317 Sick After Thanksgiving: A Norovirus Outbreak Traced to a Restaurant’s Salad

On November 26, 2022, the Tazewell County Health Department in Illinois alerted the state health department to a large outbreak of stomach illness linked to one restaurant, "restaurant A." A case-control study identified 317 norovirus infections among people who had eaten there between November 19 and 26 — Thanksgiving week. Megan N. Hanley and Angie Phillips of the county health department and Shana M. Altman of the Illinois Department of Public Health reported the investigation.

Finding the sick

• Probable case: diarrhea (three or more loose stools in 24 hours) or vomiting in someone who ate at the restaurant November 19–26.
• Confirmed case: a probable case with norovirus RNA found in a stool sample.

The county and the restaurant asked diners to come forward. On November 28 news outlets spread the word too, and the number of people reporting illness doubled.

Some people caught it from restaurant patrons in their homes; those secondary cases were not counted in the 317.

Cases by date of illness onset. Credit: CDC, MMWR.

The salad

Diners who ate salad were far more likely to get sick (odds ratio 9.23): 227 of 268 ill people had eaten it, compared with 15 of 40 healthy diners. Twenty-seven sick people who skipped the salad had eaten other sauces and dressings.

Contamination happened during preparation, including when salad, toppings and dressings were portioned out and refrigerated for the next day. The main contributor was likely a food handler who vomited on November 22 and worked November 21–23, preparing food with bare hands.

The response

The restaurant closed voluntarily on November 26 for disinfection and reopened November 29 after a health inspection. The county health department trained food handlers on handwashing, staying home when sick with diarrhea or vomiting, and cleaning.

Because so many people ate at the restaurant over the holiday, investigators could not count every sick and healthy diner, and the true number of cases is probably higher.

Preventing the next one

Norovirus is a leading cause of foodborne outbreaks in restaurants, usually spread by infected workers during food preparation. The FDA's 2022 Food Code names it the leading cause of foodborne illness in the United States. Prevention depends on:

• proper handwashing;
• thorough environmental cleaning;
• appropriate protective equipment, such as gloves;
• keeping workers home while they have vomiting or diarrhea and for at least 48 hours after symptoms end.

Sources

Based on Hanley MN, Altman SM, Phillips A, "Notes from the Field: Outbreak of Norovirus Linked to a Food Establishment — Illinois, November 2022," MMWR, Centers for Disease Control and Prevention; in the public domain.