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Food and Waterborne Illness

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Also known as: Food Poisoning; Gastroenteritis; Stomach Flu

What are foodborne and waterborne illnesses?

Foodborne and waterborne illnesses are conditions caused by eating or drinking food or water that is contaminated by microorganisms or the toxins they produce. They typically cause gastrointestinal symptoms such as abdominal pain, nausea, vomiting, and diarrhea. There are many non-infectious causes of illness from contaminated food and water, and some microorganisms can lead to infections other than gastrointestinal, but these are beyond the scope of this article and are not covered here.

In the United States, the Centers for Disease Control and Prevention (CDC) estimates that as many as 1 in 6 people get sick each year from consuming contaminated food or beverages. Of those, roughly 128,000 require hospitalization and as many as 3,000 die from complications.

The microorganisms that can contaminate food and water include a wide range of bacteria, viruses, and parasites. Some are found throughout the world while others are regional. Some are very common, others more rare. They may cause symptoms in most people who are exposed to them, or only in those who are most susceptible. Regional strains of bacteria may not cause symptoms in the people who are accustomed to them but may make visitors sick. Though the affected water and food may smell, look, and taste normal, they can cause illness ranging from mild and self-limited to severe.

Foodborne and waterborne illnesses can affect anyone at any time but tend to be the most severe in:

  • The very young and the elderly, who may experience serious dehydration
  • Those with weakened (compromised) immune systems such as those with HIV/AIDS or who have had an organ transplant; in these populations, the conditions may be much more severe and difficult to resolve.
  • Those with chronic diseases such as diabetes, heart disease, lung disease or liver disease
  • Pregnant women – some conditions may harm the developing baby.

These illnesses, commonly called food poisoning, may involve single individuals or may be part of an outbreak. Most cases come directly from what is consumed; infrequently, they may be passed from person to person, especially in confined populations such as may be seen in a daycare, cruise ship, nursing home, or institutional setting.

Outbreaks occur when more than one individual develops symptoms after consuming the same food or drink that is contaminated with the same bacteria or toxin. They can be localized or may occur across several states. Public health and government entities continuously monitor food and water quality and take prompt actions to identify, contain, and correct sources of outbreaks. This job has become more complex as food is imported to the U.S. from many countries and as more people travel worldwide.

When doctors or clinical laboratories recognize that cases of suspected food poisoning may be related, they endeavor to get complete medical histories of the people who are affected and obtain samples, usually stool, to send to public health laboratories for testing. Patients can be helpful in this process by sharing information with their doctors on symptoms, type of diarrhea (watery, bloody), recent travel as well as food recently eaten. Sometimes it is useful to write down what was eaten in the last ten days or so. These details may help provide clues as to the cause of illness.

Often, samples of the suspected source of contamination are also tested. Public health laboratories use a molecular test called pulsed-field gel electrophoresis (PFGE) that "fingerprints" DNA to compare the microorganism isolated from people who are ill and then look for the pathogens in food or water samples. This allows the laboratories to rapidly identify common sources of food or waterborne illness. The results from this testing are entered into a database called PulseNet. The database is used by local and state public health agencies, federal food safety regulatory laboratories, and the CDC to compare DNA fingerprints and quickly identify illnesses that have a common source. If one is identified, steps are taken to contain the source of the contamination and limit spread of the illness.

Food Contamination
Food may become contaminated at any point in its growth, processing, storage, and handling. Examples of contamination sources include:

  • Plants may be contaminated by soil, animal waste fertilizers, or water. If contaminated water is used to water or wash produce such as spinach or lettuce, for instance, then the fresh produce may become contaminated.
  • Animals may be colonized by bacteria that do not make them ill but that can make people sick. Salmonella, for instance, are bacteria that are common in poultry. They can be present even inside intact eggs and can make a person ill if the food is not fully cooked.
  • Intestinal bacteria may contaminate meat, such as beef, during processing. If the beef is then ground, the contamination can spread throughout the hamburger produced and, if the meat is not adequately cooked, it can cause illness.
  • Foods such as raw oysters or alfalfa sprouts may become contaminated while maturing and, when eaten raw, they can make a person sick.
  • Workers in the food industry and people in their own homes who do not use sanitary techniques can spread and transfer contamination. For instance, a cutting board that is used to cut contaminated meat and then used to chop produce without being thoroughly cleaned first can spread contamination to the produce. Also, someone who is sick can pass the illness to others during food preparation.
  • Milk and juices that are unpasteurized can be a source of bacterial foodborne illness. Some bacteria, such as Listeria, can grow even when milk is refrigerated.
  • Food that is left out too long, such as at a picnic, may allow the growth of bacteria.
  • Some bacteria and plants produce toxins that can cause foodborne illness. Examples of these are the muscle-paralyzing botulism caused by the toxin produced by Clostridium botulinum bacteria and the toxin produced by Staphylcoccus aureus. Some toxins are destroyed by cooking, others are not.
  • Other toxins and poisons that can contaminate food, such as pesticides and heavy metals such as mercury and lead, or that occur naturally in foods, such as in poisonous mushrooms, can also cause illness but are outside the scope of this article.

Water Contamination
People get waterborne illnesses primarily by ingesting contaminated water, including treated drinking water, well water, water that is used to irrigate crops, and recreational water such as that found in lakes, rivers, and swimming pools as well as some temperate ocean waters. Even ice cubes or the small amounts of water swallowed during swimming can cause illness. When contaminated water is used for washing food, dishes, or surfaces, the contamination can be spread.

The contaminating microorganisms may naturally live in the environment or may get into the water from animal or human feces. Many parasites are hardy and can live in a dormant stage in soil or water for extended periods of time. Water can also become contaminated during natural disasters, such as hurricanes and earthquakes. Anything that adds wastes, sewage, or other health hazards into the water supply and disrupts the availability of treated drinking water has the potential to make people sick.

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