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.