An isolated drug overdose is believed to have killed three people and hospitalized four others in Pittsburgh, sparking concern over an unrelated "tainted, potentially deadly batch of drugs in the community," authorities said.

Police responded to what they called a “medical situation” early Sunday and found the seven victims – all wearing orange wristbands – in the South Side Works area of the city, the Pittsburgh Public Safety Department said.

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The victims appeared to have been at the same venue together before going to an apartment where they all took narcotics, police said. It wasn't immediately clear what specific drug was ingested.

Five victims were found in an apartment, police said. One was found in an elevator outside the apartment and another was discovered on a street corner at 26th and Carson.

Four of the surviving victims ranged from serious to critical condition when they were rushed to Mercy Hospital, police said. Three of the victims have since been upgraded to stable condition while one remains critical, the Pittsburgh Post-Gazette reported

There were no initial signs of drug paraphernalia or needles on the victims, who were all male, police told WPXI-TV.

Police noted that the incident appeared isolated and was not a case of a tainted drug distributed on a large scale. People who attended events where orange wristbands were given have no cause for concern, police said.

However, police went on to urge the public against using drugs over concern of a tainted and potentially deadly batch in the community. "Simply put: You do not know what's in that drug," police said.

None of the victims lived in the South Side building, a public relations firm representing the building told the Post-Gazette in a statement.

“It is important to note that the individuals that were involved in the incident were not residents of our community,” the statement said. “These were acquaintances of a good standing resident, who apparently was not in the apartment at the time the individuals were found. It is our understanding that the group had attended an outside event where they may have consumed a toxic substance before returning to the apartment.”

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Building spokesman Mark Winters told the paper it was unclear how the men were able to enter the building and apartment when the resident wasn't there.

Anyone with information has been asked to call police at (412) 323-7141.