The study was led by scientists at Italy's Padua University and Imperial College London. The scientists looked at the Italian town of Vò. The town has about 3,200 people. It was put under quarantine for 14 days after having Italy's first COVID-19 death on February 21.
An early, unedited version of the study was published in the scientific journal Nature on Monday.
The scientists said they tested 85.9 percent and 71.5 percent of the population of Vo' at two different times.
In the first part of the study, which was done around the time the town's quarantine started, researchers found 73 people were infected. That is about 2.6 percent of the population. In the second part of the study, which was done after the end of the quarantine, they found 29 people were infected. That is about 1.2 percent of the population.
In both parts of the study, about 40 percent of those who were infected did not have symptoms at the time of testing. They also did not develop symptoms afterwards. In other words, they were asymptomatic.
The study produced evidence that testing along with case isolation and community quarantines can stop local outbreaks quickly. Because all of the coronavirus cases found were quarantined, the researchers said, the disease was not able to spread quickly.
Andrea Crisanti is a professor at Padua. Crisanti was one of the leaders of the project.
"Despite ‘silent' and widespread transmission, the disease can be controlled," Crisanti said. "Testing of all citizens, whether or not they have symptoms, provides a way to...prevent outbreaks getting out of hand."
Crisanti has become well known in Italy for his support of widespread testing. Crisanti said the success of Vo's testing also guided wider public health policy in the Veneto Region, where it had "a tremendous impact on the course of the epidemic" there compared to other regions.
I'm John Russell.