Have human immunodeficiency virus (HIV) infection
and engage in any of the behaviors listed above.
Syphilis is contagious whenever an open sore or skinrash
is present. The risk of being infected with syphilis from a single sexual
encounter with an infected partner is approximately 3% to 10%.4
Infection with syphilis also increases a
person's risk of being infected with HIV. Syphilis causes open sores on the
genitals that allow the HIV infection to enter the body easily. Syphilis is
in general more common in people who are also infected with HIV.