A new study quantifying the hidden toll from coronavirus in the province of Bergamo, at the epicenter of Italy’s epidemic, has found that the number of deaths linked to the virus is double the official tally.

The study by the daily L’Eco di Bergamo with the InTwig data analysis agency puts the number of virus deaths last month at 4,500, compared with the official toll of 2,060, in the province of 1.1 million people.

Mayors have warned that the official numbers fail to take into account the many people dying at home or in rest homes who have never been tested for the virus. Under current policies, only those who arrive at hospitals manifesting strong symptoms are tested.

Lombardy accounts for 40% of Italy’s cases and more than half of its deaths, with Bergamo the hardest-hit province in the heavily populated industrial northern region.

Italy, which as recorded the most deaths of any nation, has extended a strict nationwide lockdown, including a shutdown of at least 60% of heavy industry, until April 13. But authorities caution that any return to normal movement will be a slow process.