Emma Hitt, PhD

March 16, 2012

March 16, 2012 (Atlanta, Georgia) — The number of foodborne disease outbreaks resulting from imported foods increased during surveillance years 2005 to 2010, according to the US Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia.

L. Hannah Gould, PhD, a senior epidemiologist at the CDC, reported the findings during an oral presentation here at the International Conference on Emerging Infectious Diseases 2012.

According to Dr. Gould and colleagues, about 16% of food consumed in the United States is imported from another country, including nearly 84% of fish and 32% of fruits and nuts.

The researchers reviewed outbreaks linked to imported foods reported to the CDC Foodborne Disease Outbreak Surveillance System from 2005 to 2010.

During the surveillance period, 39 foodborne disease outbreaks were reported in which the implicated food had been imported into the United States. These outbreaks resulted in 2348 illnesses, 434 hospitalizations, and 3 deaths.

"The number of foodborne disease outbreaks related to imported foods is increasing," Dr. Gould told Medscape Medical News. "An earlier study from 1998 to 2004 found 19 (average, 2.7 per year) outbreaks due to imported foods, compared with 39 (average, 6.5 per year) in our analysis from 2005 to 2010," she said.

According to Dr. Gould, even in the period studied, the number of outbreaks increased. During the first half of the study period (2005 to 2007), 16 outbreaks were reported; during the second half (2008 to 2010), 23 outbreaks were reported.

The researchers found that Salmonella infection was the most common cause of outbreaks (34%), followed by histamine fish poisoning (scombroid toxin; 26%).

In addition, in one quarter of the outbreaks, imported foods were linked to illnesses in more than 1 state.

Food imported from Canada and Mexico was linked to 7 outbreaks each; from the Bahamas, Indonesia, Thailand, and Vietnam was linked to 3 outbreaks each; from Honduras and the Philippines was linked to 2 outbreaks each; and from China, Ecuador, Fiji, Guatemala, Japan, and Korea was linked to 1 outbreak each. Two outbreaks were linked to imported food of unknown origin.

The most common foods implicated in these outbreaks were fish (17 outbreaks) and spices (6 outbreaks, 5 caused by fresh or dried peppers). This finding was in contrast to data from 1998 to 2002, when dairy outbreaks were much more commonly reported

"Only 3 outbreaks were reported in which dairy was the implicated food in the current analysis, and all of these occurred in 2005 and 2006," Dr. Gould said.

In 9 of the outbreaks, the implicated source was an ingredient used to make other foods. Ingredients included broccoli powder used to make a snack food, jalapeno peppers, dried pepper, sprouts, and fruit used in shakes.

"Our analysis likely represents the tip of the iceberg with respect to the number of outbreaks due to imported products," Dr. Gould said. "Whether an implicated food is imported or not is not always easily determined during foodborne disease outbreak investigations," she explained.

"Continuing to improve linkages between state and local health departments and regulatory agencies will improve collection and reporting of data on the source of foods implicated in foodborne disease outbreaks," the authors note.

"Because imported foods are widely distributed, outbreaks caused by contaminated imported foods often involve multiple states. Efforts to improve the safety of the food supply should include gathering better data on the origin of implicated food items, including import status," they add.

In an independent comment, Michael Doyle, PhD, director of the Center for Food Safety at the University of Georgia in Griffin, noted that the likely reason for this increase is because the United States is importing more food every year.

"In 2007, the US Food and Drug Administration, which has regulatory oversight of 80% of the food supply, handled about 11 million import entries; in 2011, this number had doubled," he reported.

According to Dr. Doyle, unsanitary production and harvesting practices for fish, seafood, and spices are primary contributing factors in pathogen contamination, such as Salmonella. In addition, raw chicken or swine manure are the primary or sole nutrients for growing tilapia and shrimp in many Southeast Asian countries, which is a likely source of Salmonella.

"For fish and spice production in developing countries, there are often unsanitary conditions that contribute to pathogen contamination," he said. "This problem is only going to increase in the future as the United States continues to import increasingly more food."

The study was not commercially funded. The researchers have disclosed no relevant financial relationships.

International Conference on Emerging Infectious Diseases (ICEID) 2012: Presentation O4. Presented March 13, 2012.

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