Non-responders at 6 months in the doxycycline and penicillin group who had completed 6 months of follow-up.

Note: "3 month follow-up (−)" indicates patients had no follow-up of RPR titer at 3 months of treatment, while " 3 month follow-up (+)"indicates patients had follow-up of RPR titer; "6 month follow-up (−)" indicates patients had no follow-up of RPR titer at 6 months of treatment, while "6 month follow-up (+)" indicates patients had follow-up of RPR titer.§Re-infection: development of new symptoms of primary syphilis and secondary syphilis; or a 4-fold or greater increase of RPR titer after ever achievement of 4-fold or greater decline following treatment.§§Treatment failure: failure of RPR titer to decrease by 4 folds or greater, or receipt of another course of treatment without demonstrated serological response throughout the follow-up period.aThere was 1 case of secondary syphilis in the doxycycline group, while there were 2 cases of primary, 3 secondary, and 2 primary as well as secondary syphilis in the penicillin group.Non-responders at 6 months in the doxycycline and penicillin group who had completed 6 months of follow-up.