Police in the US city of Pittsburgh are investigating how seven people all wearing orange wristbands were involved in a fatal “medical situation”.
Three have died and the other four are in conditions ranging from serious to critical. Four were found in a flat, one in a lift and one on the street.
No immediate drugs paraphernalia was found and the flat’s building was not said to be at risk.
Police asked for information on any party that had given out wristbands.
Pittsburgh director of public safety Wendell Hissrich said all the victims were believed to be middle-aged men.
Officers responded to a call about an unconscious man at about 02:00 (06:00 GMT).
One man was found on 26th and Carson streets and taken to hospital. Another was found in a lift at Southside Works City Apartments. He later died.
Information led police to the flat, where another two men were found dead and three more were discovered needing hospital treatment.
“We have no indication there was a party there,” Mr Hissrich said of the flat, adding that the building’s air quality had been checked and there was no danger.
Hospitals have been put on alert for anyone checking in wearing an orange wristband or with similar medical symptoms.