A study of restaurant food handling has uncovered something diners might find hard to stomach — about 12 percent of the restaurant employees interviewed said they had worked while sick with vomiting and diarrhea.

Restaurants with the heaviest workloads, serving more than 300 meals on their busiest days, were the most likely to have sick employees on duty, according to the study, published in the Journal of Food Protection.

With about 20 percent of foodborne illness outbreaks involving pathogens transmitted by food handlers, federal authorities have tried to prevent contamination by encouraging hand washing and keeping ill employees away from work. But according to an account in Food Safety News, of the 491 food workers interviewed by the study’s researchers, 58 said they worked while suffering vomiting and diarrhea during two or more shifts in the previous year.

If anything, the study’s data may understate the number of employees who worked while sick. Those who participated were selected by managers and some of the interviews took place within the hearing range of the managers.

The study tries to explain why food handlers would come to work ill. Among other things, it cites restaurant workload and the lack of policies requiring workers to report their illness. Researchers also interviewed 387 restaurant managers.

Workers in the survey who had paid sick leave were only about half as likely to say they had worked while vomiting and experiencing diarrhea. The researchers said that finding was not statistically significant — but that’s possibly because the study was too small to evaluate the low number of restaurant workers whose employers grant paid sick days.

A report published last year found that 90 percent of restaurant workers did not receive paid sick days.

Policies that encourage workers to tell managers when they are ill “may be cost-effective interventions for restaurants, given restaurants’ substantial financial losses associated with foodborne illness outbreaks,” wrote the study’s 11 co-authors. They included officials from state health departments around the country and the U.S. Centers for Disease Control and Prevention.