Connecticut’s Department of Public Health (DPH) announced on Monday the discovery of dozens of false-positive coronavirus tests, attributing the error to a “flaw” in a testing system.

At least 90 tests, which were run through Thermo Fisher Scientific, have wielded false positives, according to the DPH.

As the Hartford Courant reported:

In the one-month period from June 15 to July 17, the department said, 144 people were given positive results after their specimens were run through a system manufactured by Thermo Fisher Scientific of Waltham, Mass.

Acting DPH Commissioner Dr. Deidre Gifford said the bulk of the “affected tests” stemmed from nursing homes and emphasized that the error applies to a “minority of tests in the state.” Those who have received a positive test, he said, should “absolutely assume that that positive result is correct until such time as they are informed by their provider of any change”:

The Thermo Fisher system’s error was discovered when public health lab director Dr. Jafar Razeq and his team were working to validate pool testing, which is the process of testing a large number of specimens at one time. In order to validate that process, the team had to use specimens that were already known to be positive.

But the validation process also required the team to determine the strength or weakness of the positive specimens, and that information isn’t readily available from the Thermo Fisher system. So Razeq and his team went into the raw data to pull out the information they needed — and discovered that some of the test results weren’t actually positive.

Dr. Razeq called the discovery “alarming.”

“When we started looking at the background information on these specimens, we realized that these specimens should have not been reported as positives,” he said.

After retesting 161 positive samples associated with 144 patients, the team found that only 54 patients actually tested positive for the virus.

“If it had not been for us looking into the pool testing to use some of these previously known positive samples, there were no indications that any of these reported positive results would have been questioned,” Razeq said.

Connecticut has reported 48,055 positive cases of the Chinese coronavirus and 4,406 related deaths. The state’s current travel advisory requires people from “a state that has a new daily positive test rate higher than 10 per 100,000 residents or a state with a 10% or higher positivity rate over a 7-day rolling average” to self-quarantine for 14 days.