Wilmington, DE – A total of seven people received treatment following exposure to carbon monoxide in Wilmington Thursday, officials announced that afternoon.

According to the Wilmington Fire Department, units were dispatched to 620 West 26th Street at approximately 8:01 a.m. on November 5, 2015, for reports of sick persons, and arrived to find several occupants displaying flu-like symptoms.

Multi-gas meters determined carbon monoxide was present at a level of 700 parts-per-million, and officials discovered an unvented hot water heater in the basement was the cause.

According to fire officials, seven occupants received treatment at the scene, and six were additionally transported to local hospitals for additional treatment–two adults were transported to Christiana Hospital, two adults were transported to Wilmington Hospital, and two children were transported to A.I. DuPont Children’s Hospital. One occupant refused further treatment.

Nearby properties were ventilated and the situation was placed under control at 8:39 a.m., Wilmington fire officials said.