FOOD IRRADIATION; ARE WE READY FOR IT

by Dr. Moshe Ipp October 1997

The recent outbreak of a cyclosporiasis associated diarrhea in Canada and the USA, which resulted from the ingestion of imported raspberries from Guatemala has raised serious questions about the prevention of food borne diseases. Before 1997 most documented cases of cyclosporiasis in North America were in overseas travelers. The occurrence of 1465 cases of raspberry associated cyclosporiasis in the USA and Canada in 1996 has definitively established that cyclospora can be a food borne pathogen and that one does not need to leave home to contract this organism or many other exotic pathogens.

What has contributed to the changing epidemiological characteristics of food borne disease in North American?

The two major contributing factors to the increased occurrence of food borne disease are related to the globalization of food supply and the substantial alteration in the diet of North Americans over the past two decades. It is ironical that the promotion of a healthy diet including the recommendation to eat fruits and vegetables in particular, may have contributed to the improvement of cardiovascular health but has led to a significantly increased incidence of gastrointestinal diseases. It is estimated that up to 70% of selected fruits and vegetables consumed in North America come from developing countries. In fact raspberries were not planted in Guatemala until 1987, yet by May of 1996, 20% of all fresh raspberries sold in the United States came from Guatemala. Of the 1465 laboratory-confirmed and probable cases of cyclosporiasis, 195 cases originated in Canada, primarily in Ontario.

What is cyclospora, who is at risk for infection and what are the symptoms?

Cyclospora cayetanenesis is a parasite composed of one cell that is 8-10 microns in diameter. The first known case of cyclospora infection was diagnosed in 1977. Persons of all ages are at risk for infection. Cyclospora infects the small intestine and typically causes watery diarrhea with frequent stools. It should be suspected in any patient presenting with a diarrheal illness of 5 or more days duration associated with severe fatigue, loss of appetite and weight loss. Cyclosporiasis should be suspected regardless of whether the patient has traveled to a foreign country or consumed contaminated water. Physicians may need to specifically request identification of cyclospora since this may not be routinely performed in most clinical laboratories. The infection is treated with Trimethoprim/sulfamethoxazole.

What other recent outbreaks have been associated with food borne pathogens?

There have been recent reports of outbreaks of serious diarrheal illnesses associated with the consumption of raw milk, domestic cheeses, eggs, and commercial airline food. Powdered milk products and infant formula have also been contaminated with diarrhea-causing bacteria. Seafood has increasingly been implicated as the source of infectious disease outbreaks due to hepatitis A virus, Norwalk virus, vibrio species and clostridium botulinum. There have also been reports of outbreaks of gastrointestinal illnesses due to contaminated municipal water such as the occurrence of cryptosporidiosis in Milwaukee in April of 1993 that affected several hundreds of thousands of people. Hamburgers are another commonly consumed food and in 1993 there was a massive multi-state outbreak of "E. Coli" 0157:87 associated bloody diarrhea and hemolytic uremic syndrome. It is estimated that over 500 children and adults became ill from eating contaminated hamburger meat and 4 children died in this outbreak. As recently as August, 1997, all of the frozen hamburger meat in one US meat plant was recalled because of possible contamination with E. Coli and in another report alfalfa sprouts were found to be contaminated for the first time with E. Coli after a number of individuals became ill after ingesting the sprouts.

How can food borne illnesses be prevented?

Basic precautions include the avoidance of consumption of raw beef, unpasteurized milk and unchlorinated water. Fruits and vegetables should be washed thoroughly before ingestion. Problems exist with certain foods such as raspberries for example which once contaminated remain contaminated until eaten because they are too fragile and replete with crevices to be washed thoroughly. The exact mechanism whereby raspberries become contaminated with cyclospora is not known. The importance of knowing how berries and other foods become contaminated is vital when it comes to prevention. Contaminated water has been suggested as one of the main sources of contamination, however recently there has been consideration given to the role played by birds and other animals in the contamination of these berries and other fruits and vegetables. If indeed birds are responsible for the contamination of berries in Guatemala then the use of high-quality water for irrigation and pesticide spraying will not solve the problem of cyclospora contamination. Similarly if alfalfa sprouts are contaminated with E. Coli from animal droppings while at the seedling stage then no amount of washing will eliminate the imbedded organisms.

How else can food borne illnesses be prevented?

Although many new initiatives to improve the safety of our food supply have been put in place, primarily to improve the ability to detect food borne outbreaks, what is clearly needed is a mechanism to prevent the infection in the first place. The use of ionizing radiation for food pasteurization has been extensively evaluated and supported by the World Health Organization, the International Atomic Energy Agency and various other international agencies, scientists and government officials. It appears that irradiation provides the greatest likelihood of substantially reducing bacterial and parasitic causes of food borne diseases associated with numerous foods including fresh fruits and vegetables. Concern remains however, largely by activist groups, who are concerned that irradiation is unsafe and may seriously compromise the quality of the irradiated food. As we move into the 21St century the use of high tech state-of-the-art irradiation of the food that we eat may well be the way of the future.

References

1. New England J Med 336: No 22, 1597-99, 1997

2. Clin Infect Dis 18: 671-82, 1994.

3. Globe & Mail August 16, 1997.