Conjunctival swab/fluid

Specimen:

Separate swabs are required for inoculation of bacterial, viral and chlamydial transport media.

For suspected bacterial infection, swab or fluid should be directly smeared onto microscope slides and cultured on agar plates at the bedside.

Method:

Gram stain, NAA testing for chlamydia, culture for bacteria, chlamydia, fungi, viruses and amoebae (if keratitis present).

See also Chlamydia trachomatis nucleic acid.

Application:

Diagnosis of severe and/or persistent conjunctivitis, keratitis.

Interpretation:

The cause of conjunctivitis is established by the isolation of primary pathogens eg, Streptococcus pneumoniae, Haemophilus influenzae, Neisseria gonorrhoeae, Chlamydia trachomatis or Streptococcus pyogenes.

The culture of organisms such as Staphylococcus aureus, Staphylococcus epidermidis, Moraxella spp, Pseudomonas spp or coliforms may reflect non-pathogenic flora but in certain circumstances these organisms can be pathogenic.

Examination of the swab/fluid may allow diagnosis of herpes simplex, varicella zoster, fungal or acanthamoebic keratitis, although culture of corneal scrapings/biopsy will give a higher yield.

Reference:

Barnes SD et al. In: Mandell et al. Principles and Practice of Infectious Diseases. 6th ed. Churchill Livingstone 2005.