PORTLAND, Ore. (KOIN) — Authorities in Washington County say they have responded to 15 drug overdoses in the last five days.

Officials say every case is likely related to fentanyl use and that four of the overdoses were fatal.

According to authorities, six of the overdoses and one of the fatalities were in Beaverton while five overdoses and two of the fatalities were in unincorporated Washington County. There was also one fatality in Hillsboro.

All cases are under investigation by the Westside Interagency Narcotics Team. Officials are warning the public that there may be a batch of fentanyl circulating that is “particularly dangerous.”

The Washington County Sheriff’s office says additional information will be released when appropriate.