It’s now about one month since Covid-19 began to sweep across Italy. With more than total cases topping 40,000 as of 19 March, it is now the worst-affected country outside of China.

But 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.

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While we believe it is too late to enact this approach in a city such as Milan, where infections are out of control, there could still be time to do this in the UK before the crisis gets even worse: the government could identify and isolate clusters, quarantine everyone affected, trace their recent contacts, and quarantine and isolate them, too – whether they had symptoms or not.

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. It became clear that this was a unique epidemiological setting – and an application was put in to keep the town in lockdown and run a second round of tests after nine days.

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.

We made an interesting finding: at the time the first symptomatic case was diagnosed, a significant proportion of the population, about 3%, had already been infected – yet most of them were completely asymptomatic. Our study established a valuable principle: testing of all citizens, whether or not they have symptoms, provides a way to control this pandemic.

The nature of this crisis means that establishing a structured response like this is key, while widespread testing is crucial in telling an accurate story of how many people are affected, and what the mortality rate of the virus actually is. In Italy, we have struggled with a rampant rise of mortality (the number of casualties divided by the number of infected people), which has reached an apparent value of 8% – far higher than the mortality rate in China and grimly close to that during the 2002-2003 Sars outbreak.

This high rate is misleading, though. After the first few days of the initial outbreak, cases were classed as all of those found to be infected by the virus. Yet since then, only the obviously symptomatic subjects – those needing medical care – have been tested for the virus and thus counted as cases.

The decision to only test those who presented for treatment with symptoms of the virus was taken by major Italian public health experts, apparently in line with World Health Organization (WHO) suggestions. The consequence has been that people who haven’t asked for medical attention have only been tested very occasionally in Italy. Nonetheless, asymptomatic or quasi-symptomatic subjects represent a good 70% of all virus-infected people and, still worse, an unknown, yet impossible to ignore portion of them can transmit the virus to others. Full testing would give us a clearer picture of how many people actually have the virus, and how many pass it on.

If the fact that only those presenting with the virus were being tested was accounted for, the mortality percentage would fall to more “normal” levels. This is shown by the mortality in the Veneto region, which is steadily around 2.5-3%, still high but threefold less than the ones in Lombardy and Emilia-Romagna.

Why this marked difference? Veneto is comparable to the other two northern regions for education, general lifestyle, personal income and age of the population – all factors, particularly the last one, believed to influence Covid-19 mortality. Although a non-homogeneous data collection and other variables could explain the difference, there is one main factor that is likely playing a role. In Veneto, the virus was more actively sought out through testing, a programme that included part of the asymptomatic population. Official numbers speak of roughly eight in every 100 people tested in Veneto, against about half and one-third of that proportion in Lombardy and Emila-Romagna, respectively.

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Unfortunately, it would be near impossible to repeat this model in a large city, due to the number of people who would need to be tested. However, our findings warrant careful consideration by health policymakers in Italy and around the world. They invite researchers to eradicate the virus through extensive testing of both symptomatic individuals and all of their social contacts – including relatives, friends and neighbours. In this way, we catch out the disease before it has the chance to spread – and, most importantly, before the carrier has the chance to unwittingly pass it on to other people.

In the absence of specific therapies or a vaccine, quarantine, distancing and identification of asymptomatic carriers remain the only real measures to control this epidemic. In the UK, authorities could still identify and isolate clusters, and test everyone who has come into contact with those infected. Wisely, though probably belatedly, WHO has just this week recommended what we have found in our research to be the best line of defence: testing, testing, testing.

• 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







