diarrhea. The consequences include reactive arthritis, urinary tract problems and damage to the eyes after Salmonella and Shigella infections; Guillain-Barré syndrome and ulcerative colitis (a chronic bowel inflammation) after Campylobacter infection; and kidney failure and diabetes after infection with Escherichia coli O157:H7. Those organisms are very common: federal investigators have identified them in meat, milk, poultry, eggs, seafood, fruit, vegetables and even processed foods.

As researchers look back at foodborne outbreaks, they are not only confirming that these complications appear in survivors but adding to the list of illnesses that may occur. A survey of 101,855 residents of Sweden who were made sick by food between 1997 and 2004 found, for instance, that they had higher-than-normal rates of aortic aneurysms, ulcerative colitis and reactive arthritis. A review of a major provincial health database in Australia revealed that people there who contracted any bacterial gastrointestinal infection were 57 percent more likely to develop either ulcerative colitis or Crohn’s disease, another chronic bowel condition, than people born in the same place and era who had not had such infections. And several years after a 2005 outbreak of Salmonella in Spain, 65 percent of 248 victims said they had developed joint or muscle pain or stiffness, compared with 24 percent of a control group who were not affected by the outbreak.

Few comprehensive analyses have been conducted in the U.S. Traditionally, food-related investigations have aimed at finding and interviewing victims during the outbreak, Smith says. Because acute illness lasts a couple of weeks at most, little attention has been paid to keeping track of victims afterward—something that might be very complicated because they may go to different doctors and even live in different states.

One of the U.S. studies, published in 2008, traced victims of foodborne illness in Minnesota and Oregon between 2002 and 2004. Researchers determined whom to contact based on rec­ords collected by a CDC surveillance project known as the Foodborne Diseases Active Surveillance Network (FoodNet), which collects reports of lab-confirmed infections caused by 10 different organisms. Out of 4,468 victims, 575 (13 percent) reported later symptoms that matched reactive arthritis, although most—unlike Dana—were never diagnosed by a specialist.

The link between foodborne illness and long-term health consequences could be a coincidence, although advocates say that the chances are remote. A better way to prove the connection would be to identify victims when they first become ill and track them for years thereafter, a research arrangement called a prospective study. There are a few such studies worldwide, and a recently concluded one—the only one to take place in North America—was stunning and persuasive.

In May 2000 the drinking water in Walkerton, Ont., became contaminated with E. coli O157 after heavy rains washed manure from farm fields into its aquifer. More than 2,300 people, about half the town’s population, developed fever and diarrhea soon afterward. In 2002 the Ontario government funded the Walkerton Health Study to assess any health effects that might persist among the victims. In 2010 the study published its findings: compared with residents who did not get very sick, those who endured several days of diarrhea during the outbreak had a 33 percent greater likelihood of developing high blood pressure, a 210 percent greater risk of heart attack or stroke, and a 340 percent greater risk of kidney problems in the eight years following the outbreak.

Those outcomes were not limited to people who developed the most serious consequences of E. coli O157 infection. Even Walkerton residents with milder symptoms experienced circulatory problems that would not have been linked to E. coli without the prospective monitoring. That discovery suggests how common the late-onset effects of E. coli infection might be, says William F. Clark, the study’s leader and a professor of nephrology at the University of Western Ontario. Clark recommends that survivors of such illnesses have their blood pressure checked every year and their kidney function checked every two or three years.

Given how few scientists have studied the issue, most of the problems have come to light thanks to patient advocacy groups. STOP’s original survey, in which Colette Dziadul participated, collected first-person accounts from patients. It was followed by a 2009 white paper from the nonprofit Center for Foodborne Illness Research and Prevention, which unearthed research on long-term sequelae that were buried in the medical literature.

That group now has a grant from the U.S. Food and Drug Administration to research how best to study the frequency of persistent aftereffects. Advocates want public health agencies to create better mechanisms for identifying and tracking victims, and like Clark, they think victims should be connected as soon as possible to preventive medical care.

“We want to establish the true burden of disease because that is what policy makers use to decide what is a public health priority,” says Barbara Kowalcyk, the center’s co-founder. “As long as we focus only on the acute form of foodborne illness and not the long-term health consequences, we’ll underestimate how significant a problem this is.”