Participants will collect a self-administered anorectal and vaginal swab at 8 time-points: pre-treatment during the visit at the STI clinic at which the treatment is given (T0), and at the end of weeks 1, 2, 4, 6, 8, 10, and 12. At T0, T4, T8 and T12 (visits at the clinic), the participants take an additional self-administered anorectal and vaginal swab that is otherwise exactly the same as the home-taken samples, but stored in a different buffer and processed immediately, i.e. cooled at -80°C within 24 hours, to allow CT viability testing. At the clinic visit, we will also consider to obtain a nurse-taken pharyngeal swab for later CT testing. For self-collection of the anorectal and genital samples, participants receive clear instructions.