Investigation of a Norovirus GII.4Sydney[P16] outbreak in a care facility in Portugal, 2022

Abstract Background On the 29th of April 2022 the local Public Health unit was notified of 12 cases of acute gastroenteritis in residents of a long-term care facility (LTCF). A joint epidemiological investigation team was established and initiated an outbreak investigation to characterize the outbreak and implement infection control measures. Methods Epidemiological questionnaires were administered to staff (n = 44) and residents (n = 60). Case definition was LTCF residents or staff members with at least one of the following symptoms: diarrhoea, vomiting, nausea, between April 25th and May 14th, 2022. Stool or vomit samples were collected for 11 individuals. To assess environmental contamination fifteen food samples from previous meals and six surface samples from toilet faucets, wash tubs, and cutting boards were collected. Spatial distribution of cases within the LTCF was performed to guide infection control implementation. Results A total of 43 people met the case definition. Attack rates in residents and staff were 37% (23/63) and 42% (20/48), respectively. Of the total tested specimens, six (6/8) from residents and two (2/3) from staff were positive for the Norovirus (NoV) GII.4 Sydney [P16] variant by genotyping. Two (2/6) samples from surface swabs from the toilet faucet in the resident’s living room were also positive for NoV GII. Food samples were negative for major bacterial agents implicated in gastrointestinal outbreaks. Cases were distributed throughout the LTCF wards with no clear clustering. Four residents required hospital admission. Conclusions Results suggest person-to-person as well as environmental transmission of NoV. Identification of behavioural and spatial patterns of residents and staff and subsequent enactment of infection control strategies mitigated the outbreak. These findings reinforce the need for public health to maintain continuous technical support to LTCF on the implementation of infection control best practices. Key messages • Outbreak investigation in LTCF confirms Norovirus transmission, emphasizing the importance of infection control measures in long-term care facilities. • Study reveals Norovirus outbreak in LTCF, underscores the role of person-to-person and environmental transmission, highlighting the need for robust infection control protocols.