ARLINGTON HEIGHTS, Ill. (AP) — Authorities in suburban Chicago are concerned that an increase in deaths from suspected heroin overdoses may involve tainted batches of the drug making their way out of the city.

A more potent mix of heroin is also suspected in a dramatic rise in overdoses inside Chicago.

The Arlington Heights Daily Herald reports that coroners in DuPage and Kane counties are awaiting toxicology results to see if recent deaths there involved heroin laced with the powerful painkiller fentanyl.

McHenry and Lake County officials are also awaiting test results on a handful of cases.

The Chicago Fire Department said last week it had recorded 74 non-fatal overdoses in just three days.

DuPage Coroner Richard Jorgensen says most of the heroin in the county comes from Chicago’s West Side.