What Is a Foodborne Outbreak?

Medically Reviewed by Poonam Sachdev on November 11, 2021

A foodborne outbreak is when two or more people have the same illness after consuming the same food or drink. More than 250 foodborne diseases have been identified.

A foodborne illness, or food poisoning, happens when you fall ill after eating or drinking food that’s contaminated by:

  • Bacteria
  • Toxins
  • Viruses
  • Chemicals
  • Parasites
  • Other agents

There are about 48 million cases of foodborne illnesses in the U.S. every year. Out of these, about 128,000 people are hospitalized and 3,000 people die.

For example, a 2019 outbreak of E. coli infected 167 people in 27 states, with 85 reported hospitalizations. Public health officials traced the outbreak to romaine lettuce grown in the Salinas Valley, California.

A 2020 outbreak of Salmonella Newport was traced to red onions. A total of 1,127 people in 48 states were infected, and there were 167 hospitalizations. 

Anyone can get a foodborne illness, but the people more likely to get sick are:

  • Older adults
  • Pregnant women
  • Young children 
  • People with weakened immune systems 

What Are the Causes of Foodborne Illnesses and Outbreaks?

In the U.S., common causes of foodborne illnesses include: 

Norovirus. About half of all foodborne illness outbreaks are caused by norovirus. Most of these outbreaks happen in places like restaurants.

Salmonella. There are about 1.35 million cases of salmonella a year in the US.

Salmonella outbreaks have been linked to a variety of foods including: 

  • Seafood
  • Onions
  • Deli meats
  • Prepackaged salads

Clostridium perfringens. An estimated 1 million illnesses each year are caused by C. perfringens. The bacteria can be found in the environment, in the intestines of animals, and on raw meat and poultry.

Campylobacter. Campylobacter causes about 1.5 million illnesses a year in the US.You can get infected with campylobacter if you eat raw or undercooked poultry or if you eat something that has touched raw poultry. You can also get it from seafood, other meat, produce, and untreated water.

Staphylococcus aureus (Staph). Staph is a bacteria found on the skin of people and animals. It can also grow and produce toxins in food such as:

  • Fish
  • Processed meats
  • Milk
  • Custard 

How Are Foodborne Outbreaks Stopped?

The aim of a foodborne outbreak investigation is to control the outbreak, prevent more infections, and learn how to prevent future outbreaks.

The steps in foodborne outbreak investigations are:

  1. Detect the outbreak. A foodborne illness outbreak is usually detected using public health data. This data includes formal and informal reports of illnesses. The Centers for Disease Control and Prevention use a national network of laboratories to analyze the DNA of bacteria to detect clusters of foodborne illnesses.
  2. Define and find cases. Public health officials use a list to figure out if a sick person is to be included in an outbreak investigation. They look at lab and surveillance reports, review ER records, and survey people who may have been exposed.
  3. Construct possible explanations (hypotheses). Health officials try to find cases to estimate the severity, possible sources, and timing of the outbreak. They use interviews and questionnaires to determine where and how people got sick.
  4. Test the hypotheses. Health officials gather information to see if sick people are more likely to have eaten a specific food. Food and stool samples may also be tested.
  5. Find the source. The data are studied to find patterns and links between illness and food. Contamination can happen at any point along the food production chain, like during handling, transportation, or processing:
  6. Outbreak control. Once the source is found, authorities will decide what control measures will be taken. These may include:
    1. Recalling food items
    2. Telling consumers to throw away the food or instructing them on how to use it safely
    3. Temporarily closing the eatery or processing plant
    4. Cleaning and disinfecting the facilities
  7. Decide when an outbreak is over. When the number of new cases drops, public health officials may declare the outbreak over. If the number goes up again, they will continue or restart the investigation.

Show Sources

Centers for Disease Control and Prevention: “Burden of Foodborne Illness: Findings,” “Campylobacter (Campylobacteriosis),” “Foodborne Germs and Illnesses,” “Frequently Asked Questions,” “Norovirus,” “Outbreak of E. coli Infections Linked to Romaine Lettuce,” “Prevent Illness From C. perfringens,” “Reports of Selected Salmonella Outbreak Investigations,” “Salmonella,” “Salmonella Infections Linked to Onions,” “Step 2: Define and Find Cases,” “Step 4: Test Hypotheses,” “Step 6: Control an Outbreak,” “Step 7: Decide an Outbreak is Over,” “Steps in a Foodborne Outbreak Investigation.”

Merck Manual: “Staphylococcal Food Poisoning.”

US Food and Drug Administration: “Foodborne Pathogens,” “Outbreaks of Foodborne Illness.”

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