A multicentre prospective cohort study is set up with biological and behavioural measurements after routine treatment of CT. During 3 months, the participants will be studied using a self-administered anorectal and vaginal swab that is self-collected pre-treatment (T0), and at the end of weeks 1, 2, 4, 6, 8, 10, and 12. Samples are tested using NAAT for presence of CT-DNA (detection), concentration (load), viability (weeks 4,8, and 12), and CT type (multilocus sequence typing-MLST) to confirm re-infection. To validate sexual exposure, chromosomal Y DNA (as a marker for semen exposure) in genital and anorectal samples is applied. At each sampling time, online self-administered questionnaires on behaviour (e.g. anorectal exposure) and symptoms will be completed.