Focolaio di COVID-19 in un campo estivo nella Regione Piemonte (2021): descrizione, lezioni apprese e raccomandazioni per futuri campi estivi

COVID-19 outbreak at a summer camp in Piedimont region in 2021: description, lessons learned and recommendations for future summer camps Introduction In August 2021, an outbreak of coronavirus disease 2019 (COVID-19) occurred in a summer camp in Piedmont region, Italy, affecting primarily campers aged ≤16 years. We conducted a retrospective cohort study among campers and personnel (attendees) to determine the attack rate (AR), evaluate possible factors associated with transmission and propose recommended measures for the organization of future summer camps. Materials and methods A de-identified database including demographic, role of attendees, cohorting, means of transportation to the camp, inter-camper interactions, SARS-CoV-2 testing results and symptomatology was used. All analysis data came from a collection of data carried out by the organizing private company and the information related to the mitigation protocol put in place was provided by the health care personnel. All campers were asked to have an antigen/molecular test within 72 hours before departure. Nine dedicated buses departed from different Italian regions towards the camp. All travellers wore a surgical mask during the trip. Upon arrival, regardless of the bus used, the campers were divided into 11 subgroups with no further contact between them unless they were blood relatives. No SARS-CoV-2 screening tests were scheduled for campers after arrival and during the camp period. On the other hand, personnel had a screening test at each shift change. During the camp period, antigen tests were performed at cases with symptoms suggestive of infection. Only attendees enrolled in the private company and those who received at least one test since arrival at the camp were considered in the study. We calculated overall AR and relative risk (RR) along with specific, transmission-focused risk factors. Results Among the 187 study participants, the median age was 14 years (range: 6-45). Seven days after arrival at the camp, 8 campers developed symptoms and tested positive. The overall AR was 33.7% (63 out of 187), and 34.2% (50/146) for campers and 31.7% (13/41) for staff, respectively. Among those with available symptoms information, 72% (36/50) were asymptomatic at the time of testing. Only 17.1% of campers had direct contact with blood relatives from other subgroups. The AR of participants using a bus was 36.2% (59/163) with an RR of 1.18 (95% CI = 0.51-2.73,) and the AR of those belonging to a subgroup was 35% (62/177) with an RR of 3.5 (95% CI = 0.54-22.7). For personnel, participation to a subgroup gave an AR of 38.7% (12/31) and an RR of 3.87 (95% CI = 0.57-26.18). All but four subgroups had a high AR (>33,3). Conclusions Getting tested prior to traveling and campers separation into low-contact subgroups was not sufficient enough to avoid a high number of infections in this summer camp. Analysis did not allow the identification of an index case or helped to understand whether the outbreak originated from the attendees who travelled on the same bus. The high AR observed in all subgroups suggest that there was frequent contact between attendees belonging to different subgroups. Sharing of common areas such as the canteen and contact between attendees are possible factors that have contributed to the spread of the outbreak. The experience gained by the analysis of this data was used for the review of measures for the organization of summer camps in 2022.