A 28-year-old woman presents with mucopurulent cervical discharge, dysuria, and lower abdominal pain for 2 weeks. Gram stain of endocervical swab shows no intracellular gram-negative diplococci. Which investigation is most appropriate to confirm the suspected diagnosis of Chlamydia trachomatis cervicitis?

Explanation

## Investigation of Choice for Chlamydia trachomatis **Key Point:** NAAT (PCR, TMA, SDA) is the gold standard for diagnosis of *Chlamydia trachomatis* infection — highest sensitivity (>95%) and specificity (>99%). **High-Yield:** NAAT is superior to all other methods because: - Detects organism DNA/RNA, not dependent on viable organisms - Can be performed on urine, endocervical, urethral, or rectal specimens - Does not require special transport media or immediate processing - Sensitivity ~95–98%; specificity >99% ### Why NAAT is the Gold Standard | Feature | NAAT | Culture | DIF | Giemsa | |---------|------|---------|-----|--------| | **Sensitivity** | 95–98% | 70–85% | 80–90% | 50–60% | | **Specificity** | >99% | >99% | 95–98% | 70–80% | | **Specimen type** | Urine, swab | Swab only | Swab only | Swab only | | **Viability required** | No | Yes | No | No | | **Speed** | 2–24 hrs | 48–72 hrs | 24 hrs | 1 hr | | **Cost** | Moderate | High | Low | Low | **Clinical Pearl:** In this case, the negative Gram stain rules out *Neisseria gonorrhoeae* (which shows gram-negative diplococci in polymorphonuclear leukocytes). The clinical presentation of mucopurulent cervicitis without gonococci is classic for *C. trachomatis*, and NAAT is the diagnostic standard. **Mnemonic: "NAAT Beats All"** — NAAT (Nucleic Acid Amplification Test) is the most sensitive and specific test for chlamydia; it beats culture (requires viability), DIF (lower sensitivity), and Giemsa (poor sensitivity).