The combination of an infected food worker and ready-to-eat items like leafy greens is a gut-wrenching proposition at least once a day, according to researchers who analyzed several years of data from the federal government.

But, more often than not, food workers were the true culprits, rather than fresh fruits and vegetables.

There is an average of one foodborne norovirus outbreak every day, typically involving an infected food worker who handles raw or ready-to-eat items such as leafy vegetables, according to the analysis of eight years of data.

According to the research, an estimated 5.5 million foodborne illnesses annually in the U.S. are attributed to norovirus, making it the leading cause of foodborne disease outbreaks.

Aron Hall, an epidemiologist with the Centers for Disease Control and Prevention, led the research. The findings were published online in September and in the October issue of Emerging Infectious Diseases.

The research showed leafy vegetables, fruits and nuts, and mollusks as the most common sources of foodborne outbreaks of norovirus from 2001-08.

However, the report also states a food handler was specifically implicated as the source of contamination in 53% of the outbreaks.

“Food handler contact with raw and ready-to-eat foods was identified as the most common scenario resulting in foodborne norovirus outbreaks,” the report states.

For norovirus outbreaks linked to one specific food, 33% were linked to leafy greens and 16% were linked to fruits and nuts, which were included in one category in the research.

For norovirus outbreaks with available information, the researchers concluded that the likely point of contamination was preparation or service in 85% of outbreaks and production or processing in 15% of the outbreaks.

The researchers’ goal was to identify areas for potential intervention in the contamination process.

Of norovirus outbreaks involving foods prepared in commercial settings, 62% occurred in restaurants or delicatessens, 11% via a catering service, and 4% at a grocery store. A food handler was identified as the contamination source in 53% of the outbreaks and as a potential source in up to 82%, the researchers reported.