Chlamydia trachomatis serovars L1, L2, and L3 cause lymphogranuloma venereum (LGV). The diagnostic test of choice in a patient with painful inguinal lymphadenopathy following unprotected sexual contact is:
- A Culture of C. trachomatis in McCoy cell monolayers
- B Frei test (intradermal injection of LGV antigen)
- C NAAT (PCR) on urethral/rectal swab or LN aspirate with genotyping for L serovars ✓
- D Serum complement fixation test (CFT) titer ≥1:64 for Chlamydia
Explanation
The Frei test (intradermal injection of heat-inactivated LGV antigen) was historically used but has poor sensitivity and specificity and is no longer recommended. NAAT (PCR) from the affected site (urethral/rectal swab, LN aspirate, or ulcer swab) is the diagnostic method of choice for LGV — it is highly sensitive and can be followed by genotyping (restriction fragment length polymorphism or sequencing) to confirm L1/L2/L3 serovars. Serum CFT titer ≥1:64 is supportive but non-specific. Culture is impractical and insensitive for LGV. Doxycycline 100 mg twice daily for 21 days is the treatment.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.