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- GUM, genitourinary medicine
- HPA, Health Protection Agency
- MSM, men who have sex with men
- NAATs, nucleic acid amplification tests
- PPV, positive predictive value
- STI, sexually transmitted infections
The organism Neisseria gonorrhoeae is a highly infectious, bacterial sexually transmitted pathogen that is frequently identified and treated in genitourinary medicine (GUM) clinics in the United Kingdom. In heterosexuals, its prevalence is associated with age (<25 years), black ethnicity, and socioeconomic deprivation. Population prevalence estimates from the Health Protection Agency suggest that it may be more prevalent in men who have sex with men (MSM) than in heterosexual men. Infection is frequently asymptomatic at the endocervix and urethra in women, and usually (>90%) asymptomatic in the rectum and oro-pharynx in both men and women.1 It is associated with significant morbidity. Testing for N gonorrhoeae is a core component of screening for sexually transmitted infection (STI) within GUM clinics.
Microscopy for intracellular Gram negative diplococci
Microscopic examination of Gram stained smears of urethral discharge in men or endocervical discharge can be used as a near patient test to provide an immediate presumptive diagnosis of gonorrhoea (evidence level II, recommendation grade B). In men, microscopy of urethral smears has a sensitivity of >95% in symptomatic patients, lower in asymptomatic patients (50–75%).1–4 Microscopy of endocervical smears in women has a sensitivity of between 30–50%. Specificity is high when screened by trained personnel, >99%.2–4 Microscopy is not suitable for pharyngeal or rectal specimens where many other bacteria are present, including Gram negative cocci belonging to other genera.4,5
Isolation of N gonorrhoeae
Specimens collected from an appropriate site should be cultured onto an enriched medium, usually GC agar base or Columbia agar, supplemented with lysed or chocolatised horse blood or a non-blood based supplement such as IsoVitaleX (Becton-Dickinson) or Vitox (Oxoid) (evidence level II, recommendation grade B). If a single medium is used this should contain antimicrobial agents as selective agents to suppress the normal flora and allow the growth of N gonorrhoeae (GC audit)6 (evidence level …
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