ROME, June 19 (Xinhua) -- The new coronavirus had already been circulating in Italy as far back as December 2019, a new study by the National Institute of Health (ISS, in its Italian acronym) has found.

The study focused on wastewater samples collected before the pandemic officially broke out on Feb. 21 in Italy's northern Lombardy region, whose capital is Milan, the ISS said in a statement Thursday.

"Traces of the SARS-CoV-2 virus were present in the wastewater in (the northern cities of) Milan and Turin in December 2019," the statement said.

"The study analyzed 40 samples collected between October 2019 and February 2020," commented Giuseppina La Rosa from the Water Quality and Health Division of the ISS Environment and Health Department.

La Rosa, who led the study, said that researchers compared these 40 samples to 24 control samples collected between September 2018 and June 2019.

"The results, which were confirmed by two different labs using two different methodologies, showed the presence of SARS-CoV-2 RNA in samples collected in Milan and Turin on Dec. 12, 2019, and in (the northern city of) Bologna on Jan. 1, 2020," said La Rosa.