Food-Borne Pathogens

A food-borne illness is any illness resulting from the consumption of food. Most cases of food-borne illness are food infection caused by a variety of food-borne pathogenic bacteria, viruses, prions or parasites. Food-borne pathogens continue to cause major public health problems worldwide.

Why should I be aware of this?

They are the leading causes of illness and death in less developed countries, killing approximately 1.8 million people annually. In developed countries, these pathogens are responsible for millions of cases of infectious gastrointestinal diseases each year, costing billions of dollars in medical care and lost productivity. For instance, in 1994, an outbreak of Salmonellosis due to contaminated ice cream occurred in the US, affecting an estimated 224,000 persons. In 1988, an outbreak of Hepatitis A, resulting from the consumption of contaminated clams, affected nearly 300,000 individuals in China.

All about food-borne pathogens

Contamination of food usually arises from improper handling, preparation, or food storage. Good hygiene practices before, during, and after-food preparation can reduce the chances of contracting an illness. Food-borne disease can also be caused by a large variety of toxins that affect the environment.

Food handlers who are unwell are one of the most common sources of food-borne illnesses. Some common diseases are occasionally transmitted to food through water. These include infections caused by Shigella, Hepatitis A and the parasites Giardia lamblia and Cryptosporidium parvum. Food also gets contaminated when there is contact between food and pets. Flies, rodents, cockroaches and other pests are common causes of food contamination.

However, much is still not known about food-borne illnesses. Approximately 60 per cent of outbreaks are still caused by unknown sources.

Symptoms of food-borne illnesses

Symptoms may begin several hours to several days after ingestion, depending on the agent involved. These can include nausea, abdominal pain, vomiting, diarrhea, gastroenteritis, fever, headache or fatigue. In most cases, the body is able to recover after a short period of acute discomfort and illness. Sometimes, food-borne illnesses can result in permanent health problems or even death, especially in babies, pregnant women, the elderly, the sick and others with weak immune systems. Food-borne illnesses are also a major cause of reactive arthritis, which typically occurs one to three weeks after the infection. People with liver disease are especially susceptible to infections from Vibrio vulnificus, which can be found in oysters and crabs. Typically, food poisoning is evident when uncooked or unprepared food is eaten.

Incubation period

The delay between consumption of a contaminated food and the appearance of the symptoms of the illness is called the incubation period. This ranges from hours to days, depending on the agent and on how much food was consumed. During the incubation period, microbes pass through the stomach into the intestine and attach themselves to the cells lining the intestinal walls. Here they begin to multiply. Some kinds of microbes stay in the intestine, while some produce a toxin that is absorbed into the bloodstream. Others directly invade the deeper body tissues. The symptoms produced depend on the type of microbe. The common bacterial food-borne pathogens are:

• Bacillus cereus
• Campylobacter jejuni, which can lead to secondary Guillain-Barré syndrome
• Escherichia coli O157:H7 enterohemorrhagic (EHEC), which causes hemolytic-uremic syndrome
• Escherichia coli - enteroinvasive (EIEC)
• Escherichia coli - enteropathogenic (EPEC)
• Escherichia coli - enterotoxigenic (ETEC)
• Escherichia coli - enteroaggregative (EAEC or EAgEC)
• Listeria monocytogenes
• Salmonella spp.
• Shigella spp.
• Streptococcus
• Vibrio cholerae, including O1 and non-O1
• Vibrio parahaemolyticus
• Vibrio vulnificus
• Yersinia enterocolitica and Yersinia pseudotuberculosis

The lesser-known bacterial agents are:

• Brucella spp.
• Corynebacterium ulcerans
• Coxiella burnetii or Q fever
• Plesiomonas shigelloides

In addition to diseases caused by direct bacterial infection, some food-borne illnesses are caused by exotoxins, which are excreted by the cell as the bacterium grows. Exotoxins can produce illness even when the microbes that produced them have been killed. Symptoms typically appear after one to six hours, depending on the amount of toxin ingested. For example, Staphylococcus aureus produces a toxin that causes intense vomiting. The rare—but potentially deadly—disease, botulism, occurs when the anaerobic bacterium Clostridium botulinum grows in improperly canned low-acid foods and produces botulin, a powerful paralytic toxin.

What can I do?

Prevention

Prevention of food-borne illnesses is mainly through the definition of strict rules of hygiene with regard to the veterinary sector of the food chain, from farming to delivery (shops and restaurants). This regulation includes:

• In a final product, it must be possible to know the origin of the ingredients (originating farm, identification of the harvesting or of the animal) and where and when it was processed; the origin of the illness can thus be tracked and solved (and possibly penalised), and the final products can be removed from the sale if a problem is detected.
• Respect of hygiene procedures.
• Power of control and of law enforcement of the veterinarians.

Safety practices at home

At home, prevention mainly consists of good food safety practices which include:

• Separating foods while preparing and storing to prevent cross-contamination—that is, clean cutting boards, utensils, and hands after handling meat and before cutting vegetables.
• Washing hands and/or latex gloves before handling ready-to-eat foods.
• Not preparing food when sick or recovering from recent illness.
• Respecting food storage methods (hot foods hot and cold foods cold) and food preservation methods (especially refrigeration), and checking the expiration date.
• Avoiding over-long storage of left-overs.
• Washing hands before preparing a meal and before eating.
• Washing fresh fruit and vegetables with clear water, especially when not cooked (fruit and salads), scrubbing firm fruits and vegetables with a brush to clean.
• Washing dishes after use, rinsing them well in hot water and storing them clean and dry.
• Keeping work surfaces and chopping boards clean and dry.
• Keeping kitchen and cooking utensils clean and dry.
• Not relying on disinfectants or disinfectant-impregnated cloths and surfaces as a substitute for good hygiene methodology (as above).
• Preventing pets walking on food-preparation surfaces.

References

• Foodsafety.gov
• Campylobacter jejuni—An Emerging Foodborne Pathogen
• Horizon Scientific Press
• Electroimmunoassay technology for food-borne-pathogen detection