A 28-year-old woman presents to the gynaecology clinic with a 3-week history of mucopurulent cervical discharge and lower abdominal pain. She is sexually active with a new partner 6 weeks ago. Pelvic examination reveals cervical erythema and mucopurulent exudate. Gram stain of the cervical swab shows no intracellular gram-negative diplococci. Nucleic acid amplification test (NAAT) for Chlamydia trachomatis is positive. What is the most likely serovar involved in this presentation?

Explanation

## Clinical Diagnosis: Chlamydia trachomatis Urogenital Infection ### Serovar Classification and Clinical Correlation **Key Point:** Chlamydia trachomatis serovars are classified into three epidemiological groups based on clinical presentation and tissue tropism. | Serovar Group | Serovars | Clinical Presentation | Geographic Pattern | | --- | --- | --- | --- | | **Trachoma** | A, B, Ba, C | Chronic keratoconjunctivitis, blindness | Endemic in developing countries | | **Urogenital & Respiratory** | D–K | Cervicitis, urethritis, PID, neonatal conjunctivitis, pneumonia | Sexually transmitted, worldwide | | **Lymphogranuloma Venereum** | L1, L2, L3 | Painful inguinal lymphadenopathy, rectal strictures | Sexually transmitted, sporadic | ### Why Serovars D–K in This Case? 1. **Clinical presentation:** Mucopurulent cervical discharge with lower abdominal pain is classic for urogenital chlamydial infection. 2. **Absence of systemic lymphadenopathy:** Rules out LGV (serovars L1–L3), which presents with painful inguinal lymph node enlargement. 3. **Absence of ocular involvement:** Rules out trachoma (serovars A–C), which is endemic in resource-limited regions and presents with chronic keratoconjunctivitis. 4. **NAAT positivity:** Confirms chlamydial infection; serovars D–K are the most common sexually transmitted serovars worldwide. **High-Yield:** In sexually active individuals with urogenital symptoms and positive NAAT for *C. trachomatis*, assume serovars D–K unless there is clinical evidence of trachoma (endemic region, ocular involvement) or LGV (painful lymphadenopathy, proctocolitis). ### Pathophysiology of Urogenital Infection **Clinical Pearl:** Serovars D–K preferentially infect columnar epithelium of the endocervix, urethra, and rectum. They cause: - Acute cervicitis with mucopurulent discharge - Ascending infection → pelvic inflammatory disease (PID) - Neonatal transmission → ophthalmia neonatorum and pneumonia - Chronic sequelae: tubal scarring, ectopic pregnancy, infertility ### Diagnostic Confirmation **Key Point:** NAAT (PCR, TMA) is the gold standard for *C. trachomatis* detection. Gram stain is insensitive (only detects *Neisseria gonorrhoeae* as intracellular gram-negative diplococci in urethritis). Culture is slow and requires specialized media. ### Management Implications - **First-line:** Azithromycin 1 g single dose OR doxycycline 100 mg BD for 7 days - **Partner notification and treatment:** Essential to prevent reinfection - **Test of cure:** Not recommended routinely; repeat NAAT >3 weeks after treatment if symptoms persist