A 31-year-old woman presents at the emergency department with fever for the past two days and a burning sensation while urinating over the past few weeks. She reports having unprotected sex with multiple partners over the past six months. Past medical history is significant for eczema and asthma. She does not currently take any medications. Vital signs are temperature 37.9°C (100.2°F), blood pressure 118/74 mm Hg, pulse 94 beats/minute, and respirations 16/minute. On physical examination, purulent cervical discharge is evident and cervical motion tenderness also noted.
WWhich of the following is the most appropriate investigation for the definitive diagnosis of the most likely etiology of this patient’s symptoms?
- A) Dark field microscopy
- B) Giemsa stain and microscopy
- C) Gram staining followed by culture
- D) Nucleic acid amplification testing (NAAT)
- E) Serologic testing for antibodies
D) Nucleic acid amplification testing (NAAT)
The most common causative organism of sexually transmitted infection (STI) in the United States is Chlamydia trachomatis (D-K subtypes). It causes urethritis that can present as in this patient with dysuria as well as with fever and cervicitis manifested by purulent cervical discharge and cervical motion tenderness. This patient is at risk for pelvic inflammatory disease (PID), salpingitis that can lead to an ectopic pregnancy later, and endometritis, among many other conditions. Chlamydia are atypical organisms that cannot be stained using a regular Gram stain due to the lack of a typical peptidoglycan layer. Polymerase chain reaction (PCR) or nucleic acid amplification testing (NAAT) is the diagnostic investigation of choice for Chlamydia.
Answer choice A: Dark field microscopy, is incorrect. Dark field microscopy is most commonly done on samples from a painless syphilitic chancre, a lesion that marks the onset of stage 1.
Answer choice B: Giemsa stain and microscopy, is incorrect. Giemsa stain can be used to stain Chlamydial organisms, but it is not the investigation of choice.
Answer choice C: Gram staining followed by culture, is incorrect. Atypical organisms like Chlamydiae, Rickettsiae, and Legionellae, among others, do not take Gram stain well due to an atypical peptidoglycan layer that contains much lesser muramic acid.
Answer choice E: Serologic testing for antibodies, is incorrect. Option B: Serological testing for antigens or antibodies is not done for chlamydia.
Key Learning Point
The investigation of choice for diagnosis of Chlamydia infection is nucleic Acid Amplification Testing (NAAT) or PCR.