Food Poisoning Traced to Deer-Soiled Lettuce
Date: 12-Mar-04
Country: USA
Though common in certain animals, Y. pseudotuberculosis infects humans relatively rarely, according to the authors of an article in the current issue of the Journal of Infectious Diseases. The infection causes fever and abdominal pain that can be confused with symptoms of acute appendicitis.
Scientists have long suspected that contaminated food causes human infections, but until now no outbreak had been tied to a specific food source.
The Finnish outbreak sickened at least 47 people nationwide in October 1998, prompting a long-term investigation by public health authorities that ultimately pinpointed the source as iceberg lettuce from a single farm.
Dr. J. Pekka Nuorti and colleagues at the National Public Health Institute and National Food Agency in Helsinki suspect that the lettuce was contaminated by deer feces harboring Y. pseudotuberculosis.
Through interviews with 38 people who were infected during the outbreak, the researchers found that nearly three-quarters had eaten iceberg lettuce during the two weeks before they fell ill.
Nuorti's team traced clusters of the infection back to four school and workplace cafeterias, which eventually led them to four farms that supplied the cafeterias with lettuce. By that time, no suspect lettuce was available for testing, but the researchers monitored the farms through 2000, ultimately finding Y. pseudotuberculosis in samples of lettuce, soil and irrigation water on one farm.
The researchers also discovered "large quantities" of deer feces around the lettuce fields and irrigation-water sources, which were unfenced. Deer commonly carry Y. pseudotuberculosis, Nuorti's team notes in the report.
The Finnish outbreak adds to the growing recognition of fresh produce as a potential source of foodborne illness, Dr. Robert V. Tauxe of the U.S. Centers for Disease Control and Prevention writes in an accompanying editorial.
In recent years, he notes, lettuce and other produce such as tomatoes, raspberries and parsley have triggered outbreaks of E. coli and other infections in a number of countries.
Lettuce, according to the Finnish researchers, may be a particularly good "vehicle" for bacteria because it has a large surface area, can be difficult to clean and is almost always eaten raw.
In general, there is little consumers can do to protect themselves from tainted, uncooked produce, Tauxe points out. Washing fruits and vegetables is "prudent," he notes, but it cuts surface contamination only to a limited degree.
Instead, he writes, contamination has to be prevented from the field onward. If deer or other animals were indeed the culprit in the Finnish outbreak, Tauxe adds, prevention may include fencing in fields and controlling the animal population.