At least nine residents of Durham's McDougald Terrace public housing community have been taken to the hospital and treated for elevated levels of carbon monoxide, prompting officials on Friday to go door-to-door checking for the potentially toxic gas.

A woman was rushed to a local hospital for an evaluation after first responders found elevated levels of carbon monoxide in her unit at the complex, which is located at 1101 Lawson Street.

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The discovery has heightened fears at McDougald Terrace, where 344 apartments were checked for CO at the complex, which was first built in 1953.

It is Durham's largest public housing community, according to the DHA website, and it has been beset by poverty and violent crime in recent years.

The issue came to light when EMS Asst. Chief for Clinical Affairs Lee Van Vleet noticed a call on Dec. 23 for carbon monoxide poisoning, the one confirmed case at the complex.

Vleet looked at the history of calls for service for the month in that location and found that seven other people who were transported that month also had elevated levels of carbon monoxide in their systems.

Vleet noticed the trend and alerted other officials.

All nine incidents to date have occurred inside units located on Ridgeway Avenue, Vleet said.

During Friday's checks, officials from the Durham Housing Authority, firefighters and paramedics conducted reviews to determine if carbon monoxide detectors were functional in each unit.

Housing authority officials and first responders provided information about the chemical to residents in an effort to calm their fears.

Carbon monoxide is known as the silent killer because it is invisible and odorless.

The mother of the woman who was taken to the hospital Friday morning said she was unnerved by the turn of events.

"My heart is jumping," she said. "Because I live up the street, and I don’t know if it’s in my house or not."

Fire officials said exposure to carbon monoxide can make its victims feel sluggish and also be accompanied by flu-like symptoms.

Experts say the reasons why carbon monoxide poisoning can occur include when residents use a grill inside their home or use a stove to heat the inside of their house.

Officials say it's unclear where the gas is coming from at McDougald Terrace.