AMSTERDAM (Reuters) - Dutch health authorities have begun a major project testing blood donation samples to see how many people in the Netherlands may have already had the new coronavirus, often with symptoms so mild they hardly noticed.

The project is being carried out on 10,000 blood donation samples a week by blood bank Sanquin, in cooperation with the country’s National Institute for Health (RIVM).

“It’s possible that you had coronavirus without being sick,” Sanquin spokesman Merlijn van Hasselt told national broadcaster NOS. “If we test for antibodies, we can see whether you’ve already had it ... and over time get a picture of how that’s evolving.”

So far there have been 2,051 cases in the Netherlands of COVID-19, the disease caused by coronavirus confirmed by active testing, and 58 deaths.

However, RIVM spokesman Harald Wychgel said that there is vast uncertainty as to how many people may have already had the virus and have beaten the disease, which the blood tests would show.

Active tests for coronavirus among healthcare workers with cold symptoms at hospitals in the province of Noord Brabant on March 6-8 showed a surprising 3.9% of them had the virus.

However random active testing of patients with flu symptoms in other parts of the country, ongoing since early February, have so far uncovered just a handful of patients, Wychgel said.

“We just don’t know how many people are infected with mild symptoms,” Wychgel said. “There’s a lot of uncertainty around this.”