The goal of this observational study is to learn if we can identify immune biomarkers in first-void urine and vaginal brush samples in Chlamydia trachomatis (CT) positive adult women. Participants will self-collect a first-void urine sample, self-collect a vaginal brush, and a blood sample will be collected by a healthcare worker. Participants will complete a questionnaire.

To date, clinician-collected blood samples are still the primary methods to monitor immune responses to genital tract infections. Replacing these samples with a specimen that is non-invasive and can be self-collected, such as the initial or first-void urine stream or vaginal brushes, could have important acceptance and feasibility advantages and could facilitate the logistics of clinical trials and future epidemiological or vaccine studies. Moreover, these local samples give more information on the immune response at the site of infection, in the genital tract. Initial results of experiments using first-void urine samples and cervicovaginal brushes for immune response monitoring are promising. However, no standardized method for the detection of (functional) Chlamydia trachomatis (CT)-specific immune responses is available to be used on first-void urine or vaginal samples. Therefore, the aim of this pilot study is to determine feasibility to detect mucosal immune responses in first-void urine and self-collected vaginal samples. Furthermore, we will compare local immune responses with systemic immunity.

The primary objectives of this study are:

• To explore the feasibility to detect (functional) CT-specific antibodies and CT-specific cellular immune responses in first-void urine or self-collected vaginal samples.
• To compare levels of total and CT-specific antibodies in first-void urine and serum.
• To compare mucosal and systemic CT-specific cellular immune responses in mucosal mononuclear cells derived from first-void urine or self-collected vaginal samples, and peripheral blood mononuclear cells (PBMCs).

A total of 73 female participants will be included in this trial. Women that can be included have to be positive for a Chlamydia trachomatis nuclear acid amplification test (NAAT) on a vaginal or FVU sample, and have not yet been treated with antibiotic therapy.

The study described is a low-interventional observational study. Participants will self-collect a first-void urine sample using a 20 mL Colli Pee® device (Novosanis), followed by a vaginal brush (Evalyn® brush, Rovers). Medical personnel at the study site will collect a blood sample (one serum tube and 2 heparin tubes). Furthermore, personal data is collected via a paper-based questionnaire.

Inclusion Criteria:

• Female
• Chlamydia trachomatis NAAT positive vaginal sample or first-void urine sample.
• Able to understand the information brochure and what the study is about.
• Willing to give informed consent to use their samples for details described in the study protocol.

Exclusion Criteria:

• Pregnancy (self-reported)
• Being positive for Human Immunodeficiency Virus (HIV)
• Women that underwent hysterectomy.
• Menstruation at the time of sample collection.
• Current use of antibiotics effective against Chlamydia trachomatis (doxycyline or azithromycine) or use of such antimicrobials in the past 14 days before participating in the study.
• Participating in another clinical trial at the same time of participating in this study.
• Having a history or current evidence of any condition or abnormality that might confound the results of the study or is not in the best interest of the individual to participate, in the opinion of the investigator.

A total of 73 Chlamydia positive female participants will be included.