"This is a very, very tragic case," Spota said in a telephone interview. "We believe he definitely had sexual contact with other young males. This could possibly develop into a significant number."
Robert Musmacker, a 36-year-old newspaper deliveryman from Oceanside, pleaded not guilty to a nine-count indictment at his arraignment in Suffolk County Court in Riverhead.
Musmaker's attorney, Jack Byrnes, did not immediately return a telephone call seeking comment.
Musmacker was required to register as a Level 3 sex offender under Megan's Law because of a 1991 sodomy conviction involving a 6-year-old relative, said a spokesman for Spota. He was released from prison in January 2001.
He was stopped by a state trooper on the Southern State Parkway in West Babylon at about 6 a.m. on Dec. 28 with the 16-year-old, who was not identified, in the passenger seat. The trooper noticed that Musmacker's belt was undone, authorities said.
Musmacker possessed AIDS medication, which he said was for treatment of "full blown AIDS," the prosecutor said. He also advised the officer he was taking antibiotics to treat an open lesion in his mouth.
Both Musmacker and the boy told authorities they had engaged in sex on a number of occasions, Spota said. Authorities declined to provide even scant details about the boy's background or where the two may have met, citing an ongoing investigation.
Spota said despite Musmacker's admissions, prosecutors will seek a court order requiring him to undergo medical tests.
Besides reckless endangerment, Musmacker is charged with committing a criminal sex act, endangering the welfare of a child and several traffic violations. He is due back in court on Feb. 3.
The Musmacker case is somewhat reminiscent of the 1990s prosecution of Nushawn Williams, an HIV-positive man who admitted trading drugs for sex with girls in upstate New York. He knowingly infected at least 13 women with HIV and was sentenced to serve four to 12 years in state prison.
State police said other potential victims should call its Major Case Bureau at 631-756-3390.