COVID-19: data from the ISS flash survey in wastewaters confirm prevalence of the Delta variant in Italy

ISS, September 8th 2021

A flash survey carried out by the Istituto Superiore di Sanità - ISS (Italian National Institute of Health) in the first half of July in wastewaters confirms the prevalence of the Delta variant in Italy. Overall, the flash survey analysed 35 wastewater samples collected between 4 and 12 July 2021 in 14 different Regions/Autonomous Provinces (A.P.). The presence of SARS-CoV-2 was detected in 40.6% of valid samples. In five samples, collected in purifiers in the Provinces of Bologna, Verona, Rome, Trento, and Bolzano, it was possible to obtain amplifications fit-for-purpose to analyse the variants through sequencing.

The low circulation of the virus in the sampling period – that is, the week when the minimum number of infected individuals was reached in Italy – made it possible to characterise a limited number of positive samples. However, the activity made it possible to highlight the presence in wastewaters of the most widespread variants in that period (Delta and Alpha), and to highlight the presence of the Beta variant in a treatment station in the A.P. Bolzano in the absence of a similar signal in integrated surveillance (microbiological and epidemiological). This could be linked to a small cluster or to the presence of asymptomatic subjects or subjects only temporarily present in the area under surveillance.

Typical mutations of the Delta variant (B.1.617.2) were detected in four of the five treatment stations, while mutations associated with the Alpha variant (B.1.1.7) were detected in the fifth station. These results are in line with what has been reported for the corresponding provinces by the integrated surveillance for the sampling period, and confirm the predominance of the Delta variant in the country in July 2021.