The Washington State Department of Health has been over-reporting negative COVID-19 test results for nearly two months.

The error came from the inclusion of negative antibody test results with negative virus test results. Antibody testing is not for diagnosing COVID-19 but instead for people who think they have already been exposed.

The department acknowledged the mistake Wednesday and said it has included negative antibody tests in their counts since April 21.

The error means the number of residents who have tested negative was inflated by about 13%. Perhaps more importantly, it means the state’s percent positivity rate is higher and has been for nearly two months.

As of June 15, 5.5% of people tested statewide had a positive result under the incorrect reporting methodology. Accounting for the error, however, the state’s percent positivity rate is actually 6.2%, a release from the department says.

The negative testing numbers also affect the risk-assessment dashboard used to determine whether a county advances to the next phase, though the department said it has “not impacted decision-making as it pertains to counties advancing through phases,” a news release said.

“We have addressed the problem and the corrected numbers will be included in this afternoon’s updates,” a Wednesday release from the department said.