Wastewater monitoring of a community COVID-19 outbreak in a Spanish municipality

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) wastewater surveillance has become an increasingly important tool since the initial moments of the coronavirus disease (COVID-19) pandemic, mainly conducted at a large population scale. However, the large-sized sewersheds may not provide suitable information for monitoring localized outbreaks. After the declaration of a community COVID-19 outbreak in two neighborhoods of Castellón (Spain), SARS-CoV-2 RNA levels were monitored in wastewater samples. Moreover, genomic sequencing was performed. Thirty-three samples were collected in 2020, distributed over three points of the sewage network, two of which were close to the areas where the cases were declared. The third point was located at the inlet of the municipal wastewater treatment plant (WWTP). The samples were analyzed by RT-qPCR, using specific N1 and N2 target regions. The sum of confirmed cases, with the date of symptoms onset within the 3 weeks before each sampling day, was calculated. SARS-CoV-2 RNA was detected on most days in the two sampling points at neighborhood level, and the detection became negative when the number of cases with symptoms onset during the last 21 days in the study areas decreased to 0 or 1 case. The genomic sequencing performed for RNA from wastewater and clinical samples showed the same variant. The detection of SARS-CoV-2 and the subsequent non-detection provided the epidemiologists in charge of controlling the outbreak with useful information to confirm its closure, complementing the clinical and epidemiological data. Our findings illustrate the value of wastewater surveillance for localized outbreaks, especially in situations of low incidence of COVID-19 at the broader community level.