Preliminary results from thousands of blood tests conducted across Italy in the past two months suggest that the number of people exposed to the coronavirus was far higher than the number of infections officially confirmed – 248,419 as of Tuesday.

According to the Ministry of Health, 1.482 million people – the equivalent of 2.5 per cent of the entire population – are believed to have coronavirus antibodies in their blood, which indicates that they have been exposed to the virus and had an immune response, but not whether they’re safe from becoming infected again.

The findings are based on nearly 65,000 blood tests on a cross-section of Italian residents, carried out between May 25 and July 15 by the Italian Red Cross on behalf of the Ministry of Health and national statistics agency ISTAT.

More than a quarter of people found to have antibodies, 27.3 per cent, were asymptomatic, pointing to the risk of the illness being spread by people unaware they were carriers.

“The rate of 2.5 per cent might seem low but it can become problematic if we’re not cautious,” ISTAT president Gian Carlo Blangiardo said as the researchers presented their first results on Monday.

“It means that the probability of encountering someone positive for the virus is 2.5; if I encounter 20 people, there’s a 50 percent chance I’ll come into contact with someone positive.”

The rate was significantly higher in parts of northern Italy, where most of Italy’s coronavirus cases have been recorded.

In Lombardy, the northern region with the biggest number of infections by far, 7.5 per cent of people tested had coronavirus antibodies – three times the national average.

In the worst affected province of Bergamo, the rate was as high as 24 per cent.

The highest regional rates were all in the north of Italy, while they were below the national average almost everywhere in the centre and especially the south.

At the lowest end of the scale, the rate among residents of Sicily and Sardinia was just 0.3 per cent.

The results showed that government containment measures and public caution had helped control the spread of coronavirus in Italy, according to Health Minister Roberto Speranza.

However, Speranza warned Italians to remain on guard.

“Even if we’re out of the storm, we’re not yet at a safe port,” he said.

Having antibodies in your blood does not necessarily mean that you’re immune to coronavirus.

It’s not yet known whether people with antibodies can catch the virus again, or how soon.