(Hillsboro, OR) -- The Washington County Sheriff's Office is warning about a potentially dangerous batch of fentanyl on the streets. Over the last five days, 15 people have overdosed and four people died. Six overdoses and one fatality were in Beaverton, one overdose fatality was in Hillsboro, and four overdoses and two fatalities were in unincorporated parts of Washington County. It's believed all of the cases involved fentanyl.