Diagnosis of gonorrhoea

History and examination are suggestive but definitive diagnosis can only be made by identifying the organisms in smears or by culturing them in special media - Thayer Martin. Smears may be obtained from genital discharge, blood, tissue, synovial fluid, the genitourinary tract or skin.

When choosing the approach and method used for detection of N. gonorrhoeae, prevalence of the disease in the local population should be considered (1). Detection of N. gonorrhoea can be achieved by

• microscopic examination of Gram stained smears
  • in men
    • has good sensitivity (90-95%) in men with urethral discharge and is recommended to facilitate immediate diagnosis in symptomatic men
    • should be carried out in men with rectal symptoms
  • in women
    • has poor sensitivity for the identification of gonococcal infection (37–50% for endocervical smears and 20% for urethral smears) (1)
• Nucleic acid amplification tests (NAAT)
  • more sensitive than culture and offer testing on a wider range of specimen types
  • shows high sensitivity (>96%) in both symptomatic and asymptomatic infection
  • preferred sample for NNAT in
    • men is first pass urine
    • women is vaginal or endocervical swab specimens
  • in extra genital sites (rectal and pharyngeal specimens)
    • use of NAATs is superior to culture for extragenital sites
    • NNAT is the method of choice for extra-genital sites in men who have sex with men (MSM) and other high-risk individuals
    • a positive result using NAATs with either a rectal or pharyngeal specimen is always confirmed using a supplementary test with a different target to prevent high numbers of false positives
• culture
  • offers a specific, sensitive and cheap diagnostic test at genital sites
  • allows confirmatory identification and antimicrobial susceptibility testing (2).

Transport of the organism should be in a suitable transport medium to the microbiology laboratory. Ideally, it should reach the lab within 24 hours (1).

Co-infection with Chlamydia is reported in 20-40 % of cases (3). Testing for C. trachomatis infection in persons undergoing testing for genital tract gonorrhoea is usually done using a dual NAAT (1).

Reference:

• (1) Bignell C, Fitzgerald M; Guideline Development Group.UK national guideline for the management of gonorrhoea in adults, 2011. Int J STD AIDS. 2011;22(10):541-7.
• (2) Health Protection Agency (HPA) 2010. Guidance for gonorrhoea testing in England and Wales.
• (3) RCGP and BASHH (2006) Sexually transmitted infections in primary care. Royal College of General Practitioners.
• (4) Prescriber 2003; 14(24):24-31.