Disease Outbreaks Associated with Food Imported into U.S.

A new study published by the CDC on February 15, 2017, reported that between 1996 and 2014, a total of 195 outbreak investigations implicated an imported food, resulting in 10,685 illnesses, 1,017 hospitalizations, and 19 deaths. Outbreaks associated with imported foods represented an increasing proportion of all foodborne disease outbreaks where a food was implicated and reported (1% during 1996–2000 vs. 5% during 2009–2014). The number of outbreaks associated with an imported food increased from an average of 3 per year during 1996–2000 to an average of 18 per year during 2009–2014.


Approximately 19% of food consumed in the United States is imported, including approximately 97% of fish and shellfish, approximately 50% of fresh fruits, and approximately 20% of fresh vegetables. The proportion of food that is imported has increased steadily over the past 20 years due to changing consumer demand for a wider selection of food products and increasing demand for produce items year-round.


The CDC defines a foodborne disease outbreak as the occurrence of more than two people with a similar illness resulting from ingestion of a common food. Local, state, and territorial health departments report foodborne disease outbreaks to the CDC through the Foodborne Disease Outbreak Surveillance System. The information collected for each outbreak includes etiology, meaning the cause, set of causes, or manner of causation of the foodborne disease, (confirmed or suspected on the basis of predefined criteria), and (2) year, month, state, implicated food, and number of illnesses, hospitalizations, and deaths. Information is also collected on where the implicated food originated. During 1973–1997, this information was reported anecdotally in the report’s comments section. During 1998–2008, “contaminated food imported into U.S.” was included as a location where food was prepared. Since 2009, the form has included a variable to indicate whether an implicated food was imported into the United States and the country of origin.


The researchers reviewed outbreak reports to identify outbreaks associated with an imported food from the inception of the surveillance system in 1973 through 2014, the most recent year for which data were available. They obtained additional data for some outbreaks (e.g., country of origin) from the FDA and the U.S. Department of Agriculture Food Safety and Inspection Service.


The most common agents reported in outbreaks associated with imported foods were scombroid toxin, poison produced by the action of spoilage bacteria associated with scombroid fish such as mackerel and tuna, although non-scombroid fish also have been involved in outbreaks, and Salmonella. Most illnesses were associated with Salmonella and Cyclospora, a unicellular parasite spread by the ingestion of food contaminated with feces. Aquatic animals were responsible for 55% of outbreaks and 11% of outbreak-associated illnesses. Produce was responsible for 33% of outbreaks and 84% of outbreak-associated illnesses. Outbreaks attributed to produce had a median of 40 illnesses compared with a median of 3 in outbreaks attributed to aquatic animals. All but one of the outbreaks caused by scombroid toxin was associated with fish. Most of the Salmonella outbreaks (77%) were associated with produce, including fruits (n = 14), seeded vegetables (n = 10), sprouts (n = 6), nuts and seeds (n = 5), spices (n = 4), and herbs (n = 1).


Information was available on the region of origin for 177 (91%) outbreaks. Latin America and the Caribbean was the most common region implicated, followed by Asia. Thirty-one countries were implicated. Mexico was most frequently implicated (42 outbreaks). Other countries associated with more than 10 outbreaks were Indonesia (n = 17) and Canada (n = 11). Implicated fish and shellfish originated from all regions except Europe, but were most commonly imported from Asia (65% of outbreaks associated with fish or shellfish). Implicated produce originated from all regions, but was most commonly imported from Latin America and the Caribbean (64% of outbreaks associated with produce). All but one outbreak associated with dairy products involved products imported from Latin America and the Caribbean.


The number of reported outbreaks associated with imported foods, although small, has increased as an absolute number and in proportion to the total number of outbreaks in which the implicated food was identified and reported. Although many types of imported foods were associated with outbreaks, fish and produce were most common. These findings are consistent with overall trends in food importation.


Many outbreaks, particularly outbreaks involving produce, were associated with foods imported from countries in Latin America and the Caribbean. Because of their proximity, these countries are major sources of perishable items such as fresh fruits and vegetables. Mexico is the leading provider of fruit, nut, and vegetable imports, followed by Chile and Costa Rica.  Mexico is the source of approximately one quarter of the total value of fruit and nut imports and 45%–50% of vegetable imports. Similarly, the report’s finding that many outbreaks were associated with fish from Asia is consistent with data on the sources of fish imports.


One quarter of the outbreaks were multistate, reflecting the wide distribution of many imported foods. Systems like PulseNet have helped to improve detection and investigation of multistate outbreaks, resulting in an increased number of multistate outbreaks. The increasing number of outbreaks involving globally distributed foods underscores the need to strengthen regional and global networks for outbreak detection and information sharing. Newer tools like whole genome sequencing can also help to generate hypothetical transmission networks and in some instances facilitate traceback of foods to their origin. Moreover, new tools that aid visualization of supplier networks facilitate the investigation of outbreaks involving the increasingly complex global economy.


Nearly all of the outbreaks involved foods under FDA jurisdiction. Only a small proportion of FDA-regulated foods are inspected upon entry into the United States. New rules under the Food Safety Modernization Act of 2011, including the Preventive Controls Rule for Human Food, Produce Safety Rule, Foreign Supplier Verification Program, and Accreditation of Third Party Auditors, will help to strengthen the safety of imported foods by granting the FDA enhanced authorities to require that imported foods meet the same safety standards as foods produced domestically.


See the CDC Report


See also Medical Law Perspectives, July 2012 Report: Foodborne Illness: When Grabbing a Bite Can Be Deadly


See the Medical Law Perspectives August 10, 2016, Blog: FDA’s Database Makes Proving Causation in Foodborne Illness Cases Much Easier