By Kate Kelland
LONDON (Reuters) – A study of coronavirus infections that covered almost everyone in the quarantined city of Vò in northern Italy 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 from the University of Padua in Italy and Imperial College London, also yielded evidence that mass testing combined with case isolation and community closure can quickly stop local outbreaks.
“Despite the ‘silent’ and widespread transmission, the disease can be controlled,” said Andrea Crisanti, a professor at Padua and Imperial, who co-directed the work. “Testing of all citizens, whether or not they have symptoms, provides a way to … prevent outbreaks from spiraling out of control.”
Crisanti has become something of a celebrity in Italy for advocating widespread testing long before he became the official guide for the World Health Organization.
Vò, which has a population of almost 3,200, was immediately quarantined for 14 days after suffering the first death of COVID-19 in Italy on February 21.
During that fortnight, the researchers analyzed the majority of the population for SARS-CoV-2, the coronavirus that causes COVID-19.
An analysis of the results, published in the journal Nature on Monday, showed that at the start of the quarantine, 2.6% of Vo’s population, or 73 people, were positive. After two weeks, only 29 people were positive.
On both occasions, about 40% of the positive cases showed no symptoms. But because all of the coronavirus cases found, whether symptomatic or not, were quarantined, the researchers said, this helped delay the spread of the disease, effectively suppressing it within a few weeks.
Crisanti said the success of Vo’s mass tests also guided broader public health policy in the Veneto region, where it had “a tremendous impact on the course of the epidemic” compared to other regions.
(Report by Kate Kelland; Kevin Liffey Edition)
