food borne

foods or beverages contaminated with disease-causing microorganisms, chemicals, or other harmful substances.

What are the most common foodborne diseases? 

The most commonly recognized foodborne 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% 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 foodborne 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 foodborne 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 foodborne, 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 foodborne 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 foodborne 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.  Every year, people become ill after mistaking poisonous mushrooms for safe species, or after eating poisonous reef fishes. 

What foods are most associated with foodborne illness? 

Raw foods of animal origin are the most likely to be contaminated; that is, raw meat and poultry, raw eggs, unpasteurized milk, and raw shellfish.  Because filter-feeding shellfish strain microbes from the sea over many months, they are particularly likely to be contaminated if there are any pathogens in the seawater.

Foods that mingle the products of many individual animals, such as bulk raw milk, pooled raw eggs, or ground beef, are particularly hazardous because a pathogen present in any one of the animals may contaminate the whole batch.  A single hamburger may contain meat from hundreds of animals.  A single restaurant omelet may contain eggs from hundreds of chickens. 

A glass of raw milk may contain milk from hundreds of cows.   A broiler chicken carcass can be exposed to the drippings and juices of many thousands of other birds that went through the same cold water tank after slaughter. 

Fruits and vegetables consumed raw are a particular concern.  Washing can decrease but not eliminate contamination, so the consumers can do little to protect themselves.  Recently, a number of outbreak have been traced to fresh fruits and vegetables that were processed under less than sanitary conditions. 

These outbreaks show that the quality of the water used for washing and chilling the produce after it is harvested is critical.  Using water that is not clean can contaminate many boxes of produce.  Fresh manure used to fertilize vegetables can also contaminate them. 

Alfalfa sprouts and other raw sprouts pose a particular challenge, as the conditions under which they are sprouted are ideal for growing microbes as well as sprouts, and because they are eaten without further cooking. 

That means that a few bacteria present on the seeds can grow to high numbers of pathogens on the sprouts.   Unpasteurized fruit juice can also be contaminated if there are pathogens in or on the fruit that is used to make it.