A 34-year-old woman presents to the clinic for routine sexually transmitted infection (STI) screening. She is asymptomatic and reports having 5 male sex partners during the past 3 years. Laboratory tests show a positive treponemal enzyme immunoassay (EIA) and a positive Rapid Plasma Reagin (RPR) at a titer of 1:64. Tests for HIV and other STIs are negative. Her last screening for STIs (including syphilis) was about 3 years ago. She has no history of syphilis or other bacterial STIs. A diagnosis of late latent syphilis is made, and she is treated with three doses of intramuscular benzathine penicillin G 2.4 million units, administered at 1-week intervals (total dose of 7.2 million units).