It was not clear whether the shooter was among those treated, and Fang declined to provide additional information until he was sure all the victims' families had been notified.
Police are still actively investigating the scene but believe there is no further danger to the community.
"Our prayers are with all those impacted, including our first responders", Logan said.
It appears there was only one weapon, a handgun, that was used and there were no shots fired by responding law enforcement officers, Gahler said.
She says the patients were brought there because it was the closest trauma center to the distribution center in Harford County. "For updates please follow @Harford_Sheriff", the agency tweeted.
Susan Henderson, spokesperson for the drugstore chain Rite Aid, said the shooting happened on the campus of a company distribution centre in Aberdeen.
FOX 5's Annie Yu spoke with Alexie, who said she was just getting out of bed when she received the texts. "This is part of a large facility that is a distribution center". She said she didn't know if the shooter was a Rite Aid employee.
He said a total of seven people were hit by gunfire and that four, including the woman who opened fire, were killed. And in 2016, two sheriff deputies were shot and killed at a Panera restaurant in Harford County.