Summary of Possible Multistate Enteric (Intestinal) Disease Outbreaks

Highlights from the 2021 report

  1. During 2021, CDC investigated 135 possible multistate outbreaks, of which 74 were determined to be outbreaks. Of these, outbreak investigators solved 47 outbreaks (64%). A suspected source was identified for 22 outbreaks and a confirmed source was identified for 25 outbreaks.
  2. Solved multistate outbreaks linked to contaminated food caused 1,740 illnesses, 496 hospitalizations, and 15 deaths. Multistate outbreaks linked to animal contact caused 1,307 illnesses, 329 hospitalizations, and 3 deaths.
  3. Chicken and leafy greens were identified as the source of the most solved foodborne outbreaks (5 each) during 2021. Although root/underground vegetables were the source of just one solved foodborne outbreak, confirmed to be linked to dry bulb onions, the outbreak resulted in the most illnesses associated with solved foodborne outbreaks (1,040) of any food category.
  4. Contact with backyard poultry was identified as the source of both the most solved animal contact outbreaks (12) and the most outbreak-associated illnesses (1,135) of any animal contact category.

Read the full 2021 summary.

Who is this summary for? What can I do with this information?

This is a summary of investigations of possible multistate outbreaks of Salmonella, Shiga toxin-producing E. coli (STEC), and Listeria outbreak infections coordinated by CDC’s Outbreak Response and Prevention Branch, and the foods and animals identified as sources of these outbreaks. A possible multistate outbreak is a group of people with a similar illness living in two or more states. This summary provides information for food, animal husbandry, and pet industries, as well as researchers and the public, about CDC’s multistate investigation process and results. Data from this summary can be used to identify gaps in food safety and animal husbandry practices and inform policies and practices to prevent similar outbreaks from happening again.

Why does CDC investigate enteric disease outbreaks?

Each year in the United States, Salmonella, STEC, and Listeria cause an estimated 1.49 million illnesses, 28,000 hospitalizations, and 700 deaths, at an estimated cost of more than $6 billion. These three germs are the leading causes of multistate foodborne outbreaks.

CDC coordinates a national network of local, state, and federal public health agencies that investigate multistate outbreaks caused by Salmonella, STEC, Listeria, and other bacterial enteric infections to identify the source of the outbreaks and to control them. Responding to outbreaks quickly and effectively can prevent others from getting sick and save lives. Lessons learned during outbreak investigations about contamination sources, modes of transmission, and risk factors for infection provide information to prevent future outbreaks, illnesses, and deaths.

What is CDC’s role in investigating multistate foodborne and animal contact outbreaks?

CDC helps enable rapid and coordinated responses to multistate outbreaks by working closely with state and local health officials, the U.S. Food and Drug Administration (FDA), and the U.S. Department of Agriculture (USDA), including both the Food Safety and Inspection Service (FSIS) and Animal and Plant Health Inspection Service (APHIS).

CDC has a primary role in detecting possible multistate outbreaks through PulseNet, determining which possible outbreaks to investigate, coordinating collection of information on food and animal exposures with state and local partners, analyzing data to determine possible sources of the outbreak, and providing information to assist state and federal agencies in performing pathogen testing and traceback to confirm an outbreak source. When investigators find the source of a multistate outbreak, CDC also works to inform the public and industry about actions that can prevent additional illnesses.

Read more about CDC’s role in investigating multistate outbreaks.

What is CDC’s multistate outbreak investigation process?

CDC is typically coordinating between 17 and 36 possible multistate outbreak investigations each week. These outbreaks are usually detected by PulseNet, CDC’s national laboratory network for detecting bacterial enteric (intestinal) disease outbreaks. PulseNet compares the DNA fingerprints of bacteria from sick people. In 2019, PulseNet transitioned to using whole genome sequencing (WGS) to generate DNA fingerprints for detection of possible outbreaks of Salmonella and STEC. Switching to WGS for these pathogens allows investigators to identify more outbreaks, detect and solve smaller outbreaks, and stop ongoing illnesses.

When multiple people get sick around the same time from bacteria with the same DNA fingerprint, that indicates a possible outbreak. Local and state health officials interview sick people and share that information with CDC. A possible outbreak is determined to be an outbreak if public health officials find something in common linking the illnesses to each other, such as eating the same food, having contact with the same type of animal, shopping at the same grocery store, or attending the same event. Investigators use three types of data (epidemiologic, traceback, and laboratory data) to identify the source of an outbreak. A source of a multistate outbreak is considered suspected if there is only epidemiologic data to support it.  A multistate outbreak source is considered confirmed if it has epidemiologic and at least one other type of data to support it as the source. Multistate outbreaks with either a confirmed or suspected source are considered solved.

Read more about steps in CDC’s investigation process, using data to link outbreaks to a source, and active outbreaks that CDC is investigating.

Previous Summaries