She is board-certificated in internal medicine and infectious diseases and provides primary care to patients with HIV infection. Johnston's clinical research focuses on the natural history and pathobiology of genital herpes simplex virus (HSV) infection. She is interested in novel therapies to prevent and manage HSV infection, such as antiviral agents and vaccines. In addition, Johnston is the Medical Director of the University of Washington Sexually Transmitted Diseases Prevention Training Center, which educates health care providers about prevention and management of sexually transmitted infections (STI). Johnston earned her MD from the University of Minnesota Medical School in 2001.