Multistate Outbreaks

Illustration of a map and a magnifying glass.

CDC typically coordinates investigation of between 17 and 36 possible multistate foodborne illness outbreaks each week. These are mostly caused by Listeria, Salmonella, and Shiga toxin-producing E. coli and are usually detected by PulseNet, CDC’s national laboratory network for detecting foodborne outbreaks. PulseNet compares the DNA fingerprints of bacteria from sick people. When multiple people get sick around the same time from bacteria with the same fingerprint, that indicates a possible outbreak.

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 contaminated food, attending the same event, or shopping at the same grocery store or eating at the same restaurant. Public health officials work together to determine what the source of the outbreak is, such as a contaminated food. If a contaminated food is identified, CDC collaborates with local, state, and federal partners, taking steps to prevent additional illnesses:

Public health officials don’t solve every outbreak. Sometimes, outbreaks end before enough information is gathered to identify the likely source and warn the public. The source may also be identified after the outbreak ends and the food items are no longer available. In these instances, the risk to the public is over and an active outbreak warning is no longer needed.

Even if an urgent warning is not needed, CDC maintains a record of all investigated outbreaks and reports the majority of these outbreaks through the National Outbreak Reporting System (NORS). In addition, investigators often publish outbreak reports in scientific journals after an investigation ends to share lessons learned and improve outbreak detection and response in the future. Public health and regulatory officials continue monitoring an outbreak strain after an outbreak ends by studying the pathogen and looking for any new illness associated with it.

Active Investigations of Possible Multistate Foodborne Outbreaks

The table below shows the number of active investigations of possible multistate Listeria, Salmonella, and Shiga toxin-producing E. coli outbreaks coordinated by CDC and includes links to additional information about those outbreaks with current CDC notices or alerts. Additional details about FDA and USDA-FSIS investigational activities for some of the outbreaks listed in the table are available on their websites.

Last updated May 18, 2022 (updated every Wednesday)

Active Investigations of Possible Multistate Foodborne Outbreaks
Pathogen Number of Active Multistate Investigations Current CDC Investigation Notices or Food Safety Alerts
Listeria monocytogenes 2
  • No current notices
Salmonella 12
Shiga toxin-producing E. coli (STEC) 3
  • No current notices
Listeria monocytogenes

2 active multistate investigations

Current CDC Investigation Notices or Food Safety Alerts

  • No current notices

12 active multistate investigations

Current CDC Investigation Notices or Food Safety Alerts

Shiga toxin-producing E. coli (STEC)

3 active multistate investigations

Current CDC Investigation Notices or Food Safety Alerts

  • No current notices

Questions and Answers

Where can I find information on outbreaks caused by other pathogens?

Information on multistate foodborne outbreaks caused by some other pathogens, which are less frequent, can be found on CDC’s selected multistate outbreak investigations webpage and websites for Campylobacter, Vibrio, Shigella, Cyclospora, and hepatitis A virus (HAV).

How many states and people are involved in these active investigations?

For the multistate investigations that have CDC current outbreak notices or alerts, the states and number of cases involved can be found in the specific outbreak notice. The table includes links to those notices and alerts.

Why don’t you post an outbreak notice about every active investigation?

CDC follows a consistent process for evaluating the need to post outbreak notices for ongoing multistate foodborne disease outbreaks. CDC is most likely to post an outbreak notice to warn consumers about a specific food linked to illness when there is continuing risk to the public. CDC posts health alerts or notices to provide advice about the food. Read more about CDC’s public communication process.

Is there another place to find information about foodborne disease outbreaks?

The National Outbreak Reporting System (NORS) receives reports on local, state, and national foodborne outbreaks reported to CDC. Any multistate foodborne disease outbreak investigation that CDC coordinates is reported through NORS. The NORS Dashboard is a publicly available, online tool that displays a subset of information from its reporting system. To obtain additional NORS data for a scientific study or analysis, contact