Perspectives from a Review of Selected Case Histories of Microbiological Problems with Imported Produce
At the 2001 American Society of Microbiology Annual Meeting in Orlando, FL, session, “Microbiology of Imported Foods: Oversight and Regulation:’ panelist Dean O. Cliver, Ph.D., University of California, Davis, School of Veterinary Medicine and member of the World Health Organization Collaborating Center for Food Virology, noted that the challenges of detecting and controlling harmful bacteria, viruses and protozoa on imported produce remain complex on both the scientific and regulatory fronts. However, some of the lessons learned from a review of selected case histories of foodborne illness outbreaks associated with produce that occurred in the U.S. and Canada over the past decade provide insight into how the produce industry might proceed in the face of these challenges.
“As far as imported food is concerned, what gets imported is based on the climate wherever the food is being grown and labor costs,” said Cliver. “Part of what is driving the market in the U.S. is that some people who claim to have credentials in nutrition are telling us that ‘fresh’ food is more nutritious than its counterpart that has been frozen or canned, but I consider that an unproven assertion. From a public health standpoint, what we’re talking about is foods that we eat raw.
“As a result of these drivers, we see a lot more fresh, or perishable, produce imported into the U.S., and while each commodity group has some idea of the flow of product into and out of the country, there really isn’t any way of knowing the rates of microbial contamination or incidence of foodborne illness associated with contamination of fresh fruits and vegetables,” he continued. “What typically happens is that when an exotic pathogen like Cyclospora rides in on a food, although relatively few people are affected, it suddenly becomes an international incident. It is blown out of proportion, but what proper proportion is, is anybody’s guess.”
The case histories selected by Cliver, were chosen with regard to whether they represented chronic or recurrent problems. A few instances of sporadic cases were noted. He described the following cases associated with cantaloupe, sprouts, raspberries, strawberries, parsley and mangoes:
• Cantaloupe. In June and July 1991, more than 400 illnesses in the U.S. and Canada were attributed to the contamination of these melons with Salmonella Poona. The melons were imported by Canada and allegedly originated from two Texas counties.
In May and June 1998, an outbreak of Salmonella Oranienburg was reported in Ontario, Canada, which caused 22 illnesses. The traceback investigation could not rule out the U.S. as a source of the cantaloupe, but noted that the countries of origin could also have been Mexico or a few Central American nations.
Most recently, in May 2001, an outbreak associated with cantaloupe imported into the U.S. by two Mexican companies caused approximately 30 illnesses involving eight U.S. states. The contaminant was identified as Salmonella Poona. Investigators were able to determine that the cantaloupe did not come from the U.S., because the harvest season had not yet begun.
• Sprouts. The venues for a 1994 outbreak of Salmonella Bovismorbificans-associated illnesses were Sweden and Finland. Some 282 illnesses were reported in Sweden and approximately 40 in Finland. It was determined that the alfalfa seeds were from Australia.
Salmonella Stanley was the culprit in a 1995 outbreak which affected Finland (28 illnesses) and the U.S. (128 illnesses), in which each shared a source and a serotype. In this case, the source was a broker in The Netherlands, although the alfalfa seed could have originated either in Italy, Hungary or Pakistan.
Also in 1995, Salmonella Newport in sprouts caused 133 illnesses in the state of Oregon and one Canadian province, British Columbia. Six other U.S. states also reported illnesses associated with these sprouts. The alfalfa seeds were traced to a broker in The Netherlands.
• Raspberries. One of the most notorious of international foodborne disease outbreaks involved a recurrent problem with Cyclospora cayetanensis in raspberries exported by Guatemala. In 1996, there were more than 1,465 illnesses reported in the U.S. and Canada; in 1997, both countries again experienced outbreaks. In 1998, the U.S. decided to embargo raspberries from Guatemala, but Canada did not and had another outbreak. (Cliver noted that this latter proved to be “one of the more elegant controlled experiments” in this type of outbreak. Even so, puzzles remain: “The oocysts of Cyclospora take days to weeks to sporulate and become infectious after they’re shed in feces, and there is no known alternate source on humans,” said Cliver “so how these got onto raspberries, which have very short shelf life, can’t be washed at source, and so on, is still very much a mystery.”)