Food poisoning – diagnosis, causes and prevention

Food poisoning – diagnosis, causes and prevention – includes related article

Summertime thoughts inevitably drift towards picnics and barbecues — events that can easily turn into a nasty bout of food poisoning if the hamburger isn’t well cooked, the coleslaw stands around too long or someone mixes the salad with dirty hands. Although food poisoning outbreaks in schools, hospitals or other institutions are reported to the Canadian Foodborne Diseases Reporting Centre of Health and Welfare Canada, most cases go unrecorded. Food poisoning outbreaks in Canada are mainly due to microorganisms, widespread in water, soil and sewage. Good hygiene, correct refrigeration, proper cooking and careful food handling can decrease their impact but it’s impossible to completely eradicate food contamination. And while undercooked poultry and meat are commonly to blame for food poisoning, recent outbreaks in North America have also been traced to rice dishes, chocolates, low-cal ice cream, garlic-in-oil, grilled onions, roast beef, unpasteurized (raw) milk and baked potatoes.

How to tell if you’ve got food poisoning

While a foodborne illness often causes no more discomfort than a stomach ache and transient diarrhea, it can be severe, even fatal — especially in the elderly, children, pregnant women, diabetics, alcoholics and the immune-deficient. The alerting signs of food poisoning are primarily diarrhea, nausea, perhaps also chills, fever and vomiting. But sometimes the only indication is mild diarrhea. The discomfort may begin within a few hours of consuming the contaminated food or only appear several days later when it’s no longer clearly linked to any particular food and is probably self-diagnosed as stomach flu. The usual treatment for food poisoning is bed rest and plenty of fluids, preferably clear water or flat ginger ale — to settle the stomach. If a foodborne source is suspected, report it to the family physician (it’s a reportable disease in some provinces). Also call the doctor if symptoms are severe and/or if there is a high or persistent fever.

Bacteria a frequent cause

Unlike food contaminated by moulds or yeasts which looks “spoiled,” often smells bad and has an obvious mouldy coating, bacteria-infested food may yield few clues. It can look and taste wholesome or perfectly normal. Even the best of shoppers and cooks can’t tell whether a piece of chicken, a hot dog or a clam harbours unwelcome, disease-causing bacteria. Foods most likely to be contaminated include poultry (chicken, duck, turkey), red meats (pork, lamb, beef) and shellfish.

The main thing to remember in reducing the likelihood of food poisoning is not to let your dinner, snack or sandwich become a hospitable “microclimate” for bacteria. Bacteria multiply best in moist surroundings such as meaty broths, gravies, soups, cooked rice dishes and custards. Most bacteria don’t grow well in conditions that are too salty, too sugary or too acidic. Some don’t survive if food is boiled or dried. The acid in most fruit juices prevents the growth of food-poisoning microbes. Adding enough lemon juice or vinegar to foods can help to curb bacterial reproduction. Many bacteria are killed by cooking at temperatures above 74[degrees]C (165[degrees]F) although their spores may survive heating, germinate and reproduce once favourable conditions return. While many bacteria don’t grow below 0[degree]C, some survive freezing and can multiply if thawed. The chief danger zone for bacterial food contamination ranges from 5[degrees]C – 60 [degrees]C (40[degrees]-140[degrees]F). Foods kept at these temperatures for more than two hours may not be safe to eat.

Some bacterial causes of food poisoning in Canada

* Salmonella, small rod-shaped bacteria that live primarily in sewage, farm fodder and animal intestines, easily contaminate the flesh of meat and poultry. They’re killed by heat and acidic conditions but not by freezing. The major sources of salmonella are raw or undercooked poultry, ham and (less commonly) other meats. Outbreaks have also been documented from chocolates (Belgian chocolates in B.C.), unpasteurized milk (not heated to destroy bacteria), cheese, aircraft meals and even bean sprouts grown in contaminated water (in Britain). According to some estimates, almost three quarters of all broiler chickens are contaminated with salmonella during defeathering, slaughtering and evisceration, when feces splatter the skin. The salmonella also spread easily from raw or undercooked poultry to innocent vegetables, fruit or other foods via contaminated hands, knives, countertops or cutting boards. The eggs of infected chickens can also (rarely in Canada) be infected with salmonella and people should throw out cracked eggs (which allow bacterial proliferation). One public health expert says that “the eggs scare is grossly exaggerated as probably no more than one per 7,000,000 eggs in Canada is salmonella-ridden.”

The symptoms of salmonellosis are abdominal pain, diarrhea, mild fever, chills, headache, nausea and vomiting, developing six to 72 hours — usually 18 to 36 hours, but occasionally as long as seven days — after infection. The discomfort generally lasts a few days. It can be dangerous for the elderly, infants and the immuno-compromised who may become extremely ill.

* Staphylococcus aureus (“staph”) accounts for about one tenth of call Canadian food poisoning cases. Since 20 to 50 per cent of healthy people normally carry these bacteria in their noses, skin and feces, the bacteria are easily transmitted by food handlers. Foods prone to staphylococcal contamination include meats, fish, poultry, ham, custards, cream-filled bakery goods, starchy salads (e.g., pasta or potato salads) and dairy products. Unlike most bacteria, staph can also grow in salty foods such as ham or pickles. Symptoms of staphylococcal foodborne infections are: nausea, vomiting, abdominal pain, headaches and diarrhea (sometimes bloody) — one to eight hours after eating the contaminated item. The symptoms last a day or two; severe illness and death are rare.

* Campylobacter jejuni bacteria may be as common a cause of food poisoning as salmonella but are only a recently recognized source of foodborne illness. In Toronto alone during 1990 there were 640 reported cases and by mid-1991 already 270 cases, representing only a fraction of the Campylobacter illness that really occurs. These corkscrew-like bacteria inhabit the intestines, especially of birds. Campylobacter bacteria are widespread in broiler chickens, also contaminating cattle, pig and lamb carcasses, unpasteurized milk, untreated water, clams and mushrooms. One anecdotal infection route is birds pecking through milk bottle tops (in Britain).

Symptoms of infection resemble those of salmonellosis: severe, sometimes bloody, diarrhea, abdominal cramps and nausea. The illness usually vanishes within a week.

* Clostridium perfringens — sometimes called the “cafeteria germ” — is acquired mainly from restaurant meals. These bacteria, widespread in soil, water and animal intestines, cause food poisoning mainly because of incomplete cooking and inadequate re-warming of cooked meats, casseroles, stews, broths and gravies. The symptoms — diarrhea and cramping abdominal pain — appear eight to 27 hours after ingesting contaminated food, last two to four days and are rarely serious, although the illness can be fatal in infants and the elderly.

* Escherichia coli infections, due to one particularly virulent strain (#0157:H7), sometimes called “hamburger disease” or “BBQ syndrome,” are linked mostly to improperly cooked meat, especially ground beef. First recognized as a cause of foodborne illness in 1982, E. coli outbreaks have since been identified in schools, daycare centres, nursing homes and fast food outlets. (These bacteria killed 17 Ontario nursing home residents in 1985 — picked up from contaminated sandwiches.) Symptoms of gastroenteritis due to E. coli include nausea, vomiting, fever, chills and watery, sometimes bloody, diarrhea. The illness can be very serious and may lead to hemolytic uremic syndrome, kidney failure, occasionally death.

* Bacillus cereus, another common bacterial cause of food poisoning in Canada, causes two types of foodborne illness — a diarrheal and an emetic (vomiting) form. Symptoms are usually mild and clear up fast. The diarrheal type — mainly acquired from soups, meat, poultry dishes and custards — surfaces eight to 16 hours after eating the contaminated food. The emetic form, which comes mainly from Chinese style rice dishes, appears 30 minutes to five hours after eating the contaminated item. Both types vanish quickly.

* Listeria monocytogenes is a recently recognized but rare cause of very serious food poisoning. Listeria bacteria, found in sewage, soil, dust, rivers and animal fodder, often enter food via unwashed vegetables. They can survive at a wide temperature range, from 0[degree]C-45[degrees]C, particularly endangering the very young, the old and pregnant women in whom the illness may cause abortion and stillbirth. When first identified as a deadly type of food poisoning, the illness created “Listeria hysteria.” Media attention peaked when the bacteria were traced to gourmet products, such as Swiss Vacherin cheese. One 1985 California outbreak stemmed from contaminated “Mexican style” soft cheese, resulting in 142 cases and 47 deaths. Several large listeriosis outbreaks have been reported in Europe — one notorious example due to coleslaw made with cabbages grown in soil fertilized by sheep manure. Symptoms of listeriosis range from a mild flu-like illness to life-threatening meningitis (infection of the brain’s outer membranes).

* Clostridium botulinum causes rare but deadly botulism, a paralytic, foodborne illness that affects the nervous system. The botulism bacteria flourish without oxygen and can survive in canned and bottled goods (homemade or commercial). Common sources of botulism are: non-acidic canned or bottled vegetables (such as corn, peas, beans), soil-contaminated foods and prepacked smoked fish. While rare in the U.S. and Canada, botulism is occasionally seen in infants fed unpasteurized honey and has been traced to contaminated Arctic marine products. In Vancouver, 1986 and 1987 outbreaks were linked respectively to garlic-in-oil preparations and restaurant bottled mushrooms. A 1991 Ottawa incident with three serious cases was traced to home-bottled asparagus. Symptoms of botulism are nausea and vomiting, a dry mouth and throat, double vision, problems in speaking and swallowing and, finally, respiratory paralysis and possible death by suffocation. (Administering a botulism antitoxin can reduce the severity of and prevent death from botulism.)

COPYRIGHT 1991 Strategic Inc. Communications Ltd.

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