Microbiology
Genitourinary and Sexually Transmitted Infections
Urinary and sexually transmitted infections for MBBS: UTI diagnosis, gonorrhoea, chlamydia, syphilis, genital ulcers and vaginitis, mapped to NMC codes MI7.1 to MI7.3.
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Genitourinary and Sexually Transmitted Infections
Urinary and sexually transmitted infections for MBBS: UTI diagnosis, gonorrhoea, chlamydia, syphilis, genital ulcers and vaginitis, mapped to NMC codes MI7.1 to MI7.3.
This chapter covers infections of the urinary and genital tracts. It deals with urinary tract infection and its laboratory diagnosis, the major sexually transmitted infections including gonorrhoea, chlamydia, syphilis and genital ulcers, vaginal infections, and the syndromic approach used in public health.
High-yield: Genitourinary and Sexually Transmitted Infections
- Escherichia coli is by far the commonest cause of urinary tract infection in the community.
- A significant urine culture is traditionally defined as 100,000 or more colony-forming units per millilitre of a single organism in a clean-catch sample.
- Staphylococcus saprophyticus causes urinary tract infection in young sexually active women.
- Proteus mirabilis produces urease, raises urine pH and predisposes to struvite stones.
- Neisseria gonorrhoeae causes urethral discharge and is seen as Gram-negative intracellular diplococci in a urethral smear.
- Chlamydia trachomatis is the commonest cause of non-gonococcal urethritis and is diagnosed by nucleic acid amplification.
- Treponema pallidum causes syphilis, whose primary lesion is the painless chancre.
- Syphilis is screened by non-treponemal tests such as VDRL and confirmed by treponemal tests such as TPHA.
- Haemophilus ducreyi causes chancroid, a painful genital ulcer with ragged edges.
- Herpes simplex virus type 2 causes painful recurrent genital ulcers.
- Human papillomavirus causes genital warts and its high-risk types cause cervical carcinoma.
- Trichomonas vaginalis causes a frothy greenish vaginal discharge and is seen as a motile flagellate on wet mount.
- Bacterial vaginosis shows clue cells, a raised vaginal pH and a positive whiff test with potassium hydroxide.
- Candida albicans causes vulvovaginal candidiasis with thick white discharge and itching.
- The syndromic approach treats sexually transmitted infections by symptom pattern when laboratory tests are not immediately available.
Genital ulcers, painful versus painless
- **Syphilis (primary):** Treponema pallidum. Single painless chancre with a clean base.
- **Chancroid:** Haemophilus ducreyi. Painful ulcer with ragged undermined edges.
- **Genital herpes:** Herpes simplex virus type 2. Painful grouped vesicles and recurrent ulcers.
- **Lymphogranuloma venereum:** Chlamydia trachomatis. Transient ulcer with painful inguinal buboes.
NMC competencies in this chapter
- **MI7.1:** Urinary tract infections: aetiology, pathogenesis and risk factors
- **MI7.2:** Sexually transmitted infections and their causative organisms
- **MI7.3:** Laboratory diagnosis, syndromic management and prevention
Frequently Asked Questions
What counts as a significant urine culture?
In a clean-catch midstream sample, 100,000 or more colony-forming units per millilitre of a single organism is the classic threshold for significant bacteriuria, though lower counts can matter in symptomatic patients.
How is syphilis diagnosed serologically?
Non-treponemal tests such as VDRL and RPR are used for screening and monitoring treatment, while treponemal tests such as TPHA and FTA-ABS confirm infection because they detect specific antibodies.
How are painful and painless genital ulcers distinguished?
The primary syphilitic chancre is painless, whereas chancroid due to Haemophilus ducreyi and genital herpes are painful, which is a useful first clinical clue before laboratory confirmation.
What is the syndromic approach to sexually transmitted infections?
It is a public-health strategy that groups infections by symptom pattern, such as urethral discharge or genital ulcer, and treats the likely causes together when immediate laboratory confirmation is not available.
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