What are the initial diagnostic labs for disseminated Chlamydia (Chlamydia trachomatis)?

Diagnostic Labs for Disseminated Chlamydia Trachomatis

For diagnosing disseminated Chlamydia trachomatis infection, nucleic acid amplification tests (NAATs) from appropriate specimens are the initial diagnostic tests of choice due to their high sensitivity and specificity.

Specimen Collection Based on Clinical Presentation

• For suspected disseminated Chlamydia trachomatis infection, specimens should be collected from all potentially infected sites based on clinical presentation 1:

  • Genital specimens (cervical, vaginal, or urethral swabs)
  • First-catch urine specimens
  • Conjunctival swabs (if ocular involvement)
  • Nasopharyngeal specimens (if respiratory involvement)
  • Synovial fluid (if joint involvement)

• Tissue culture remains the definitive standard for diagnosing chlamydial infections, especially in cases requiring high specificity (such as legal cases) 1

Recommended Diagnostic Tests

• Nucleic Acid Amplification Tests (NAATs):

  • Most sensitive and specific tests available for C. trachomatis detection 2
  • Options include:
    • Polymerase chain reaction (PCR) tests
    • Transcription-mediated amplification (TMA)
    • Strand displacement amplification (SDA)
  • NAATs can detect C. trachomatis from urine samples with sensitivity of 96-100% and specificity of 98.8-100% 2

• Non-NAAT Options (less sensitive but sometimes necessary):

  • Direct fluorescent antibody (DFA) tests 1
  • Enzyme immunoassays (EIA) 1
  • Culture (especially important for legal cases or suspected abuse) 1

Special Considerations for Specimen Collection

• Specimens must contain cells, not just exudate 1
• For ocular specimens, swabs should be obtained from the everted eyelid using a dacron-tipped swab or manufacturer-specified swab 1
• For respiratory specimens in infants with suspected chlamydial pneumonia, collect specimens from the nasopharynx 1

Confirmatory Testing

• When a positive NAAT result is obtained, confirmation may be performed by:

  • Repeating the original test on the original specimen 3
  • Testing the original specimen with a different NAAT 3
  • Performing a different test on a duplicate specimen 3

• Confirmation rates of 84-98% can be achieved when retesting positive samples with the same NAAT 3

Additional Testing Considerations

• Test for co-infections:

  • All patients with chlamydial infection should be tested for other STIs including gonorrhea, syphilis, and HIV 1
  • Ocular exudate from infants being evaluated for chlamydial conjunctivitis should also be tested for N. gonorrhoeae 1

• For suspected chlamydial pneumonia in infants:

  • Consider peripheral eosinophilia (>400 cells/mm³) which frequently occurs 1
  • Chest radiograph typically shows hyperinflation and bilateral diffuse infiltrates 1

Pitfalls and Caveats

• False-negative results may occur early in infection due to small numbers of organisms 1
• False-positive results can occur with some non-culture tests, particularly in low-prevalence populations 4
• Non-culture, non-amplified probe tests should not be used in children due to the possibility of false-positive results 1
• For legal cases or suspected abuse, only cell culture isolation using standard methods with C. trachomatis-specific antibodies should be used 1