[Verified Answer]: A 19-year-old woman is noted to have a…

A 19-year-old woman is noted to have a rapid plasma reagin (RPR) titer of 1:16, and the confirmatory test (Treponema pallidum particle agglutination [TP-PA]) is positive. She has no history of syphilis. She is treated with benzathine penicillin G 2.4 million units intramuscularly. Six months after therapy, she is noted to have an RPR titer of 1:2. At 9 months, the titer is 1:1. Two months later, the repeat RPR is noted to be 1:16. Which of the following is the most likely diagnosis?