Technique

Specimen collection prior to commencement of antimicrobial therapy provides the greatest yield. No specific contraindications exist as such:

• A cotton, rayon, or dacron-tipped, wire-mounted swab is ideal. In females, a non-bristled cytology brush may be used. A separate swab is used for each different pathogen being tested for. In addition, if testing for T. vaginalis, two swabs are required (see below)

• A first early-morning sample, prior to micturition, is ideal but often impractical

• Any exudate can be expressed by "milking" the urethra

• If material is not readily obtained, the swab is inserted 3-4 cm in to the anterior urethra

• Leave the swab in for a few seconds to allow saturation with the exudate (N. gonorrhea inhabits the exudate)

• If testing for Chlamydia, the swab must be rotated through 360° a few times to dislodge epithelial cells (Chlamydia is strictly intracellular within the urethral epithelial cells)

• Swabs for N. gonorrhea are transported in a container neutral agar, while Chlamydia containers have a special sucrose-phosphate medium with 5% fetal calf serum (often with added gentamicin to inhibit other microorganisms). One of the two swabs taken for T. vaginalis identification is placed in a tube containing 0.5 ml of sterile normal saline and transported immediately for direct wet mounts and cultures

• Swabs must be kept at room temperature and refrigeration should be avoided due to the susceptibility of these organisms to fluctuations in temperature

• Specimen must be sent to the laboratory within 6 hours, as the recovery rate of microorganisms decreases after this period

• The traditional method of diagnosis is to examine a gram-stained preparation of the urethral swab smear for identification of the pathogen. Newer techniques have improved detection rates

• Efficient method of diagnosing STI

• High sensitivity (79-97%) and specificity (87-99%)

• A negative test does not necessarily exclude infection, especially with persistent symptoms

• Recent urine based tests for Chlamydia and T. vaginalis have superseded urethral sampling

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