Nearly 75 people reportedly overdosed on dangerous narcotics, possibly heroin laced with painkiller fentanyl, in Chicago over a three-day span, according to city health and fire officials.

The Chicago Tribune, citing hospital officials, reported by Friday afternoon at least 14 people were rushed to Mount Sinai Hospital in Chicago to be treated for possible heroin overdoses, and some patients still had needles in their arms.

Larry Langford, a spokesman for the Chicago Fire Department, told the Tribune that from Tuesday to Friday, emergency crews had responded to 74 cases.

Diane Hicks, a registered nurse and emergency room director at Mount Sinai, told the Tribune that some of the 14 patients at the hospital had collapsed as soon as they injected themselves with the deadly concoction.

“We suspect what is happening is the same thing that happened in 2006 when people were getting heroin that was cut with fentanyl, which is a very strong narcotic,” she told the newspaper. “That’s what we think is happening.”

The Drug Enforcement Administration and Chicago police are teaming up to try and find the source of the batches.

Chief Mary Sheridan, head of the Fire Department’s emergency medical services division, said all the victims were stabilized with a single dose of Narcan, a heroin antidote carried by paramedics in the city, and then, transported to hospitals. However, fire officials say the victims needed more than one dose of Narcan.

“They’re taking double and triple the doses of Narcan in order to bring them out of their stupor,” Hincks told the newspaper.

Fentanyl-laced heroin has caused overdoes across the nation. The DEA issued a health alert in March.

Fentanyl is used for painful surgical operations, Dr. Steven Aks, chief toxicologist at Stronger Hospital, told the Tribune. The power painkiller adds a potent kick to heroin, making it attractive to buyers seeking better edge.

The last major outbreak of fentanyl-related deaths took place between 2005 and 2007. The outbreak killed more than 1,000 people across the country and dozens specifically in Chicago.