Scientists in Italy have found traces of the new coronavirus in wastewater collected from Milan and Turin in December 2019 – suggesting COVID-19 was already circulating 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.
“This research may help us understand the beginning of virus circulation in Italy,” said Giuseppina La Rosa, an expert in environmental wastewater at the Italian National Institute of Health who co-led the research.
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.
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.
The first Italian was diagnosed on February 20 in Codogno, south of Milan, prompting the closure of 11 nearby towns before the imposition of a national lockdown on March 10, when Italy became the first European country to do so.
After recording 34,500 deaths to date, Italy is now emerging from lockdown.
Contact tracing has identified five people who were infected in northern Italy in mid-January, but the sewage testing places the arrival of the virus in Italy – possibly due to trade ties with China – at least a month earlier than that.
Wastewater studies have also found early traces of the virus in other nations.
A recent study in Barcelona found traces of the virus were present in mid-January, over a month before the first local cases were diagnosed.
A Paris hospital has re-tested samples taken from a suspected pneumonia patient on December 27, discovering he was suffering from Covid-19 nearly a month before the first confirmed cases.
China first reported the virus to the World Health Organisation on December 31, but recorded a tenfold increase in flu cases in December.
Last week Harvard Medical School reported large increases in traffic at hospitals in Wuhan, China’s epicentre, as early as last autumn, around the time of a spike in internet searches in China for symptoms associated with Covid-19.
According to government data seen by the South China Morning Post, a 55-year-old from the Hubei province could have been the first person to have contracted COVID-19.
However, the scientists stressed that the 55-year-old was not “patient zero”, who scientists expect will help them to trace the source of the virus, generally thought to have jumped to humans from bats.
Chinese authorities have identified at least 266 people who were infected with the deadly disease in 2019, all of whom came under medical surveillance at some point.
Some of the cases were likely backdated after health authorities had tested specimens taken from suspected patients.