Agency concedes it doesn't know how dentist transmitted HIV. (U.S. Centers for Disease Control)

U.S. CDC

Researchers have concluded they may never know how a Florida dentist directly infected five of his patients with HIV.

In the May 15, 1992, issue of the Annals of Internal Medicine, the U.S. Centers for Disease Control (CDC) and Florida health officials conceded defeat in their two-year investigation of the dentist who died in 1990. A CDC official said no further investigation would occur unless another of the dentist's patients develops the disease.

Researchers did rule out several possibilities. They said the dentist did not deliberately infect the five; none of the patients had sex with the dentist, ruling out one means of spreading …