WEDNESDAY, March 14 (HealthDay News) -- The number of foodborne disease outbreaks in the United States caused by imported food rose in recent years, according to a new federal government study.

Researchers at the U.S. Centers for Disease Control and Prevention reviewed outbreaks reported to the CDC's Foodborne Disease Outbreak Surveillance System between 2005 and 2010. During those five years there were 39 outbreaks and more than 2,300 illnesses linked to imported food from 15 countries.

Of those outbreaks, nearly half (17) occurred in 2009 and 2010.

The most common types of imported food associated with outbreaks were fish (17 outbreaks) and spices (six outbreaks, including five from fresh or dried peppers). Asia was the source of most of the imported food products that caused outbreaks (nearly 45 percent).

The study was scheduled for presentation Wednesday at the International Conference on Emerging Infectious Diseases, in Atlanta.

"It's too early to say if the recent numbers represent a trend, but CDC officials are analyzing information from 2011 and will continue to monitor for these outbreaks in the future," lead author Hannah Gould, an epidemiologist in CDC's division of foodborne, waterborne and environmental diseases, said in a news release from the American Society for Microbiology.

"As our food supply becomes more global, people are eating foods from all over the world, potentially exposing them to germs from all corners of the world, too," Gould noted. "We saw an increased number of outbreaks due to imported foods during recent years, and more types of foods from more countries causing outbreaks."

Between 1998 and 2007, annual U.S. food imports increased from $41 billion to $78 billion, and much of that growth was in fruit and vegetables, seafood and processed food products, according to a report by the Economic Research Service (ERS) of the U.S. Department of Agriculture.

Overall, about 16 percent of all food consumed in the United States is imported, including up to 85 percent of seafood and up to 60 percent of fresh produce, the ERS report said.

Gould said her study likely underestimates the actual number of outbreaks caused by imported food because the origins of many foods that cause outbreaks are not known or not reported.

"We need better -- and more -- information about what foods are causing outbreaks and where those foods are coming from," Gould said. "Knowing more about what is making people sick, will help focus prevention efforts on those foods that pose a higher risk of causing illness."

Research presented at medical meetings should be viewed as preliminary until published in a peer-reviewed journal.

More information

The U.S. Centers for Disease Control and Prevention has more about foodborne illness.