The FDA has closed an investigation of an outbreak of infections from Listeria monocytogenes without being able to identify a source.

The Centers for Disease Control and Prevention had not posted any information on the outbreak as of Wednesday afternoon.

The outbreak sickened at least 20 people, but the updat from the Food and Drug Administration did not include information on how many states were involved.

Investigators from the FDA conducted traceback efforts as well as doing on-site inspections and sample testing, but the agency did not provide any details about what foods or beverages were involved in those efforts. 

The FDA first posted information about the outbreak in it’s weekly outbreak table on Oct. 6. The investigation was managed by the FDA’s Coordinated Outbreak Response and evaluation Network (CORE) team.

The table below shows ongoing outbreak investigations being managed by FDA’s CORE Response Teams. The investigations are in a variety of stages. Some outbreaks have limited information with active investigations ongoing, others may be near completion. The table below has been abbreviated to show only active investigations.

The Food and Drug Administration will issue public health advisories for outbreak investigations that result in “specific, actionable steps for consumers — such as throwing out or avoiding specific foods — to take to protect themselves,” according to the outbreak table page.

Not all recalls and alerts result in an outbreak of foodborne illness. Not all outbreaks result in recalls.

Outbreak investigations that do not result in specific, actionable steps for consumers may or may not conclusively identify a source or reveal any contributing factors, according to CORE’s outbreak table page. If a source(s) and/or contributing factors are identified that could inform future prevention, FDA commits to providing a summary of those findings, according to CORE officials. Click here to visit the FDA page that has a complete list of outbreak investigations and links to outbreak information.