Table of Contents
Yersinia is a bacterium that can contaminate food and is responsible for a foodborne disease called yersiniosis.
Yersinia is a serious issue because it contributes to waterborne and foodborne diseases that each year affect an estimated seventy-six million people in the United States. Awareness of potential sources of food contamination and knowledge of preventive measures is an important factor for maintaining health.
The genus Yersinia consists of 11 species of gram-negative bacilli. Yersinia enterocolitica, Yersinia pseudotuberculosis, and Yersinia pestis are the three disease-causing (pathogen) species.
Yersinia pestis causes plague and people usually get it from being bitten by a rodent flea that is a carrier or by handling an infected animal. Millions of people in Europe died from plague in the Middle Ages, carried by flea-infested rats. Nowadays, antibiotics are used effectively against plague, but if an infected person is not treated promptly, the disease is likely to cause illness or death. In the United States, the last plague epidemic occurred in Los Angeles in 1924–25. Since then, plague has occurred as a few scattered cases in rural areas, at an average rate of 10 to 15 persons each year.
Fifteen pathogenic O groups of Y. enterocolitica have been identified with serotype O:3 now predominating as the most common type in the United States.
Y. enterocolitica infections are uncommon in the United States. According to the Foodborne Disease Active Surveillance Network (FoodNet), the annual incidence per 100,000 people is 9.6 for infants, 1.4 for young children, and 0.2 for other age groups. Y. pseudotuberculosis infections are even more rare. Y. enterocolitica is mostly found in swine and Y. pseudotuber-culosis has been reported in deer, elk, goats, sheep, cattle, rats, squirrels, beaver, rabbits, and many bird species. To date however, no foodborne outbreaks caused by Y. pseudotuberculosis have been reported in the United States.
Y. enterocolitica infections cause yersiniosis, a disease with a variety of symptoms depending on the age of the person infected. In children, common symptoms are fever, abdominal pain, and diarrhea, which is often bloody. Yersinia infections are transmitted by eating contaminated food, such as raw or incompletely cooked pork products and unpasteurized milk, by contaminated water, by contact with infected animals, by transfusion with contaminated blood, and rarely from person-to-person. The incubation period usually varies between 4 to 6 days. The exact cause of the food contamination is unknown, but prevalence of the organism in the soil and water and in animals such as beavers, pigs, and squirrels, allows it to enter the food supply chain. Y. enterocolitica outbreaks documented at the Center for Disease Control (CDC) include:
- 1976: Chocolate milk outbreak in Oneida County, NY. involving school children.
- December 1981-February 1982: Outbreak in King County, WA, caused by ingestion of tofu. Investigators from the Food and Drug Administration (FDA) identified the source of the infection to be an non-chlorinated water supply.
- 1982. Outbreaks in Arkansas, Tennessee, and Mississippi due to the consumption of pasteurized milk. FDA investigators identified the infection source to be contaminated milk containers.
- 1995. Outbreak in the Upper Valley of Vermont and New Hampshire. This outbreak likely resulted from post-pasteurization contamination of milk. Dairy pigs were the most likely source of contamination. Milk bottles were also likely contaminated by rinsing with untreated well water prior to filling.
Poor sanitation and improper sterilization techniques by food handlers, including improper storage, are important factors contributing to contamination. To prevent yersinia outbreaks, the Center for Disease Control (CDC) offers the following preventive advice:
- Avoid eating raw or undercooked pork.
- Consume only pasteurized milk or milk products.
- Wash hands with soap and water before eating and preparing food, after contact with animals, and after handling raw meat.
- After handling raw chitterlings, clean hands and fingernails scrupulously with soap and water before touching infants or their toys, bottles, or pacifiers. A person other than the foodhandler should care for children while chitterlings are being prepared.
- Prevent cross-contamination in the kitchen by using separate cutting boards for meat and other foods, and carefully cleaning all cutting boards, countertops, and utensils with soap and hot water after preparing raw meat.
- Dispose of animal feces in a sanitary manner.
As long as the bacteria continues to be excreted, yersiniosis can be transmitted to others and accordingly requires strict attention to personal hygiene. People with yersiniosis should stay off work or school while they have symptoms. Those in high risk groups or occupations (infants, children, school pupils, students, food workers, child-care workers, teachers, and health care practitioners) can only return to work after being completely free of symptoms for two days.
Uncomplicated cases of Y. enterocolitica diarrhea usually resolve on their own without antibiotic treatment. However, in more severe or complicated infections, antibiotics may be required. Diarrhea is a symptom that is not only uncomfortable, but also dangerous to health, because it can result in the body loosing too much fluid (dehydration) and the salts and minerals (electrolytes) required to maintain health. Medicines that stop diarrhea are not recommended because diarrhea helps to purge the pathogen. To prevent dehydration and replenish lost electrolytes, a bland diet should be followed. Typically, it involves:
- Day 1: Drinking clear liquids at room temperature such as sports drinks (Powerade/Gatorade), weak tea (decaffeinated), non-caffeinated sodas;
- Day 2: Slowly adding bland foods in small amounts as can be tolerated during the day. Examples are: oatmeal or cream of wheat made with water, dry cereal (without milk), plain rice or pasta (no butter, oil, or sauces), crackers or pretzels, gingersnaps, plain toast (no butter or jelly), mashed potatoes (no skins), ripe bananas, applesauce, chicken noodle soup.
- Day 3: Gradually adding more variety of foods in small, more frequent meals evenly spaced throughout the day. Examples are: soft boiled eggs or scrambled eggs, plain baked potato, fish or chicken (no skin) well-cooked, baked or grilled (not fried), plain yogurt, cottage cheese, cooked carrots or green beans, milk (skim or low-fat after diarrhea has stopped).
The major complication of yersiniosis is the performance of unnecessary appendix removals (appendectomies) since one of the main symptoms of yersinia infections is abdominal pain of the lower right abdomen.
As a result, it is often misdiagnosed as appendicitis. In some cases, Y. enterocolitica and Y. pseudotuberculosis infections have also been followed by arthritis. Another possible rare complication is bacteremia, the entrance of the bacteria into the blood stream.
Besides ensuring that food is properly handled in the home so as to avoid yersinia contamination, parents should know that Federal Agencies provide detailed yersinia information to the general public. The Centers for Disease Control and Prevention (CDC) monitors the frequency of Y. enterocolitica infections through its Foodborne Disease Active Surveillance Network (FoodNet). CDC also investigates outbreaks to control them and to learn more about how to prevent these infections. It also promotes educational campaigns to increase public awareness about prevention measures. The United States Food and Drug Administration (FDA) inspects imported foods and milk pasteurization facilities while promoting safe food preparation techniques in restaurants and food processing plants. The United States Department of Agriculture (USDA) monitors the health of food animals and the quality of slaughtered and processed meat. The United States Environmental Protection Agency (EPA) regulates and monitors the safety of drinking water supplies.
Parents are advised to call their pediatrician as soon as yersiniosis symptoms appear in a child to prevent the infection from leading to other health problems. The Nemours Foundation offers the following guidelines to parents:
- Never allow a child to eat raw or undercoooked meat
- Give a child only pasteurized milk or milk products
- Wash hands with soap and water before eating and preparing food, before touching infants and after contact with animals or handling raw meat
- Use separate cutting boards for meat and other foods
- Clean all cutting boards, countertops, and utensils with soap and hot water after using them for raw meat. Keep them away from baby bottles and dishwares
- Always cook meat thoroughly, especially pork products
- Dispose of animal feces and sanitize anything it has come into contact with
- Avoid drinking directly from natural water sources such as ponds and mountain streams, especially if there nearby farms where cattle, pigs, or goats are raised
- When caring for a family member who has diarrhea, wash hands thoroughly before touching other people and before handling food
- If a pet dog or cat has diarrhea, wash hands frequently and have them checked by a veterinarian for treatment.
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International Commission on Microbiological Specifications of Foods (ICMSF). Microorganisms in Foods 6: Microbial Ecology of Food Commodities (Microorganisms in Foods). New York, NY: Springer, 2005.
Leon, W. Is Our Food Safe: A Consumer's Guide to Protecting Your Health and the Environment. New York, NY: Three Rivers Press (Crown Publishing Group), 2002.
McDevitt, B. L.Diarrhea. Frederick, MD: PublishAmerica Inc., 2005.
Wilson, C. L., Droby, S. Microbial Food Contamination. Boca Raton, FL: CRC Press, 2000.
Centers for Disease Control and Prevention (CDC). 1600 Clifton Road, NE, Atlanta, GA 30333. 1-800-CDC-INFO (1-800-232-4636) or 404-639-3534.<www.cdc.gov>.
Food and Drug Administration (FDA), Center for Food Safety and Applied Nutrition. 5100 Paint Branch Parkway, College Park, MD 20740-3835. 1-888-SAFEFOOD (1-888-723-3663). <vm.cfsan.fda.gov>.
United States Department of Agriculture (USDA), Food Safety and Inspection Service. Meat and Poultry Hotline: 1-888-MPHotline (1-888-674-6854). <www.fsis.usda.gov>.
U.S. Environmental Protection Agency (EPA). 1200 Pennsylvania Avenue, NW, Washington, DC 20460. 202-272-0167. <www.epa.gov>.
Monique Laberge, Ph.D.