Syphilis: continuing public health and diagnostic challenges.

As the "great imitator" of disease, syphilis, caused by the bacterium Treponema pallidum, continues to be a conceptually elusive condition that is surrounded by diagnostic ambiguity and clinical misunderstanding. Concurrent HIV infection adds further difficulty by introducing the oldest and most confusing medical conundrum into the socially and biologically complex situation of treating patients with a virus we are still only learning to manage. Syphilis continues to be a challenge to the health of men who have sex with men and people of color as infection rates continue to increase within these substantial subgroups living with HIV. As the resurgence of syphilis continues, a clear understanding of diagnostic testing, disease-staging paradigms, and treatment strategies are necessary for optimal management of the HIV co-infected patient.