The victim was allegedly raped for a second time at the Mahatma Ghandi Medical College in the city of Jamshedpur, in India.
Days before, the girl had been raped by a teenage boy from her neighbourhood.
The hospital security guard has been identified by Indian police as Shambhu Mahato.
Twelve fellow security guards, including a woman, have also been detained for allegedly helping Mr Mahato flee the scene after the alleged crime.
Jamshepur superintendent of police, Chandan Jha, said a criminal investigation is now underway.
He said:“We’ve arrested the accused but further action will be initiated after we get the victim’s medical report. We’ve asked the doctors to submit the report within 48 hours. Investigation is on in the case and we want concrete evidence before acting further.”
Police said the girl, who cannot be identified for legal reasons, checked into hospital on Saturday after being raped by a teenage boy on January 26.
While at the hospital the security guard accompanied the girl to the bathroom and allegedly raped her, Express reported.
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