COVID-19: 40% of cases in this Italian town were asymptomatic – World Economic Forum

A study of coronavirus infections that covered almost everyone in the quarantined north Italian town of V found that 40% of cases showed no symptoms - suggesting that asymptomatic cases are important in the spread of the pandemic.

The study, led by a scientist at Italys Padua University and Imperial College London, also produced evidence that mass testing combined with case isolation and community lockdowns can stop local outbreaks swiftly.

Image: REUTERS/Marzio Toniolo REFILE - CORRECTING INFORMATION - RC211H9KA5RC

Despite silent and widespread transmission, the disease can be controlled, said Andrea Crisanti, a professor at Padua and Imperial who co-led the work. Testing of all citizens, whether or not they have symptoms, provides a way to ... prevent outbreaks getting out of hand.

Crisanti has become something of a celebrity in Italy for advocating widespread testing well before it became official World Health Organization guidance.

V, which has a population of nearly 3,200, was immediately put into quarantine for 14 days after suffering Italys first COVID-19 death, on Feb. 21.

During that fortnight, researchers tested most of the population for SARS-CoV-2, the coronavirus that causes COVID-19.

A analysis of the results, published in the journal Nature on Monday, showed that at the start of quarantine, 2.6% of Vos population - or 73 people - were positive. After two weeks, only 29 people were positive.

At both times, around 40% of positive cases showed no symptoms. But because all of the coronavirus cases found - whether symptomatic or not - were quarantined, the researchers said, this helped slow the spread of the disease, effectively suppressing it in a few weeks.

Crisanti said the success of Vos mass testing also guided wider public health policy in the wider Veneto Region, where it had a tremendous impact on the course of the epidemic there compared to other regions.

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COVID-19: 40% of cases in this Italian town were asymptomatic - World Economic Forum