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According to the Food Code, food-borne illness in the United States is a major cause of personal distress and preventable death and is an avoidable economic burden. The Council for Agricultural Science and Technology estimated 6.5 to 33 million people become ill from microorganisms in food, resulting in as many as 9,000 needless deaths every year. The Centers for Disease Control and Prevention (CDC) have consistently stated that where reported, food-borne outbreaks were caused by mishandling of food; most of the time the mishandling occurred within the retail segment of the food industry where ready-to-eat food is prepared and provided to the public for consumption.

Because many foods are agricultural products and have started their journey to your door as animals and plants, raised in the environment, they may contain microscopic organisms. Many foods contain nutrients that make them a place where microorganisms can live and even grow. Some of these organisms are pathogens, which means that under the right conditions and in the right numbers, they can make someone who eats them ill. Raw animal foods such as meat, poultry, fish and eggs often carry bacteria, viruses or parasites that can be harmful to humans.

Because foods are from the environment, they can contain objects such as stones that could cause injury. Food may be contaminated naturally, for example, from the soil in which it is grown or because of harvest, storage or transportation practices. Some foods undergo further processing and at times, despite best efforts, become contaminated. These inherent hazards, along with the hazards that may occur in your establishment, such as metal fragments from grinding, can lead to injury, illness or death.

Food-borne illness is caused by eating contaminated food. A food-borne disease outbreak occurs when two or more people experience similar symptoms from eating the same food. There are many foods that can be culprits in a food-borne illness outbreak or occurrence. Some of the ones we are most familiar with are hamburgers, hot dogs, luncheon meats, chicken and oysters, but other foods can also harbor bacteria. Strawberries, green onions, ice cream and dry cereal can also cause food-borne illness if not properly processed and handled.

Food can be contaminated whether it is made from scratch or prepackaged. However, the main culprit of contamination is bacteria. It is estimated that bacteria is responsible for 90 percent of food contamination, viruses cause approximately 6 percent, chemicals are responsible for 3 percent, and parasites cause approximately 1 percent.

Anyone can fall a victim to food-borne illness, but some members of the population are more susceptible than others. These include pregnant women, the elderly, the very young, and people with impaired immune systems due to AIDS, cancer, diabetes or medications that suppress their immune function. Whereas the general population may recover from an incident in a few days, people in this group are much more likely to die from a food-borne illness.

The main symptoms of food-borne illness are:

• Headache

• Abdominal pain

• Diarrhea

• Fatigue

• Fever

• Vomiting

• Nausea

• Dehydration

Food-borne illnesses are generally classified as food-borne infections, intoxication or toxin-mediated infection. Infections are caused by eating food that contain living disease-causing organisms. Intoxication is caused by eating food that contains a harmful toxin or chemical produced by bacteria or another source, and toxin-mediated infection is caused by eating a food that contains harmful organisms that will produce a toxin once it has been consumed.

A food-borne hazard is a biological, chemical or physical hazard that can cause illness when it is consumed in food.

Food hazards include biological concerns such as:

• Bacterial, parasitic or viral contamination

• Bacterial growth

• Bacterial, parasitic or viral survival

• Bacterial toxin production

• Bacterial, parasitic or viral cross-contamination

Physical objects:

• Stones

• Glass

• Metal fragments

• Packaging materials

Chemical contamination:

• Nonfood-grade lubricants

• Cleaning compounds

• Food additives

• Insecticides

More information can be found on the FDA’s Web site at www.cfsan.fda.gov/~mow/intro.html.

BACTERIA

Bacteria is everywhere: in the air, in all areas of the restaurant and all over one’s body. Most bacteria is microscopic and of no harm to people. Many forms of bacteria are actually beneficial, aiding in the production of such things as cheese, bread, butter, alcoholic beverages, etc. Only a small percentage of bacteria will cause food to spoil and can generate a form of food poisoning when consumed.

Bacteria exists in a vegetative state. The vegetative cells grow and reproduce like any other living organism. Some bacteria forms “spores.” The spores help the bacteria survive in less than ideal environments that may not have enough food or the right amount of moisture or ideal temperature. This spore structure allows the bacteria to survive stresses such as cooking, freezing and high-salt environments. In other words, cooking, freezing or curing will not kill these bacteria. The spores themselves are not harmful (except to babies; the spore Clostridium botuinlum, which can be found in honey, can cause infant botulism). However, if the environmental conditions become suitable for bacterial growth, the spore will turn into a vegetative cell, and this cell can multiply and cause illness.

Bacteria need several things in order to reproduce. Many food service managers refer to these items as F-A-T-T-O-M:

Food

Acid

Temperature

Time

Oxygen

Moisture

Food. Most bacteria prefer high-protein or high-carbohydrate foods like meats, poultry, seafood, cooked potatoes and dairy products.

Acid. Most foods have a pH less than 7.0. Very acidic food like limes and lemons normally do not support bacterial growth. While most bacteria prefer a neutral environment, they are capable of growing in foods that have pHs between 4.5 and 9.0.

The quality known as “pH” indicates how acidic or alkaline (basic) a food or other substance is. The pH scale ranges from 0.0 to 14.0—7.0 being exactly neutral. Distilled water, for example, has a neutral pH of 7.0. Bacteria grow best in foods that are neutral or slightly acidic, in the pH range of 4.6 to 7.0. Highly acidic foods, such as vinegar and most fresh fruits, inhibit bacterial growth. Meats and many other foods have an optimal pH for bacterial growth. On the other hand, some foods normally considered hazardous, such as mayonnaise and custard filling, can be safely stored at room temperature if their pH is below 4.6.

Lowering the pH of foods by adding acidic ingredients, such as making sauerkraut from cabbage or pickles from cucumbers, may render them non-potentially hazardous. This is not a foolproof prevention method, however. For example, although commercially prepared mayonnaise has a pH below 4.6, adding mayonnaise to a meat salad will not inhibit bacteria. The moisture in the meat and the meat’s pH are likely to raise the pH of the salad to a point where bacteria can multiply.

ACIDITY VS. ALKALINITY: pH Levels of Some Common Foods
Vinegar	2.2
Lemons	2.2
Cola drinks	2.3
Commercial mayonnaise	3.0
Grapefruit	3.1
Dill pickles	3.2
Orange juice	3.7
Pears	3.9
Tomatoes	4.2
Buttermilk	4.5
Carrots	5.0
White bread	5.1
Tuna	6.0
Green peas	6.0
Potatoes	6.1
Chicken	6.2
Corn	6.3
Steamed rice	6.4
Fresh meat	6.4
Milk	6.6

Temperature. Most disease-causing bacteria grow between the temperatures of 41˚ and 140˚F. This is called the temperature danger zone. Some bacteria like Listeria monocytogenes, a bacteria that is often the culprit in food-borne illness related to processed luncheon meats, can grow at temperatures below 41˚F.

Time. Bacteria only need about four hours to reproduce enough cells to cause a food-borne illness. This time is the total time the food item spends in the temperature danger zone.

Oxygen. There are aerobic bacteria and anaerobic bacteria, and these two types have different oxygen requirements. Aerobic bacteria must have oxygen in order to grow. Anaerobic bacteria, on the other hand, do not. These bacteria grow well in vacuum-packed or canned food items. Anaerobic conditions might also exist in the middle of large, cooked food masses, such as a large stockpot of stew or the middle of a large roast.

Moisture. The amount of water in a food that is available to support bacterial growth is called water activity. It is measured on a scale between 0.0 and 1.0; water activity must be greater than 0.85 to support bacterial growth. Dairy products, meats, fish, shellfish, poultry, egg, cut melons, pasta, steamed rice and sprouts all have water activity levels between 0.85 and 1.0.

Bacterial growth rate depends upon how favorable these six conditions are. Bacteria prefer to ingest moisture-saturated foods, such as meats, dairy products and produce. They will not grow as readily on dry foods such as cereals, sugar or flour.

Bacterial growth has four phases:

1. Lag phase – little or no growth occurs. This phase lasts a few hours at room temperature, but can be increased if foods are kept out of the temperature danger zone.

2. Log phase – bacteria double every 15 to 30 minutes.

3. Stationary phase – number of bacteria remains fixed because the new organisms being produced are equal to the number that are dying.

4. Death phase – bacteria die off rapidly because they lack the items necessary for their survival.

Bacteria will grow most rapidly when the temperature is between 85°F and 100°F. In most cases, the growth rate will slow down drastically if the temperature is hotter or colder than this. Thus, it is vitally important that perishable food items are refrigerated before bacteria have a chance to establish themselves and multiply. Certain bacteria can survive in extreme hot- and cold-temperature ranges. By placing these bacteria in severe temperatures, you will be slowing down their growth rate, but not necessarily killing them.

The greatest problem in controlling bacteria is their rapid reproduction cycle. Approximately every 15 minutes the bacteria count will double under optimal conditions. The more bacteria present, the greater the chance of bacterial infection. This is why food products that must be subjected to conditions favorable to bacteria are done so for the shortest period possible.

An important consideration when handling food products is that bacteria need several hours to adjust to a new environment before they are able to begin rapidly multiplying. Thus, if you had removed a food product from the walk-in refrigerator and had inadvertently introduced bacteria to it, advanced growth would not begin for several hours. If you had immediately placed the item back into the walk-in, the temperature would have killed the bacteria before it became established.

Bacterial forms do not have a means of transportation; they must be introduced to an area by some other vehicle. People are primarily responsible for transporting bacteria to new areas; the body temperature of 98.6°F is perfect for bacterial existence and proliferation.

A person coughing, sneezing or wiping their hands on a counter can introduce bacteria to an area. Bacteria may be transmitted also by insects, air, water and articles onto which they have attached themselves, such as boxes, blades, knives and cutting boards.

Dangerous Forms of Bacteria

An estimated 76 million cases of food-borne disease occur each year in the United States. The great majority of these cases are mild and cause symptoms for only a day or two. The most severe cases tend to occur in the very old, the very young, those who have an illness already that reduces their immune system function, and in healthy people exposed to a very high dose of an organism.

More precautions should be taken by high-risk groups such as:

• Pregnant women, the elderly and those with weakened immune systems are at higher risk for severe infections such as Listeria and should be particularly careful not to consume undercooked animal products. They should avoid soft French-style cheeses, pâtés, uncooked hot dogs and sliced deli meats, which have been sources of Listeria infections. Persons at high risk should also avoid alfalfa sprouts and unpasteurized juices.

• Persons with liver disease are susceptible to infections from a rare but dangerous microbe called Vibrio vulnificus, found in oysters. They should avoid eating raw oysters.

The most commonly recognized food-borne infections are those caused by the bacteria Campylobacter, Salmonella and E. coli O157:H7, and by a group of viruses called calicivirus, also known as the Norwalk and Norwalk-like viruses.

Campylobacter is a bacterial pathogen that causes fever, diarrhea and abdominal cramps. It is the most commonly identified bacterial cause of diarrheal illness in the world. These bacteria live in the intestines of healthy birds, and most raw poultry meat has Campylobacter on it. Eating undercooked chicken or other food that has been contaminated with juices dripping from raw chicken is the most frequent source of this infection.

Salmonella is also a bacterium that is widespread in the intestines of birds, reptiles and mammals. It can spread to humans via a variety of different foods of animal origin. The illness it causes, salmonellosis, typically includes fever, diarrhea and abdominal cramps. In persons with poor underlying health or weakened immune systems, it can invade the bloodstream and cause life-threatening infections.

E. coli O157:H7 is a bacterial pathogen that has a reservoir in cattle and other similar animals. Human illness typically follows consumption of food or water that has been contaminated with microscopic amounts of cow feces. The illness it causes is often a severe and bloody diarrhea and painful abdominal cramps, without much fever. In 3 to 5 percent of cases, a complication called Hemolytic Uremic Syndrome (HUS) can occur several weeks after the initial symptoms. This severe complication includes temporary anemia, profuse bleeding and kidney failure.

Calicivirus or Norwalk-like virus is an extremely common cause of food-borne illness, though it is rarely diagnosed because the laboratory test is not widely available. It causes an acute gastrointestinal illness, usually with more vomiting than diarrhea, that resolves within two days. Unlike many food-borne pathogens that have animal reservoirs, it is believed that Norwalk-like viruses spread primarily from one infected person to another. Infected kitchen workers can contaminate a salad or sandwich as they prepare it if they have the virus on their hands. Infected fishermen have contaminated oysters as they harvested them.

Some common diseases are occasionally food-borne, even though they are usually transmitted by other routes. These include infections caused by Shigella, hepatitis A and the parasites Giardia lamblia and Cryptosporidia. Even strep throats have been transmitted occasionally through food.

In addition to disease caused by direct infection, some food-borne diseases are caused by the presence of a toxin in the food that was produced by a microbe in the food. For example, the bacterium Staphylococcus aureus can grow in some foods and produce a toxin that causes intense vomiting. The rare but deadly disease botulism occurs when the bacterium Clostridium botulinum grows and produces a powerful paralytic toxin in foods. These toxins can produce illness even if the microbes that produced them are no longer there.

Other toxins and poisonous chemicals can cause food-borne illness. People can become ill if a pesticide is inadvertently added to a food or if naturally poisonous substances are used to prepare a meal. People have become ill after mistaking poisonous mushrooms for safe species or after eating poisonous reef fishes.

More information can be found on the FDA’s Web site at www.cfsan.fda.gov/~mow/intro.html.

The following charts list many food-borne illness, symptoms and prevention.

BACTERIA
Illness: Bacillus Cereus Gastroenteritis		Agent: Bacillus cereus
Onset: Diarrhea type: 8–16 hours Vomiting type: 30 minutes–6 hours	Symptoms: Diarrhea type: Abdominal cramps. Vomiting type: Vomiting, diarrhea, abdominal cramps.	Source: Diarrhea type: Meats, milk, vegetables. Vomiting type: Rice, grains, cereal.
Prevention: Properly heat, cool and reheat foods.

Illness: Bacillus Salmonellosis		Agent: Salmonella spp.
Onset: 6–48 hours	Symptoms: Nausea, vomiting, abdominal cramps, headache, fever and diarrhea (may cause dehydration in infants and elderly).	Source: Raw poultry, poultry salads, raw meat, fish, dairy products, eggs, improperly cooked custards and sauces, tofu, sliced melon, sliced tomatoes.
Prevention: Cook poultry to 165˚F for at least 15 seconds, cook other foods to proper minimum internal temperature, avoid cross-contamination, properly cool and refrigerate foods.

Illness: Shigellosis		Agent: Shigella spp.
Onset: 1–7 days	Symptoms: Diarrhea (may be bloody), abdominal pain, fever, nausea, cramps, vomiting, chills, fatigue, dehydration.	Source: Cold salads (tuna, potato, chicken, shrimp), lettuce, raw vegetables, dairy products, poultry.
Prevention: Make sure employees practice good hygiene, avoid cross-contamination, properly cool foods.

Illness: Listeriosis		Agent: Listeria monocytogenes
Onset: 1–3 weeks	Symptoms: Fever and diarrhea. In highly susceptible populations, may cause septicemia, meningitis and encephalitis. In pregnant women, it may result in stillbirth.	Source: Unpasteurized soft cheeses, hot dogs, deli meats, seafood, poultry, meat, raw vegetables.
Prevention: Only use pasteurized dairy products, avoid cross-contamination, wash vegetables, cook food to minimum internal temperatures.

Illness: Staphyococcal Gastroenteritis		Agent: Staphylococcus aureus
Onset: 1–6 hours	Symptoms: Diarrhea, abdominal cramps, nausea, vomiting. In severe cases. May cause headache, changes in blood pressure and pulse, and muscle cramping.	Source: Foods reheated or held improperly, meat, poultry, eggs, dairy products, cream-filled pastries, cold salads.
Prevention: Have employees practice proper hand-washing technique, properly refrigerate and cool foods.

Illness: Clostridium Perfringens Gastroenteritis		Agent: Clostridium perfringens
Onset: 8–22 hours	Symptoms: Diarrhea, nausea, abdominal pain.	Source: Meat, stews, beans.
Prevention: Practice proper time and temperature controls.

Illness: Botulism		Agent: Clostridium botulinum
Onset: 12–36 hours	Symptoms: Fatigue, weakness, vertigo, blurred or double vision, difficulty speaking and swallowing, and dry mouth. Eventually leads to paralysis and death.	Source: Improperly canned foods, untreated oil and garlic mixtures, temperature-abused onions sautéed in butter, leftover baked potatoes, stews, MAP and sous vide foods.
Prevention: Do not serve home-canned products; practice careful time and temperature controls; sauté onions to order; properly cool leftovers.

Illness: Campylobacteriosis		Agent: Campylobacter jejuni
Onset: 2–5 days	Symptoms: Fever, nausea, diarrhea (watery or bloody), abdominal pain, headache and muscle pain.	Source: Poultry, unpasteurized milk, unchlorinated water.
Prevention: Thoroughly cook foods to proper minimum internal temperature, do not use contaminated water sources.

Illness: Hemorrhagic Colitis		Agent: Shiga toxin-producing Escherichia coli (includes O157:H7 and O157:NM)
Onset: 2–72 hours	Symptoms: Diarrhea, severe abdominal cramps and vomiting. May cause kidney failure in the very young.	Source: Undercooked ground beef, unpasteurized apple cider, lettuce, alfalfa sprouts, nonchlorinated water.
Prevention: Thoroughly cook ground beef to 155˚F for at least 15 seconds, use pasteurized dairy and juice products, practice good hygiene, avoid cross-contamination.

Illness: Vibrio Parahaemolyticus Gastroenteritis		Agent: Vibrio parahaemolyticus
Onset: Within 3 days	Symptoms: Diarrhea, nausea, vomiting, abdominal cramps, headache.	Source: Undercooked oysters or raw oysters, raw or partially cooked shellfish.
Prevention: Purchase seafood from approved suppliers, avoid cross-contamination, practice proper time and temperature control.

Illness: Vibrio vulnificus Primary Septicemia		Agent: Vibrio vulnificus
Onset: Within 7 days	Symptoms: Fever, chills, hypertension, nausea, and skin lesions.	Source: Raw or partly cooked oysters.
Prevention: Purchase seafood from approved suppliers, avoid cross-contamination, practice proper time and temperature control.

Illness: Yersiniosis		Agent: Yersinia enterocolitica
Onset: 18–36 hours	Symptoms: Diarrhea. Symptoms may seem like appendicitis.	Source: Tofu, unpasteurized milk, meat, oysters, fish, nonchlorinated water.
Prevention: Use pasteurized milk, avoid cross-contamination, cook foods to required minimum internal temperatures, only use a sanitary water supply.

VIRUSES
Illness: Hepatitis A		Agent: Hepatovirus or Hepatitis A virus
Onset: 10–50 days	Symptoms: Sudden fever, fatigue, loss of appetite, nausea, abdominal pain, jaundice.	Source: Shellfish, salads, deli meats, fruit and fruit juice, milk products, vegetables, water, ice.
Prevention: Make sure employees practice good hygiene, get shellfish from approved sources, avoid cross-contamination, sanitize food-contact surfaces, use sanitary water sources.

Illness: Norovirus Gastroenteritis		Agent: Norovirus
Onset: 24–48 hours	Symptoms: Watery diarrhea with cramps, nausea, mild fever.	Source: Salads and other ready-to-eat foods, sandwiches, bakery items, salad dressing, cake icing, contaminated raspberries, oysters and water.
Prevention: Make sure employees practice good hygiene, use sanitary water.

Illness: Rotavirus Gastroenteritis		Agent: Rotavirus
Onset: 24–72 hours	Symptoms: Diarrhea, abdominal pain, vomiting and mild fever.	Source: Water, ice, ready-to-eat foods like salads.
Prevention: Make sure employees practice good hygiene, avoid cross-contamination, use sanitary water, cook foods to required minimum internal temperature.

PARASITES
Illness: Trichinoisis		Agent: Trichinella spiralis
Onset: 2–28 days	Symptoms: Nausea, diarrhea, vomiting, fever and fatigue.	Source: Raw or undercooked pork products, raw and undercooked wild game.
Prevention: Cook pork and wild meat to required minimum temperature; wash, rinse and sanitize equipment; purchase meats from approved sources; have employees practice good hygiene.

Illness: Yersiniosis		Agent: Yersinia enterocolitica
Onset: 18–36 hours	Symptoms: Diarrhea. Symptoms may seem like appendicitis.	Source: Tofu, unpasteurized milk, meat, oysters, fish, nonchlorinated water.
Prevention: Use pasteurized milk, avoid cross-contamination, cook foods to required minimum internal temperatures, only use a sanitary water supply.

Illness: Anisakiasis		Agent: Anisakis simplex
Onset: 1 hour–2 weeks	Symptoms: Coughing, vomiting, abdominal pain, fever.	Source: Raw or undercooked seafood.
Prevention: Obtain seafood from approved sources, use only sashimi-grade fish that has been properly treated to eliminate parasites. If fish is to be eaten raw, it should be frozen to 44˚F for 7 days.

Illness: Giardiasis		Agent: Giardia duodenalis
Onset: 1–2 weeks	Symptoms: Gas, diarrhea, abdominal cramps, nausea, weight loss, fatigue.	Source: Contaminated water and ice and salads and vegetables washed with contaminated water.
Prevention: Use sanitary water supply, ensure employees are practicing safe hygiene.

Illness: Toxoplasmosis		Agent: Toxoplasma gondii
Onset: 6–10 days	Symptoms: Enlarged lymph nodes in head and neck, severe headaches, sever muscle pain, rash.	Source: Contaminated water, raw or undercooked meat (pork, lamb, wild game and poultry).
Prevention: Cook meats to required minimum temperatures, make sure employees practice good hygiene.

Illness: Intestinal Cryptosporidiosis		Agent: Cryptosporidium parvum
Onset: Within 1 week	Symptoms: Severe watery diarrhea.	Source: Water, salads, raw vegetables, milk, unpasteurized apple cider, ready-to-eat foods.
Prevention: Make sure employees practice good hygiene, wash produce, use sanitary water sources.

Illness: Cyclosporiasis		Agent: Cyclospora cayetanensis
Onset: Within 1 week	Symptoms: Watery, explosive diarrhea, loss of appetite, bloating.	Source: Water, raw produce, fish, raw milk.
Prevention: Make sure employees practice good hygiene, wash produce, use sanitary water sources.

INTOXICATION
Illness: Ciguatoxin		Agent: Ciguatoxin
Onset: 30 minutes–6 hours	Symptoms: Vertigo, nausea, hot/cold flashes, diarrhea, vomiting, shortness of breath.	Source: Marine finfish.
Prevention: Purchase fish from an approved source.

Illness: Scombrotoxin		Agent: Scombrotoxin
Onset: Few minutes to a half hour	Symptoms: Dizziness, facial rash or hives, burning feeling in mouth, shortness of breath, peppery taste in mouth, headache, itching, teary eyes, runny nose.	Source: Tuna, mahi mahi, bluefish, sardines, Swiss cheese, anchovies, mackerel.
Prevention: Purchase fish from an approved source, store fish between 32˚ and 39˚F to prevent growth of histamine-producing bacteria.

INVESTIGATING A Food-borne ILLNESS OUTBREAK

Once an outbreak is strongly suspected, an investigation begins. A search is made for more cases among persons who may have been exposed. The symptoms, time of onset and location of possible cases is determined, and a “case definition” is developed. The outbreak is systematically described by time, place and person. A graph is drawn of the number of people who fell ill on each successive day to show pictorially when it occurred. A map of where the ill people live, work or eat may be helpful to show where it occurred. Calculating the distribution of cases by age and sex shows who is affected. If the causative microbe is not known, samples of stool or blood are collected from ill people and sent to the public health laboratory to make the diagnosis.

To identify the food or other source of the outbreak, the investigators first interview a few persons with the most typical cases about exposures they may have had in the few days before they got sick. In this way, certain potential exposures may be excluded while others that are mentioned repeatedly emerge as possibilities. Combined with other information, such as the likely sources for the specific microbe involved, these hypotheses are then tested in a formal epidemiological investigation. The investigators conduct systematic interviews about a list of possible exposures with the ill persons and with a comparable group of people who are not ill. By comparing how often an exposure is reported by ill people and by well people, investigators can measure the association of the exposure with illness. Using probability statistics, similar to those used to describe coin flips, the probability of no association is directly calculated.

For example, imagine that an outbreak has occurred after a catered event. Initial investigation suggested that hollandaise sauce was eaten by at least some of the attendees, so it is on the list of possible hypotheses. We interview 20 persons who attended the affair, 10 of whom became ill and 10 of whom remained well. Each ill or well person is interviewed about whether or not they ate the hollandaise sauce, as well as various other food items. If half the people ate the sauce, but the sauce was not associated with the illness, then we would expect each person to have a 50/50 chance of reporting that they ate it, regardless of whether they were ill or not. Suppose, however, that we find that all 10 ill people ate the hollandaise sauce, but none of the well persons reported eating hollandaise sauce at the event. This would be very unlikely to occur by chance alone if eating the hollandaise sauce were not somehow related to the risk of illness. In fact, it would be about as unlikely as getting heads ten times in a row by flipping a coin (that is 50 percent multiplied by itself 10 times over or a chance of just under 1 in 1000). So the epidemiologist concludes that eating the hollandaise sauce was very likely to be associated with the risk of illness. Note that the investigator can draw this conclusion even though there is no hollandaise sauce left to test in a laboratory. The association is even stronger if she can show that those who ate second helpings of hollandaise were even more likely to become ill, or that persons who ate leftover hollandaise sauce that went home in doggie bags also became ill.

Once a food item is statistically implicated in this manner, further investigation into its ingredients and preparation and microbiologic culture of leftover ingredients or the food itself (if available) may provide additional information about the nature of contamination. Perhaps the hollandaise sauce was made using raw eggs. The source of the raw eggs can be determined, and it may even be possible to trace them back to the farm and show that chickens on the farm are carrying the same strain of Salmonella in their ovaries. If so, the eggs from that farm can be pasteurized to prevent them from causing other outbreaks.

Some might think that the best investigation method would be just to culture all the leftover foods in the kitchen and conclude that the one that is positive is the one that caused the outbreak. The trouble is that this can be misleading because it happens after the fact. What if the hollandaise sauce is all gone but the spoon that was in the sauce got placed in potato salad that was not served at the function? Now, cultures of the potato salad yield a pathogen, and the unwary tester might call that the source of the outbreak even though the potato salad had nothing to do with it. This means that laboratory testing without epidemiological investigation can lead to the wrong conclusion.

Even without isolating microbes from food, a well-conducted epidemiological investigation can guide immediate efforts to control the outbreak. A strong and consistent statistical association between illness and a particular food item that explains the distribution of the outbreak in time, place and person should be acted upon immediately to stop further illness from occurring.

An outbreak ends when the critical exposure stops. This may happen because all the contaminated food is eaten or recalled, a restaurant is closed, a food processor shuts down or changes its procedures, or an infected food handler is no longer infectious or is no longer working with food. An investigation that clarifies the nature and mechanism of contamination can provide critical information even if the outbreak is over. Understanding the contamination event well enough to prevent it can guide the decision to resume usual operations and lead to more general prevention measures that reduce the risk of similar outbreaks happening elsewhere.

More information can be found on the FDA’s Web site at www.cfsan.fda.gov/~mow/intro.html.

POTENTIALLY DANGEROUS FOODS

Some foods are more prone to supporting the rapid growth of bacteria. These foods are called potentially hazardous food, and special attention is paid to them by the FDA and food service operators when dealing with food safety. These foods generally are high in protein and have a pH above 4.5. Potentially hazardous foods include red meat, dairy products, shellfish, fish, raw eggs and poultry. In their Food Code, the FDA classifies the following as potentially hazardous foods:

• Foods of animal origin.

• Foods of plant origin that are heat treated or have raw seed sprouts.

• Cut melon.

• Garlic and oil mixtures.

Other foods that also are potentially hazardous are cooked potatoes and rice, refried beans and vegetables.

Ready-to-Eat Foods

The FDA Food Code classifies the following items are ready-to-eat:

• Raw fruits and vegetables that are washed.

• Fruits and vegetables that are cooked for hot holding.

• All potentially hazardous foods that are cooked then cooled.

• Bakery items.

• Spices, sugar and seasonings.

• Raw animal foods that are cooked or frozen.

• Thermally processed low-acid foods that are packaged in hermetically sealed containers such as smoked salmon.

• Dry, fermented sausages such as pepperoni and dry cured meats such as proscuitto ham.

These foods can become contaminate if they are not handled properly in the preparation process.

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