Scientists discovered the presence of SARS-Cov-2 – the virus which causes Covid-19 – in wastewater collected from two northern cities towards the end of 2019.
Italy reported its first known infection in late January.
Giuseppina La Rosa, an expert in environmental wastewater at the Italian National Institute of Health (ISS) who co-led the research, said the findings “may help us understand the beginning of virus circulation” in the country.
The ISS looked at sewage samples collected from wastewater treatment plants in northern Italy between October 2019 and February 2020.
Small studies conducted by scientific teams in the Netherlands, France, Australia and elsewhere have found signs that the virus causing Covid-19 can be detected in sewage.
Many countries are beginning to use wastewater sampling to track the spread of the disease.
Ms La Rosa said the detection of traces of the virus before the end of 2019 was consistent with evidence emerging in other countries about when coronavirus had entered their borders.
Scientists in France have discovered a hospitalised man was infected with the virus as early as 29 December – nearly a month before France confirmed its first cases.
Ms La Rosa said the presence of the virus in the Italian waste samples did not “automatically imply that the main transmission chains that led to the development of the epidemic in our country originated from these very first cases”.
Samples positive for traces of the virus that causes Covid-19 were also found in sewage from Bologna, Milan and Turin in January and February, but all from October and November tested negative.
The institute said it plans to launch a pilot study in July to monitor wastewater at sites identified in tourist resorts.
Northern Italy – where the researchers took their samples from – is where the worst outbreaks took place.
More than 92,500 people have tested positive for the virus in total in the badly-affected northern Lombardy region, which has a death toll of around 16,500.
The whole country has seen a total of 238,159 infections as of Friday, according to official figures.
Meanwhile, more than 34,500 people have died to date.
Additional reporting by Reuters