Laboratory Diagnosis, Treatment, Prevention and Control of Chlamydia trachomatis 5/5 (9)

Laboratory Diagnosis of Chlamydia trachomatis

Specimen

• Urethral discharge, cervix swab, rectum, oropharynx, and conjunctiva swab are the frequently collected specimens.
• In addition, other specimens such as, blood, urine, respiratory secretions, sputum, lung, and other tissues are collected and examined.
• Pus from bubo is also useful for diagnosis of LGV.

Microscopy

• Demonstration of chlamydial inclusion bodies stained by Giemsa, Castaneda, Machiavello, Gimenez stains or Lugol’s iodine.
• C. trachomatis infections of conjunctiva, urethra, and cervix are diagnosed by demonstration of typical reniform inclusion bodies surrounding the nucleus.
• Direct Immunofluorescence test (DIF) is used as for direct detection of inclusion bodies in clinical material, particularly from the genital tract and eye.
• In DIF, fluorescent tagged monoclonal antibodies directed against group-specific LPS antigen or species-specific MOMP antigens are added.

Culture

• Isolation of C. trachomatis in cell cultures is the more specific method for diagnosis of C. trachomatis infection.
• Centrifugation of specimens onto cycloheximide treated McCoy or HeLa cell monolayers, followed by incubation and then staining with a fluorescent monoclonal antibody or with a vital dye, to detect inclusions, has been widely used for the diagnosis of C. trachomatis infection.

Figure: Chlamydia trachomatis is grown in cell cultures and detected by staining inclusion bodies (arrows) with either iodine- or specific fluorescein-labeled antibodies.

Antigen detection

• Two general approaches have been used to detect chlamydial antigens in clinical specimens: direct immunofluorescence staining with fluorescein-conjugated monoclonal antibodies and enzyme-linked immunosorbent assays.
• In both assays, antibodies are used that have been prepared against either the chlamydial MOMP or the cell wall LPS.
• The DFA uses monoclonal antibodies directed against a species-specific antigen on the chlamydial MOMP.
• The EIA detects the presence of genus-specific antigens extracted from EBs in the specimen.

Nucleic Acid–Based Tests

• Nucleic acid probe tests most commonly measure the presence of a species-specific sequence of 16S ribosomal RNA.
• The advantage of these tests is that the nucleic acid does not have to be amplified, making the tests rapid and relatively inexpensive; however, these tests are relatively insensitive for the detection of small numbers of chlamydiae.
• Various methods available are:
  • Polymerase chain reaction (PCR)
  • Ligase chain reaction (LCR)
  • Transcription-mediated amplification (TMA)
  • Strand displacement assay (SDA).

Antibody Detection

• Serologic testing is of limited value in the diagnosis of trachomatis urogenital infections in adults because the test cannot differentiate between current and past infections.
• C. trachomatis IgM antibody is the ‘gold standard’ for the diagnosis of chlamydial pneumonia in babies.
• Antibody tests for the diagnosis of LGV can be helpful.
• Infected patients produce a vigorous antibody response that can be detected by complement fixation (CF), microimmunofluorescence (MIF), or enzyme immunoassay (EIA).

Treatment of Chlamydia trachomatis Infection

• Tetracyclines and macrolides are the mainstay of treatment.
• Tetracyclines (eg, doxycycline) are commonly used in nongonococcal urethritis and in nonpregnant infected women.
• Azithromycin is effective and can be given to pregnant women.
• Ophthalmia neonatorum and neonatal pneumonia due to trachomatis should be treated with erythromycin.
• Erythromycin may be administered orally and topically for treatment of ophthalmia neonatorum.
• Systemic erythromycin is effective treatment in severe cases.
• Recommended treatment for LGV is doxycycline or erythromycin.
• Azithromycin has been used successfully in some cases.
• Ocular infection can be effectively treated with a single oral dose of azithromycin.

Prevention and Control of Chlamydia trachomatis Infection

• Health education and condom promotion, especially for the youngest sexually active age groups may help to reduce the incidence of genital C. trachomatis infection.
• Periodic screening of high risk groups, such as young women having multiple sex partners.
• Use of barrier methods of contraception such as condoms.
• Chlamydia conjunctivitis and genital infections are prevented through the use of safe sex practices and the prompt treatment of symptomatic patients and their sexual partners.
• The blindness associated with advanced stages of trachoma can be prevented only by prompt treatment of early disease and the prevention of re-exposure.
• Screening of mother giving birth to a child for Chlamydial infections.

Laboratory Diagnosis, Treatment, Prevention and Control of Chlamydia trachomatis