Investigation of a norovirus outbreak at a catered social event, Australian Capital Territory, 2024

Background: An outbreak of gastrointestinal illness was notified, affecting attendees at a private function in the Australian Capital Territory (ACT) in 2024. Investigations were conducted to determine the infectious agent, source of illness and mode of transmission, as well as to determine any public health actions required to prevent further illness. Methods: Function attendees were surveyed using a modified standard gastroenteritis questionnaire. A confirmed outbreak case was defined as an individual who was unwell after attending the event and had a norovirus-positive clinical sample; a probable outbreak case was defined as an individual who was unwell with clinically compatible symptoms after attending the event. A case-control study was conducted to identify food items associated with illness. Food safety inspections were performed, and food samples were tested at the ACT Government Analytical Laboratory. Clinical samples were collected from unwell attendees and from an asymptomatic food handler. Results: There were approximately 250-500 attendees at the function; 224 attendees completed the questionnaire and there were 65 cases (5 confirmed and 60 probable). A food handler who had previously been unwell, and who prepared fruit and meat platters for the function more than 96 hours after their symptoms had resolved, subsequently tested positive for norovirus. Environmental Health investigations showed the venue had good food practices and handwashing; the investigation identified no ongoing risks to the public. Testing of food samples did not detect any bacterial foodborne pathogens. Epidemiological investigations identified consumption of fresh fruit (odds ratio [OR]: 5.3; 95% confidence interval [95% CI]: 2.4-12.6; p < 0.001) and cured meat (OR: 2.7; 95% CI: 1.2-6.2; p = 0.02) as significantly associated with disease. Conclusion: Epidemiological and clinical evidence indicates that norovirus was transmitted via contaminated fresh fruit and cured meat platters. Despite the venue having good food handling and handwashing practices, it was likely due to a food handler who had been unwell in the week prior to the function and prepared the implicated foods more than 96 hours after their symptoms resolved. This outbreak investigation shows that safe food practices and exclusion periods reduce but do not eliminate risk completely. Our findings highlight the need for continued education on effective hand hygiene in food preparation settings, especially following gastrointestinal illness.