Story highlights David Mangum told police he has been HIV-positive since 2003

Since then, he had 300-plus unprotected sexual encounters, he told investigators

He could face up to 15 years in prison on the charge

Prosecutors in rural Missouri have charged a man with exposing his partner to HIV and say he may have exposed more than 300 other people to the virus that causes AIDS.

David Mangum told police he had at least that many unprotected sexual encounters with people he met online or in parks since he was diagnosed with HIV in 2003, Dexter, Missouri, detective Sgt. Corey Mills told CNN. Mills said it will be difficult to find and warn those people, since Mangum "usually only knew his partners' first names."

Mangum was arrested after his former partner told police that Mangum had lied to him about his status, a police affidavit states. He was arraigned Thursday morning in Stoddard County, about 160 miles south of St. Louis, with bail set at $250,000. The former partner has tested positive for HIV, according to police.

Mangum, 36, told police that between 50 and 60 of his partners lived in Stoddard County, according to court records.

Knowingly exposing someone to HIV without their consent is a felony under Missouri law that can bring prison terms up to 15 years. Infecting someone can bring a life term.