In a Nature roundup, the following (mid April) draft paper has been highlighted as the main scientific publication on that town/survey:
On the 21st of February 2020 a resident of the municipality of Vo, a small town near Padua, died of pneumonia due to SARS-CoV-2 infection. This was the first COVID-19 death detected in Italy since the emergence of SARS-CoV-2 in the Chinese city of Wuhan, Hubei province. In response, the regional authorities imposed the lockdown of the whole municipality for 14 days. We collected information on the demography, clinical presentation, hospitalization, contact network and presence of SARS-CoV-2 infection in nasopharyngeal swabs for 85.9% and 71.5% of the population of Vo at two consecutive time points. On the first survey, which was conducted around the time the town lockdown started, we found a prevalence of infection of 2.6% (95% confidence interval (CI) 2.1-3.3%). On the second survey, which was conducted at the end of the lockdown, we found a prevalence of 1.2% (95% CI 0.8-1.8%). Notably, 43.2% (95% CI 32.2-54.7%) of the confirmed SARS-CoV-2 infections detected across the two surveys were asymptomatic. The mean serial interval was 6.9 days (95% CI 2.6-13.4). We found no statistically significant difference in the viral load (as measured by genome equivalents inferred from cycle threshold data) of symptomatic versus asymptomatic infections (p-values 0.6 and 0.2 for E and RdRp genes, respectively, Exact Wilcoxon-Mann-Whitney test). Contact tracing of the newly infected cases and transmission chain reconstruction revealed that most new infections in the second survey were infected in the community before the lockdown or from asymptomatic infections living in the same household. This study sheds new light on the frequency of asymptomatic SARS-CoV-2 infection and their infectivity (as measured by the viral load) and provides new insights into its transmission dynamics, the duration of viral load detectability and the efficacy of the implemented control measures.
The 43% asymptomatic is a bit less than what was reported from the Princess, but it overlaps it in the 95% CI 32.2-54.7%.
End or March answer, largely obsolete now, but leaving it for some press coverage:
Also March 20 coverage in the Guardian, which is of course not a science venue, but had even more details than even the BMJ coverage; the "opinion piece" in the Guardian was apparently written by the researchers/epidemiologists involved:
in the last two weeks, a promising pilot study here has produced results that may be instructive for other countries trying to control coronavirus. Beginning on 6 March , along with researchers at the University of Padua and the Red Cross, we tested all residents of Vò, a town of 3,000 inhabitants near Venice – including those who did not have symptoms. This allowed us to quarantine people before they showed signs of infection and stop the further spread of coronavirus. In this way, we eradicated coronavirus in under 14 days. [...]
Our experiment came to be by chance. The Italian authorities had a strong emotional reaction to news of the country’s first death – which was in Vò. The whole town was put into quarantine and every inhabitant was tested. The tests were processed by us at the University of Padua. [...]
In the first round of testing, 89 people tested positive. In the second round, the number had dropped to six, who remained in isolation. In this way, we managed to eradicate coronavirus from Vò, achieving a 100% recovery rate for those previously infected while recording no further cases of transmission.
Strong claims here. They also say/claim that
asymptomatic or quasi-symptomatic subjects represent a good 70% of all virus-infected people
referring to COVID-19.
About the authors, the Guardian notes:
Andrea Crisanti is professor of microbiology at the University of Padua; Antonio Cassone is a former director of the department of infectious diseases at the Italian institute of health.
I guess I now know whose publications to look at (in the future).
There's a longer interview with Crisanti on CBC.ca. An intersting bit:
I want to draw a comparison. If you remember the Diamond Princess. They started with few cases. They did the tests only to those [who] were symptomatic. So you develop a symptom, you test positive, you were taken out of the ship.
But day by day, cases, if you remember, they increased up to more than 700. So in this way, they couldn't stop the disease. That couldn't stop the disease in spite of the fact that they were isolated, they were kind of quarantined. And the reason why they couldn't stop it is because the ship was full of asymptomatic people that [were] spreading the virus.
Q: [When you started this in February], the protocol was that you tested people only if they … were returning from a foreign place, or from China, or if they had symptoms. ... You ignored that and went to everybody.
Yeah, we ignored that because we weren't convinced that the disease was transmitted only by symptomatic individuals. We found this quite implausible. And so this is the reason why we tested everybody.