Here's what likely caused that stomach bug outbreak – and how you can protect yourself

Stomach bug outbreaks were often linked to sick food workers in the two years before the pandemic, a new study finds.

A total of 800 foodborne illness outbreaks occurred between 2017 and 2019, according to the study released Tuesday by the Centers for Disease Control and Prevention.

Of the reported outbreaks with an identified source, sick workers contributed to about 40% of foodborne illness outbreaks, with other causes ranging from improper handling or temperature control. Norovirus – commonly known as the stomach bug – was the most common identified cause of an outbreak, followed by salmonella.

The outbreaks were associated with 875 restaurants and other food establishments across two dozen states.

Proper hand hygiene is important for preventing outbreaks, the authors emphasized – but so is preventing sick food service employees from working.

Most managers surveyed by the researchers said they had a policy restricting sick employees from working. But those protocols, such as notifying a manager when they’re ill or have specific symptoms like vomiting or sore throat with fever, were often incomplete or poorly communicated.

“Although a majority of managers reported their establishment had an ill worker policy, often these policies were missing components intended to reduce foodborne illness risk,” the authors wrote.

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What can help stop outbreaks?

Dr. William Schaffner, medical director at the National Foundation for Infectious Diseases, said the findings should remind of the importance of safe food practices in retail as well as safety net policies for workers.

“Food service establishments need to have mechanisms in place such that ill food service workers are excluded from work,” said Schaffner, who is also an infectious disease professor at Vanderbilt University. “Now, if that's going to happen, we need good medical insurance, and we need policies.”

Policies should ensure food workers have paid sick days, he said.

“I hope this report is a prod, a stimulus, such that the food service industry looks at their policies and procedures that will exclude workers who are ill,” he said.

Elena Naumova, an epidemiologist and data scientist at the Tufts University Friedman School of Nutrition Science and Policy, said better tracking is also needed.

"It is very likely that the number of outbreaks is underreported and only the outbreaks with complete information can be analyzed," she said. "While it improved drastically, there are big gaps in data on food preparation contaminations, food recalls, characteristics of establishments."

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What is norovirus?

Norovirus is the leading cause of foodborne illness in the U.S., causing 58% of foodborne illnesses, according to the CDC. There are roughly 2,500 reported norovirus outbreaks and more than 100,000 hospitalizations each year.

The highly contagious virus causes vomiting, diarrhea, nausea and stomach pain. An outbreak happens when infected people spread the virus to others by handling food, sharing surfaces and caretaking.

While it’s commonly called the stomach flu, it’s not related to the influenza virus.

“This is an extraordinarily transmissible virus," Schaffner said. Even if a person has good hand hygiene, he said, "there's going to be an opportunity for them to transmit the virus," especially in "hectic" work situations like the food industry.

You can get norovirus any time of year, though most U.S. outbreaks happen between November and April, the CDC reports.

While the study was conducted on data prior to the pandemic, Schaffner expects current rates will have returned to previous trends, since lockdowns have ended.

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How can I protect myself?

Children under 5 years old and adults 85 and older are more likely to visit the emergency room from the virus.

The most common places of outbreaks include health care facilities, restaurants, schools and childcare centers, and cruise ships.

Raw leafy greens like lettuce, fresh fruits and shellfish are ingredients commonly associated with a norovirus outbreak. Contamination can also happen during harvest.

You can protect yourself and others from norovirus by:

• Washing your hands often.
• Rinsing fruits and vegetables.
• Staying home and refraining from cooking for others when sick and two days after your symptoms end.

Reach Nada Hassanein at nhassanein@usatoday.com or on Twitter @nhassanein.