Researchers from the U.S. Department of Energy’s Oak Ridge Institute for Science and Education analyzed CDC data on foodborne illness outbreaks. They noticed a trend beginning in the late 1990s.

From 1998 to 2008, roughly one in 25 of all restaurant-related illnesses was a result of guacamole or salsa. This translated into 3.9 percent of all foodborne illness cases and contributes to billions in annual healthcare dollars.

"Salsa and guacamole often contain diced raw produce, including hot peppers, tomatoes and cilantro, each of which has been implicated in past outbreaks," researcher Magdalena Kendall of Oak Ridge said in a press release. "[These foods] are often made in large batches, so even a small amount of contamination can affect many customers."

Eating contaminated food can cause nausea, diarrhea, headache and fever. Foods such as guacamole and salsa have lots of vegetables and lots of possibilities for salmonella or E. coli contamination, which is why safety is a must.

"We want restaurants and anyone preparing fresh salsa and guacamole at home to be aware that these foods containing raw ingredients should be carefully prepared and refrigerated to help prevent illness," Kendall said.

Learn more about foodborne illnesses from the CDC, or visit Reuters for more information.