Sweden's Public Health Agency said a faulty test kit had returned some 3,700 false positive results, an error discovered by two laboratories during routine quality controls, according to AFP.

The agency said the PCR kits, which test for an ongoing Covid-19 infection, were made in China by the company BGI Genomics and had been distributed worldwide.

In Sweden, the kits were used by people conducting at-home tests between March and August, the agency said. Mostly, “people who had mild symptoms or who didn't feel any symptoms at the time of the test received false positive results,” the agency said in a statement.

It added that it would contact those affected this week, as well as adjusting Sweden's official number of cases.