Between 2017 and 2019, 40 percent of food poisoning outbreaks with a known cause were linked to people who showed up to work in restaurants while sick, the U.S. Centers for Disease Control and Prevention said in a report released Tuesday.

The report, based on a review of 800 food poisoning incidents and using data from 25 state and local health departments, said paid sick leave and other policies to support sick workers can improve food safety outcomes.

Of the 500 outbreaks in which investigators identified at least one cause, 205 involved workers getting sick, the report said. Other common causes included raw food contamination in 88 cases and ingredient cross-contamination in 68 cases.

In 555 outbreaks, investigators were able to determine what virus, bacteria, toxin, chemical or parasite was responsible. Most of the outbreaks were caused by salmonella or norovirus, the report said.

To combat these outbreaks, “comprehensive sick worker policies may be required,” the report said. It highlighted research showing that expanding paid sick leave reduced the frequency with which food service workers came to work sick, noting that paid sick leave provisions were associated with lower rates of foodborne illness.

Daniel Schneider, a social policy professor at Harvard’s Kennedy School, said the report was “sobering” and highlighted that the U.S. is the only wealthy country without federal paid sick leave.

“A report like this shows its real urgency, not only because it’s in the interests of workers, but because it’s in the public interest,” Professor Schneider said.

Of the 725 managers interviewed by state and local health departments, 665 said their businesses required food workers to tell their supervisors if they were sick, and 620 said sick employees were either restricted or prevented from working. Less than half of managers (316) said their companies offer paid sick leave to employees.

Professor Schneider is the director of the Shift Project, which collects data on people in the retail and food service industries. Workers said they were sick because no one was there to cover them, they felt guilty because their co-workers were understaffed, they couldn’t miss work, or they feared reprisal from management, he said.

“Food service workers face truly impossible trade-offs on things like working sick because food service jobs are so underpaid in our economy,” he said.

To stop workers getting sick at restaurants, catering businesses, and food trucks and carts, businesses may need to better enforce existing policies, such as policies that prohibit workers from getting sick; come up with plans for scheduling restaurant workers when someone calls in sick; and adopt “A Culture of Food Safety Where Sickness Absence Is Not Penalized”.

While the health departments providing outbreak information represent “geographically diverse regions,” the report cautions that its findings may not be representative of all outbreaks in the United States. It also said it was based on information gathered before the coronavirus pandemic and acknowledged evidence that many retail food businesses have since changed at least some of their policies.

The CDC estimates that 48 million people fall ill each year from foodborne illnesses. Of these, 128,000 were hospitalized and 3,000 died.