Outbreak investigation of norovirus gastroenteritis in a childcare facility in Central Queensland, Australia: a household level case series analysis

Introduction: Noroviruses are one of the most common causes of gastroenteritis in all age groups, including children. However, little has been reported on the transmission of norovirus within childcare facilities and the subsequent impact at the household level. Methods: We conducted an outbreak investigation of norovirus gastroenteritis in Central Queensland, Australia during May 2021, in a childcare facility and the associated exposed households. Case definitions and outbreak management were employed as per the Communicable Disease Network Australia guidelines for norovirus and suspected viral gastroenteritis. Each case or carer and respective household member was interviewed to determine the date and time of symptom onset, health outcomes, and infector-infectee pairs. We estimated attack rates within the childcare facility and households, and basic reproductive number (R0) for norovirus using time-dependent methods. Results: A total of 41 people developed gastrointestinal symptoms as a result of this outbreak, with 25 cases (61%) acquiring the infection in the centre and 16 cases (39%) occurring at households. Serial intervals were estimated as a mean 2.4 days (standard deviation 1.7 days), with a majority of cases (73%) in children under two years of age within the centre. Three faecal specimens were obtained, all detecting norovirus genotype II. The time-dependent R0 was 1.5 (95% confidence interval [95% CI]: 1.0-2.2). Discussion: The attack rate within the childcare facility was highest amongst children aged less than 2 years, highlighting the risk of infection for this age group. We recommend the exclusion of asymptomatic household contacts from childcare facilities to reduce the length and severity of norovirus outbreaks. Further investigation into childcare facility risk factors and associated households are required to optimise public health interventions.