Though names have not been released, the three persons transported to the hospital held the rank of corporal, colonel and gunnery sergeant, WJLA reported.
According to Leah Rubalcaba, spokesperson for the base, employees inside the building began to feel sick after "someone opened a letter." The US Army base is located near the Pentagon and near Arlington Cemetery, where US war veterans are buried with honors.
US Marine officials confirmed that initial symptoms of those who fell sick included irritations to the face, eye and skin and that one person began to bleed from their nose after the letter was opened. The official USMC Twitter page later indicated that after personnel fell ill, officials immediately followed preventative measures and evacuated the building.
The Arlington County Fire Department has taken to Twitter to reveal details about the incident.
The investigation has since been turned over to the FBI.
It is unclear who opened the letter and what it contained. Hazmat crews are examining the letter and conducting an investigation.