Doctors in New York City are describing the first known U.S. cases of sexually transmitted ringworm, which can cause a nasty rash that can take months to bring under control. Despite the name, ringworm isn't any kind of worm but instead is a fungus, Trichophyton mentagrophytes. It's more commonly known as jock itch (when it affects the groin area) or athlete's foot, and can produce a round, itchy rash. Advertisement Until now, transmission of the fungal infection through skin-to-skin sexual