Overview of Foodborne Disease Outbreaks, 2013

During January 1, 2013 through December 31, 2013, public health departments reported 818 foodborne disease outbreaks; these outbreaks resulted in 13,360 illnesses, 1,062 hospitalizations, and 16 deaths.

• 439 outbreaks were caused by a single, confirmed agent
• The most common causes of outbreaks
  • Norovirus caused 35%
  • Salmonella caused 34%

• 9,359 outbreak-related illnesses were caused by a single, confirmed agent and 965 (10%) resulted in hospitalization
• The most common causes of outbreak-related illnesses
  • Norovirus caused 40%
  • Salmonella caused 38%

Foodborne diseases due to known pathogens are estimated to cause about 9.4 million illnesses each year in the United States. Even though only a small proportion of these illnesses occur as part of a recognized outbreak, the data collected during outbreak investigations provide insights into the pathogens and foods that cause illness. Public health officials, regulatory agencies, and the food industry can use these data to create control strategies along the farm-to-table continuum that target specific pathogens and foods.

The data from this report come from CDC’s Foodborne Disease Outbreak Surveillance System (FDOSS). State, local, and territorial health departments report the results of foodborne disease outbreak investigations to this system, and CDC provides an annual summary of outbreak investigations.

When comparing data between years, it is important to note that changes were made to this surveillance system in 2009, and a new food categorization scheme was implemented in 2011.

The findings in this report have at least three limitations. First, only a small proportion of foodborne illnesses that occur each year are identified as being associated with outbreaks. The extent to which the distribution of food vehicles and locations of preparation implicated in outbreaks reflect the same vehicles and locations as foodborne illnesses not associated with outbreaks is unknown. Similarly, not all outbreaks are identified, investigated, or reported. Second, many outbreaks had an unknown etiology (cause), an unknown food vehicle, or both, and may not be well represented by those outbreaks in which a food vehicle or etiology could be identified. Finally, CDC’s outbreak surveillance system is dynamic. Agencies can submit new reports and change or delete reports as information becomes available. Therefore, the results of this analysis might differ from those in other reports.

Foodborne Outbreak Online Database (FOOD Tool) is a web-based program you can use to search CDC’s Foodborne Disease Outbreak Surveillance System database. FOOD Tool lets users search foodborne disease data by year, state, food and ingredient, location where food was prepared, and cause. It provides information on numbers of illnesses, hospitalizations, deaths, the germ, and the confirmed or suspected cause.

For guidance on using the data and limitations to keep in mind when searching by food or ingredient, take a look at frequently asked questions about FOOD Tool.

Surveillance for Foodborne Disease Outbreaks – United States, 1998-2008 describes 11 years of data about the causes of outbreaks and where they occur; the pathogens and foods that caused the most outbreaks, illnesses, hospitalizations, and deaths; and trends in the pathogens and foods associated with outbreaks over time. Learn more >

Although foodborne disease outbreaks are a nationally notifiable condition, many factors can influence outbreak investigation and reporting, including available resources (such as time, staff, and laboratory capacity), health department priorities, and the characteristics of an outbreak (such as its size and severity).

Even well-conducted investigations may not be able to identify the cause of an outbreak. Several factors influence whether investigators can identify the cause of an outbreak, including the timing of when a specimen is obtained.

• Infections are often diagnosed using specific laboratory tests that can identify bacteria, chemical agents and toxins, parasites, and viruses. When an outbreak isn’t identified until after the optimal time to obtain specimens from ill people, it may not be possible to obtain specimens for laboratory analysis or the laboratory tests may be negative.
• When timely specimens are obtained, other factors can lead to the cause not being detected. For example, clinical laboratories may not have the resources needed to identify some germs. In these outbreaks, the state public health laboratory or CDC may perform additional tests to try to identify the germ.

Even if the cause is not identified, CDC encourages states to report all foodborne disease outbreak investigations.

Even the most thorough investigations can fail to identify the contaminated food under certain circumstances, such as when most of the people who became sick ate many of the same foods (making it hard to identify the one that caused them to become ill), the number of people ill is very small, or the outbreak is identified after people’s memories of what they ate before getting sick have faded. CDC encourages health departments to report all foodborne outbreak investigations. Even if the contaminated food is not determined, we can learn useful information that can help shape prevention efforts.