Scientists in Italy have found traces of the new coronavirus in wastewater collected in December 2019, suggesting the virus was already in northern Italy before China reported the first cases.
The Italian National Institute of Health looked at 40 sewage samples collected from wastewater treatment plants in northern Italy between October 2019 and February 2020.
An analysis released on Thursday said samples taken in Milan and Turin on December 18 showed the presence of the SARS-Cov-2 virus.
Giuseppina La Rosa, an expert in environmental wastewater at the Italian National Institute of Health who co-led the research, said the information will help understand the beginning of virus circulation in Italy.
A spokeswoman for the institute said the full data and study would be published next week.
Research in the Netherlands, France, Australia and elsewhere has found signs that the virus that causes COVID-19 can be detected in sewage, and many countries are beginning to sample wastewater to track the disease.
Scientists said the detection of traces of the virus before the end of 2019 was consistent with evidence in other countries that COVID-19 may have been circulating before China reported the first cases on December 31.
Noel McCarthy, an expert in population evidence and technologies at Britain's Warwick Medical School, said the detection of SARS-Cov-2 genetic material in Italian wastewater in December was "reliable evidence of cases of COVID-19 being present there at that time".
Rowland Kao, an epidemiology and data professor at Scotland's Edinburgh University, agreed it was plausible the disease could have circulating then, but added, "(This finding) does not on its own, however, tell us if that early detection was the source of the very large epidemic in Italy, or if that was due to a later introduction into the country."
A study in May by French scientists found that a man was infected with COVID-19 as early as December 27, 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 2020. Samples taken in October and November 2019 tested negative.
The institute said it plans to launch a pilot study in July to monitor wastewater in tourist resorts.
Coronavirus has killed more than 34,500 people in Italy, according to Johns Hopkins University.
It also has more than 238,000 cases of the virus.
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