A study of the coronavirus or COVID-19 infections that covered nearly everyone in the quarantined north Italian town of Vò found that around 40 percent of the cases showed no symptoms, which suggested that asymptomatic cases are important during the spread of the outbreak.
The study, which was led by a scientist at the Padua University in Italy and Imperial College London, also produced evidence that the mass testing combined with the case isolation and the community lockdowns might stop the local outbreak efficiently.
"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. Vò, which has a population of nearly 3,200, was immediately put into quarantine for 14 days after suffering Italy's 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 percent of Vo's population - or 73 people - were positive. After two weeks, only 29 people were positive.
At both times, around 40 percent 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 Vo's 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.
(With agency inputs)