A 300 percent increase in HIV infections among heterosexuals is unusual and concerning, say public health officials in King County.

Public Health Seattle-King County reports 27 new cases this year among heterosexuals. New infections normally hover between 7 to 10 new cases a year.

Dr. Matthew Golden, who directs the county HIV/STD program said there are new challenges.

“We have a growing opioid epidemic. And we have a growing epidemic of homelessness. Those two things have combined to create an enlarging very vulnerable population,” Golden said.

Many, but not all of the new diagnoses are in people who are living homeless and exchanging sex. Earlier this year Public Health identified a cluster of 14 cases of HIV in North Seattle. It's triggered a significant response in the normally resource-starved area. Golden said more than 400 people have been tested.

Public Health has also expanded needle exchange and is working with community partners to increase access to clinical care and a drug regime called PReP, which can prevent HIV.