DEXTER, Mo. >> A Missouri man who told authorities he had sexual contact with as many 300 people since being diagnosed with HIV pleaded not guilty today to infecting another man with the virus, and prosecutors said more charges are expected.

David Mangum entered the plea after being charged with recklessly infecting another with HIV, which in Missouri — where penalties for such crimes are among the nation’s harshest — carries a maximum sentence of life in prison. His attorney didn’t return messages seeking comment.

Court documents allege that the 36-year-old told detectives in Dexter, a small town in southeast Missouri, that he had unprotected sex with as many as 300 partners since being diagnosed a decade ago with HIV, the virus that causes AIDS. Up to 60 of those contacts allegedly occurred after he moved to Missouri two years ago from Dallas, where he has convictions for prostitution, indecent exposure and public lewdness.

Many of his trysts stemmed from Craigslist ads, he told investigators, and he would meet up with men at parks, truck stops and other remote locations. Police believe many were truckers or others passing through the region, and because Mangum had little information about many of the men, investigators are concerned about finding potential victims, Dexter police detective Cory Mills said.

“First names with no phone numbers or addresses — that’s going to be a challenge,” Mills said.

So authorities turned to the media, and since then more potential victims have come forward, Stoddard County prosecutor Russell Oliver said. Oliver wouldn’t say how many people, but he said more charges were expected.

Local health clinics are reporting a recent surge in people seeking HIV tests. In Stoddard County, where one or two people generally get tested each week, 15 people came in for testing in the past week, said Debbie Pleimling, director of the county’s Health Department. Neighboring counties are reporting a spike.

“There has to be concern,” she said. “If he’s randomly meeting people for sex, we have no clue where to turn.”

Local authorities said they were also working with Dallas police, who didn’t return several messages from The Associated Press.

It’s unclear why Mangum moved to Dexter, a conservative town of about 8,000 residents. He worked at a local grocery store, according to Mills, but little else is known about him.

“Everyone’s really surprised that sort of thing is going on here,” local barbershop owner Charlie Parrish said as he cut hair this week.

This summer, Mangum allegedly admitted to a roommate with whom he’d been intimate that he had been HIV-positive since 2003. The man went in for testing and learned he was HIV-positive, then went to police.

Mills said Mangum seemed unapologetic and told police he wasn’t truthful for “fear of rejection.”

Magnum is jailed on $250,000 cash-only bond. A preliminary hearing is set for Sept. 26.

Missouri is among 37 states that make it a crime to knowingly transmit HIV to others, though its penalties are among the toughest: a maximum sentence of life in prison if the victim was infected with HIV, and up to 15 years in prison if the victim was exposed.

In 2007, Angela Harris of St. Charles was sentenced to 10 years in prison for having unprotected six with her then-boyfriend and failing to tell him she was HIV-positive. The former boyfriend didn’t test positive for HIV. Cases have also been prosecuted in St. Louis, Springfield and rural Marshfield, where in 1999 a 21-year-old man was sentenced to five years in prison for deliberately exposing a woman to HIV.

HIV and AIDS cases aren’t broken down by county in Missouri. But for the 13-county Southeast region, Pleimling said 137 people are known to be living with HIV and another 174 with AIDS. A dozen people were diagnosed in the region last year.