Infections with several different bacteria were associated not only with increases in the short-term risk of death, but also with longer-term risks of up to one year.

"It's possible that those people who get foodborne infections are also people with severe underlying illness or who have a generally poor health status than most people, but we accounted for this problem and we still observed this excess mortality," says Dr. Kare Mølbak, the senior author of the study and a senior medical officer with the department of epidemiology at Statens Serum Institute in Copenhagen, Denmark.

"To our surprise, for some of the agents, the mortality risk was up to one year after the acute phase of the infection," Mølbak adds.

The study, which appears in the Feb. 15 issue of the British Medical Journal, comes on the heels of an announcement by U.S. Rep. Rosa L. DeLauro (D-Conn.) that that she was again co-sponsoring the Safe Food Act, which would create a single food-safety department out of the 19 existing U.S. departments and agencies. .

The U.S. Centers for Disease Control and Prevention estimates that foodborne diseases cause 76 million illnesses, 325,000 hospitalizations and 5,200 deaths each year. DeLauro, who contracted Salmonella poisoning as a child and was quarantined for two weeks, reports that 6.6 million pounds of potentially contaminated meat were recalled last year.

More than 250 foodborne diseases have been described, most of them caused by viruses, bacteria, or parasites.

This study looked specifically at four bacteria -- Salmonella, Campylobacter, Yersinia enterocolitica, and Shigella in 48,857 Danish people. This group was compared with 487,138 controls from the general population.

More than half (55.2 percent) of the patients in the foodborne-illness group were infected with Salmonella, one-third (33.1 percent) with Campylobacter, 8.3 percent with Yersinia enterocolitica, and 3.4 percent with Shigella.

Each of the four bacteria listed can cause diarrhea, cramping, abdominal pain, and fever. Most cases resolve on their own but some patients need further care and even hospitalization.

As a group, the people with a foodborne bacterial infection had a 3.1 times higher mortality than the controls. In total, 2.2 percent of the people who got gastrointestinal infections from the bacteria died within one year, compared with only 0.7 percent of the controls.

The mortality rate among those who contracted a specific strain called Salmonella dublin was 12 times higher than for the controls. For the other types of Salmonella, Campylobacter, and Yersinia enterocolitica, mortality was 1.86 to 2.88 times higher.

According to the study authors, the findings are more or less in line with existing fatality records for Yersinia but are higher than those previously reported for Salmonella, Campylobacter, and Shigella.

"There are a number of possible explanations," Mølbak says. Some of the patients may have had a relapse of the infection, even though it appeared to have cleared. Patients who had surgery may have had complications arising from the procedure.

"It makes perfect sense to me," says Dr. Philip Tierno, the director of clinical microbiology and immunology at New York University Medical Center and the author of The Secret Life of Germs and Protect Yourself Against Bioterrorism.

"When you understand how these agents cause disease in an individual, you realize that the lymph system is involved, your immune system obviously is involved. Maybe an allergic reaction might even occur," he says.

Dr. James Nataro, a professor of pediatrics, medicine and microbiology at the University of Maryland School of Medicine in Baltimore, is not so sure.

"Is it plausible that if you get diarrhea due to one of these organisms that there is an increased risk of death for six months to a year? Yes, it's plausible," he says. "That negative impact could make you susceptible to other unrelated diseases. But are we ready to accept the conclusions based on these data? I think we're very far from it."

It's possible that one underlying factor contributed both to the person contracting a foodborne bacteria and later dying, Nataro says.

Mølbak advises people who think they have a foodborne infection to seek medical attention. He also calls on food producers to use antibiotics sensibly, because the misuse of antibiotics can contribute to bacteria that are resistant to available drugs.

More information

The Centers for Disease Control and Prevention has information on Salmonella , on Campylobacter , on Shigella , and on Yersinia enterocolitica .