Officials suspended testing at Immensa Health Clinic Ltd.’s laboratory in Wolverhampton, central England, following a probe into reports of people getting negative PCR test results after previously testing positive via lateral flow tests, the U.K. Health Security Agency said on Friday in an emailed statement.

NHS Test and Trace estimates that around 43,000 people could have been given incorrect negative PCR results between Sept 9 and Oct 12, mostly in the southwest of England, the agency said. It described it as “an isolated incident attributed to one laboratory” but said all samples were now being redirected to other labs. People affected will be contacted and advised to take another test.

There’s “no evidence of any faults” with the test kits themselves, said Will Welfare, public health incident director at UKHSA. “The public should remain confident in using them and in other laboratory services currently provided.”

Immensa Health Clinic Chief Executive Officer Andrea Riposati said the company is “fully collaborating” with UKHSA.