Genital swab

Last updated: Friday, 30, November, 2007

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Item Process
Specimen
  1. Cervical swab collected from the endocervical canal during speculum examination;
  2. Vaginal swab;
  3. Combined low vaginal/rectal swab for detection of Group B steptococcus in pregnancy;
  4. Swab of urethral discharge and/or urethral sampling using fine wire swab.

Smears should be made directly on a clean glass slide.

Unfixed slides should be handled with care and transported to the laboratory in a suitable container. 

For detection of Chlamydia trachomatis and Neisseria gonorrhoeae by nucleic acid probe after PCR amplification, consult laboratory. Some assays use a dry swab while for others the swab must be discarded after special transport has been inoculated. Initial urine specimens are an alternative to genital swabs for detection of these organisms.

Method

Microscopy of wet film;
Gram stain and direct IF;
culture including Neisseria gonorrhoeae, Chlamydia trachomatis (specialised laboratories only), Candida albicans, Gardnerella vaginalis, Group B streptococcus (pathogenic in the neonate), Haemophilus influenzae.

Some laboratories also culture for Trichomonas vaginalis.

EIA and/or molecular genetics for Chlamydia trachomatis, Neisseria gonorrhoeae.

Application

Investigation of mucopurulent cervicitis (see Cervical lesion);
vaginal discharge;
urethral discharge (see Urethritis);
pelvic inflammatory disease;
endometritis;
postpartum fever;
screening for carriage of Group B streptococcus in pregnancy.

Interpretation

Microscopy of wet film: excess white cells suggest presence of infection; motile trichomonads indicates presence of trichomoniasis, yeasts and hyphae suggest candidiasis; 'clue' cells without an excess of white cells suggest Gardnerella vaginalis infection.     

Gram stain: the presence and relative numbers of pus cells and epithelial cells influence interpretation; presence of yeasts supports a diagnosis of candidiasis; intra- and extra-cellular Gram-negative diplococci suggest gonorrhoea.

Culture: results must be interpreted in conjunction with clinical information and the results of microscopy of wet film and Gram stain.

Nucleic acid probes (with or without PCR amplification) have a greater sensitivity for establishing the diagnosis of gonorrhoea and chlamydial infections.

See Molecular genetics - microbial.

Reference

McCormack WH and Rein MF. In: Mandell GR et al eds. Principles and Practice of Infectious Diseases. 6th ed. Churchill Livingstone 2005.

McCormack WH. In: Mandell GR et al eds. Principles and Practice of Infectious Diseases. 6th ed. Churchill Livingstone 2005.