A Seattle-area man has contracted HIV while taking PrEP, health officials in the Seattle area are reporting.

The unnamed male patient had been infected with an HIV strain resistant to the two medications in Truvada, the commercial name of the HIV pre-exposure prophylaxis.

His medical-care provider reported it to the Seattle & King County Public Health Department, and he is now getting alternative treatment, with a likelihood he’ll do well long term.

Hundreds of thousands of people take PrEP, 6,500 of them in Washington’s King County, according to the department. His case would be the county’s second such diagnosis.

Related: CDC: We’re not getting PrEP to the men who need it

Dr. Matthew Golden, director of the county department’s STD/HIV program, told Seattle’s KIRO TV that the newly diagnosed man says he took PrEP consistently and had sex only with other men.

“The virus he is infected with is resistant to both the drugs contained in Truvada,” Golden told KIRO. “He may have been infected by a multi-drug-resistant form of HIV, though we don’t know for sure.”

Golden said it’s vary rare, but he mentioned in the KIRO report that the department has identified one prior King County case of PrEP failure with a resistant infection.

On March 9, a presentation at the Conference on Retroviruses and Opportunistic Infections, in Boston, described what appeared to be another case, location not identified, but with unconfirmed monitoring of medication and testing. In 2016, two cases with drug-resistant HIV were presented, and in 2017, a third one did not involve drug-resistant HIV.

Golden, in Seattle, stressed the effectiveness of PrEP. If taken consistently, he said, it reduces the risk of acquiring HIV through sex by 90 to 95 percent, with PrEP-resistant infections still treatable.

“It’s important for people to be aware that PrEP is not 100-percent effective.” he said. “It’s very effective, but not 100 percent.”