Bugs in our meal: Food for thought

The purpose of this statement is to provide practical guidance to physicians who counsel patients on food safety. Food safety has become an important public health issue in North America. In 1999, the Canadian government announced that $65 million would be spent to improve the safety of Canada’s food supply. The funds would be used to improve scientific programs, surveillance and the regulatory framework relating to food safety (1). A 1995 Canadian consensus conference made a series of recommendations for improving surveillance capacity in the area of food- and waterborne infections (2). In the United States, former president Bill Clinton announced a food safety initiative that involved targeting $43 million for the 1998 fiscal year (3). The goal of the effort is “to reduce, to the greatest extent possible, the incidence of foodborne illness in the United States by reviewing and updating the existing early warning systems, enhancing seafood safety, and expanding research on such aspects of food safety as risk assessment, training, and education” (3). A sentinel system for active population-based foodborne disease surveillance (FoodNet <http://www.cdc.gov/foodnet>) and a laboratory-based, enteric pathogen molecular typing network were recently established in the United States (4,5).

BACKGROUND

Why is food safety such an important issue? There are many reasons. The number of reported cases of enteric infections (most of which are foodborne) has increased steadily in many countries (6). Among the public and in the media, there has been growing concern about foodborne outbreaks, although an actual increase has not been observed through passive surveillance in Canada (7). New pathogens have emerged (Cyclospora cayetanensis) or have been recognized as being causes of foodborne disease (eg, Campylobacter species, Echerichia coli 0157:H7, caliciviruses) (8).

A prime example of a disease caused by an emerging pathogen is variant Creutzfeld-Jakob disease (vCJD) (9–11). In the early 1980s, an epidemic of transmissible spongiform encephalopathy in bovines (BSE) occurred in the United Kingdom because of changes in production methods of commercial feedlots (9,10). The first cases of BSE appeared in 1986, and the incidence of the disease peaked in 1993. Over 165,000 cases were documented in cattle. This epidemic has been controlled through changes in regulations concerning the production of feedlots and by culling infected herds. The first case of vCJD, a fatal illness causing dementia in humans, was reported in 1996 (11). Since then, over 40 cases of vCJD have been reported, and all but two cases involved residents of the United Kingdom. Recent evidence clearly shows that the agents of BSE and vCJD are very similar or identical. Therefore, it appears that patients with vCJD acquired the disease from infected cattle, most probably from eating contaminated beef products. Fortunately, BSE has not emerged as a problem in North America, and no case of vCJD has yet been reported in North America.

The population of immunocompromized patients who are highly susceptible to enteric pathogens has increased (12). Enteric pathogens can cause severe extra-intestinal organ injury. Examples of such conditions include hemolytic uremic syndrome following E coli 0157:H7 gastroenteritis, Guillain-Barré syndrome after Campylobacter enteritis (13), and invasive listeria infections in pregnant women and immunocompromized hosts. Finally, many enteric pathogens are becoming resistant to antimicrobials used during therapy (8).

Traditionally, vehicles for the transmission of foodborne infections included undercooked meat, poultry or seafood, and unpasteurized milk. Uncracked eggs were considered safe. However, it is now well recognized that when Salmonella enteritidis is endemic in egg-laying flocks, it can contaminate intact eggs. Inadequately cooked eggs have become a significant cause of foodborne outbreaks. Fresh fruits and vegetables are increasingly reported as the cause of foodborne outbreaks. Contaminated alfalfa sprouts, imported raspberries, tomatoes, cantaloupes, scallions and leaf lettuce have all been implicated in foodborne outbreaks. Unpasteurized apple juice, cider and orange juice have also recently been implicated in outbreaks (8). Table 1 summarizes the main food items that have been associated with the transmission of foodborne illnesses and the principal microorganisms involved.

TABLE 1:

Potentially contaminated food products

Food	Major organism involved	Recommendation
Unpasteurized milk and cheese	Salmonella, Campylobacter, Escherichia coli 0157:H7, Listeria	Children should not drink unpasteurized milk or eat unpasteurized soft cheeses (cheeses that go through a maturing process of 60 days or more are safe)
Unpasteurized juices	E coli 0157:H7, Salmonella	Children should only drink pasteurized juice products unless the fruit is washed and freshly squeezed (ie, orange juice) immediately before consumption
Eggs	Salmonella	Children should not eat raw or undercooked eggs, unpasteurized powdered eggs or products containing raw eggs
Raw and undercooked meat	Salmonella, Campylobacter, E coli 0157:H7, Trichinosis, Listeria, Brucella, Toxoplasma gondii	Children should not eat raw or undercooked meat or meat products (including hot dogs)
Alfalfa sprouts	Salmonella, E coli 0157:H7	Children should avoid eating alfalfa sprouts
Fresh fruits and vegetables	Cryptosporidium, Cyclospora, calicivirus, Giardia lamblia, Shigella, E coli species	All fruits and vegetables should be cleaned before ingestion
Raw fish and shell fish	Many pathogens, toxins and parasites	Many experts recommend that children not eat raw oysters. Some experts caution against ingesting raw fish
Honey	Clostridium botulinum	Children younger than one year of age should not be given honey unless the product has been certified to be free of C botulinum spores

ENVIRONMENTAL FACTORS

What are the fundamental environmental causes of foodborne illnesses? Consumers have moved away from a traditional ‘meat and potatoes’ diet, and are eating more fresh fruits and vegetables, salads and grains (foods that are considered to be a part of a healthier diet). The demand for fresh produce all year round has resulted in increased consumption of produce that is imported from countries where the methods of production are not as well controlled as in Canada (8). Because much of the fresh produce consumed by Canadians is imported, special care should be taken when washing and/or peeling produce before eating it uncooked. Furthermore, consumers are eating prepared foods more often (both at home and outside of the home), and frequently buy ready-to-eat meals at restaurants or deli counters of grocery stores (14). The mass production of foods and increasing international trade in foods are also important contributing factors to the problem of food safety.

The responsibility for food safety is shared by the food industry, public health agencies and consumers. Issues surrounding food safety that relate to the food industry and public health are beyond the scope of this statement. However, consumers are important players in promoting food safety, and this statement addresses the role that treating physicians can play in educating consumers. Consumers are increasingly concerned about food safety, but are not knowledgeable about safe food preparation practices in the home (14,15). Most consumers believe that foodborne illnesses are acquired more often outside of the home, whereas most infections occur in a home setting (15).

COUNSELLING TIPS

Primary care physicians have a role to play in promoting food safety. They can educate consumers about safe (and unsafe) foods, and safe food preparation practices. A physician’s advice is a powerful determinant of patient behaviour.

What are the important messages that physicians should transmit? The World Health Organization has prepared a series of 10 rules endorsed by the Canadian Paediatric Society, to ensure that food served at home is as safe as possible (16).

1. Choose foods that are as safe as they can be. Unpasteurized milk and unpasteurized fruit juices (unless freshly squeezed immediately before consumption) are inherently unsafe, and without a noticeably improved nutritional value. Fresh fruits and vegetables can also be contaminated. It is important to wash fresh fruits and vegetables carefully, especially if they are to be eaten uncooked.

2. Cook foods thoroughly. Raw meat, particularly poultry, is often contaminated with disease-causing microorganisms. Cooking these foods until they are steaming hot will ensure that most contaminating microorganisms are destroyed. It is particularly important to cook ground beef thoroughly (until it is no longer pink on the inside and the juices run clear) because inadequately cooked ground beef can cause E coli 0157:H7 enteritis and hemolytic uremic syndrome. Eggs should be thoroughly cooked because raw or undercooked eggs can transmit Salmonella.

3. Eat foods soon after they are cooked. Cooked foods should be consumed as soon as they are cooked. Setting foods aside to cool at room temperature runs the risk of permitting the proliferation of residual microorganisms. If cooked foods are to be stored for later consumption, they should be rapidly cooled to a temperature (around 4°C) to impede bacterial growth. (See recommendation 5.)

4. Avoid contact between raw and cooked foods. Examples include contact between uncooked and cooked meat, and contact between uncooked meat and foods that will be consumed uncooked (eg, fruits and vegetables). Cooked food can become contaminated through even casual contact with raw food. The cross-contamination can be direct or indirect (by contaminated cutting utensils, chopping boards and unwashed hands). Thus, it is important to wash hands, utensils, chopping boards and work surfaces carefully after manipulating raw food.

5. Store cooked foods appropriately. Once cooked, foods must be kept at 60°C or rapidly cooled and stored at 4°C to avoid proliferation of residual microorganisms. Safe storage practices are particularly important for susceptible populations such as infants, toddlers and immunocompromised individuals.

6. Reheat cooked foods adequately. If cooked food is to be reheated before consumption, an adequate temperature must be reached to destroy any microbial regrowth that occurred during storage. If you use a microwave oven, ensure that the food has reached a uniformly adequate temperature.

7. Wash hands frequently. Hands should be washed carefully with soap and water before starting food preparation. Also, hands should be washed after manipulating raw food, especially meat and poultry. Hands should be washed especially after going to the bathroom, changing diapers and touching pets.

8. Keep the kitchen meticulously clean. Food debris can sustain microbial proliferation.

9. Protect foods from insects, rodents and other animals (including pets) that can be carriers of pathogenic microorganisms. Store nonperishable foods in a safe place.

10. Always use safe water for food preparation and consumption.

IMMUNOCOMPROMISED PATIENTS

Physicians should give additional advice to parents of children who are immunocompromised because of underlying disease or therapy. These patients are at increased risk of severe disease following the acquisition of foodborne microorganisms. Toxoplasma gondii, Cryptosporidium parvum, Salmonella species and Listeria monocytogenes are only some of the agents that can cause severe disease in these patients. Therefore, special additional precautions should be taken in selecting and preparing foods for these patients. Red meat should be thoroughly cooked. These patients should avoid processed meat and unpasteurized cheeses. Emphasize the appropriate preparation of produce, such as fresh fruits and vegetables, that is intended to be eaten uncooked. Such foods should be carefully washed and peeled before consumption. Foods that cannot be adequately decontaminated should be avoided. More detailed recommendations on preventing foodborne illnesses in individuals with the human immunodeficiency virus (HIV) have been published; interested readers should consult the 1999 United States Public Health Service and Infectious Disease Society of America Guidelines for the Prevention of Opportunistic Infections in Persons Infected with Human Immunodeficiency Virus (17). In addition, the United States-based Centers for Disease Control have produced a guide on safe water and food for HIV-infected persons (18). Much of the advice directed at HIV-infected individuals is pertinent to other patients who are immunocompromized because of illness or therapy.

IRRADIATED FOODS

Some parents may ask about the safety of irradiated foods. A recent review of this topic has been published (19). In a well regulated environment where irradiation dose levels are controlled, food irradiation is a safe procedure that can enhance food safety by eliminating residual levels of microbial pathogens. It is not a substitute for appropriate food production, processing and preparation. Irradiated food is safe, nutritious and produces no unusual toxicity – as long as good management practices are followed. There is no risk of ingesting a radioactive substance when eating irradiated food. Knowledge about irradiated foods is evolving, and physicians must keep abreast of new information.