Sewage study finds virus was in Italy last year

A study of the sewage system has thrown up an ‘eye-opening’ clue to why Italy was hit so hard by COVID-19.

Italian President Sergio Mattarella stands silent in front of graves, at the cemetery of Codogno, where Italy's first local case of coronavirus was confirmed in February. Picture: Italian Presidency via AP

Coronavirus was present in Italy in mid-December, two months before the country’s first case was diagnosed, a study of sewage water has found.

Samples taken in Milan and Turin on December 18 contained traces of the virus, Italy’s national health institute, which regularly monitors the water supply for viruses, said.

“If we had found this out sooner it would have been a real eye-opener,” Luca Lucentini, a researcher at the institute, said.

The finding backs up discoveries around the world that the coronavirus was well established before it was identified, helping to explain how it become so widespread.

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.

“After the outbreak we were testing sewage for the virus and realised we could check back in time by analysing old frozen samples we hold on to,” Mr Lucentini said.

“The virus stops being contagious in sewage after around two days and its DNA then remains identifiable for a week or two, but longer if it is frozen.”

Researchers found no traces in samples from November. Samples taken in Bologna on January 29 were also positive.

Residents wearing masks wait to do their shopping outside a supermarket in Codogno, southeast of Milan, in March. Picture: AFP

Lucia Bonadonna, another researcher on the team, said the institute was working with American experts on an algorithm to calculate from the samples how many people were infected in Milan and Turin at the time.

“That will also be useful for the future, as we are now planning continual sewage testing in Italian tourist towns on the Adriatic coast from July 1 ahead of national testing in the autumn to catch a possible second wave,” she said.

Sufferers are thought to shed the virus in their faeces from the moment they are infected, days before they show symptoms, meaning sewage testing could spot outbreaks up to two weeks before doctors.

The Italian team are not the first to use sewage to backdate the arrival of the virus: 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.

Earlier this month Harvard Medical School reported large increases in traffic at hospitals in Wuhan, China’s epicentre, as early as last northern autumn, around the time of a spike in internet searches in China for symptoms associated with COVID-19.

The Times