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Investigation and Outcomes

A probable case was defined as the occurrence of diarrhea (three or more loose stools within 24 hours) or vomiting in a person who dined at restaurant A during November 19–26; probable cases with norovirus RNA detected in a stool specimen submitted to the IDPH laboratory were considered confirmed. Notification of the outbreak and requests for information from persons who had dined at restaurant A during November 19–26 were disseminated to the public by TCHD and restaurant A. The press also shared information about the outbreak on November 28, 2022, encouraging all persons who dined at restaurant A to report this to TCHD; after the release of news stories by the press, the number of reported ill persons doubled.

Overall, 317 case-patients (three with confirmed and 314 with probable norovirus infection) and 40 control patients (persons who dined at restaurant A during November 19–26 and did not become ill) were interviewed initially through an online form to identify epidemiologic links and common food exposures. When secondary phone interviews were conducted to confirm the illness onset date, pizza toppings, salad dressings, and condiments consumed, only 268 ill persons and 40 controls participated; the additional 49 ill persons were lost to follow-up. This activity was reviewed by CDC and was conducted consistent with applicable federal law and CDC policy.*

Although the outbreak originated in Tazewell County, ill persons resided in 10 additional Illinois counties and 12 other states; some secondary cases were reported within the households of restaurant patrons and were not included in the total of 317 case-patients. Restaurant patrons shared illness information and menu items consumed, via an online questionnaire and follow-up interview; among the 317 ill persons sharing information through the online questionnaire and phone calls, 268 (85%) participated in the secondary interview; 49 (15%) ill persons were lost to follow-up. Among the 268 interviewed persons with information on illness onset date, symptoms commenced during November 20–28, with 114 (43%) cases occurring on November 24 (Figure). The mean incubation period (interval from dining at restaurant A until symptom onset) was 22 hours (range = 3–45 hours), and the average illness duration was 37 hours (range = 3–96 hours). Nearly one third of cases (32%) occurred in persons aged 20–49 years (range = 6 months–83 years). Signs and symptoms reported by 317 case-patients through the online questionnaire included vomiting (84%), nausea (80%), diarrhea (68%), myalgias (40%), chills (38%), abdominal cramps (26%), and fever (19%). Seven persons were evaluated in an emergency department, and five visited an outpatient health care provider; no hospital admissions or deaths occurred.

Source of original article: Centers for Disease Control and Prevention (CDC) / MMWR (Journal) (
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