Massive Ascites and Adnexal Masses Mimicking Malignancy: A Case Report of Chlamydia trachomatis Infection Diagnosed by Metagenomic Next-Generation Sequencing

Objective Chlamydia trachomatis ( C. trachomatis ) is the most commonly reported bacterial sexually transmitted infection among sexually active women. Although often asymptomatic or associated with non-specific clinical manifestations, it can cause inflammatory exudates and encapsulated fluid collections that are similar to adnexal masses on imaging. In rare cases, it may also present with massive ascites, a constellation of findings that may mimic ovarian malignancy. Case We report the case of a 32-year-old female with a nearly 3-month history of abdominal pain, adnexal masses and massive ascites. The initial workup did not reveal obvious evidence of infection and cytological examination showed no malignant cells. However, advanced gynecological originated cancer could not be fully excluded. Metagenomic next-generation sequencing (mNGS), which detected C. trachomatis in ascitic fluid, facilitated the diagnosis. The patient showed satisfactory clinical improvement following doxycycline treatment. Conclusion For young, sexually active women presenting with unexplained ascites and adnexal masses, after excluding malignancy and common infectious diseases such as tuberculosis , C. trachomatis infection should be considered. Modern etiological detection methods, such as mNGS, can be employed to facilitate the diagnosis.