Sexually Transmitted Infections (STIs)

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management

Definition

Sexually transmitted infections (STIs) are infections transmitted through sexual contact, including vaginal, anal, and oral intercourse. STIs may be bacterial, viral, parasitic, or fungal.

Aetiology

  • Bacterial: chlamydia (Chlamydia trachomatis), gonorrhoea (Neisseria gonorrhoeae), syphilis (Treponema pallidum).
  • Viral: HIV, human papillomavirus (HPV), herpes simplex virus (HSV), hepatitis B and C.
  • Parasitic: trichomoniasis (Trichomonas vaginalis).
  • Fungal: candidiasis (Candida albicans).

Pathophysiology

  • STIs are transmitted via mucosal contact, leading to local or systemic infection.
  • Bacteria and viruses target genital, anal, or oropharyngeal tissues.
  • Immune response may lead to inflammation, ulceration, or systemic dissemination.

Risk Factors

  • Unprotected sexual intercourse.
  • Multiple sexual partners.
  • Previous history of STIs.
  • Men who have sex with men (MSM).
  • Sex workers and individuals with high risk exposure.

Signs and Symptoms

  • Chlamydia: asymptomatic or causes dysuria, vaginal/urethral discharge, intermenstrual/postcoital bleeding.
  • Gonorrhoea: purulent discharge, dysuria, pelvic pain.
  • Syphilis: painless genital ulcer (primary), rash on palms/soles (secondary), neurological/cardiovascular complications (tertiary).
  • Herpes simplex virus (HSV): painful genital vesicles, flu like symptoms.
  • Trichomoniasis: frothy, yellow green vaginal discharge, vulvar irritation.
  • HPV: genital warts, cervical dysplasia.

Investigations

  • Nucleic acid amplification test (NAAT): gold standard for chlamydia and gonorrhoea detection.
  • Serology: syphilis (treponemal tests), HIV, hepatitis B and C.
  • Microscopy: wet mount for trichomoniasis.
  • HPV screening: cervical smear for high risk HPV types.

Management

1. Antibiotic and Antiviral Therapy:

  • Chlamydia: doxycycline (7 days) or azithromycin.
  • Gonorrhoea: ceftriaxone IM + azithromycin.
  • Syphilis: benzathine penicillin G IM.
  • Herpes simplex: aciclovir or valaciclovir.

2. Partner Notification and Screening:

  • Test and treat sexual partners.
  • Routine STI screening for high risk populations.

3. Preventative Measures:

  • Condom use and safe sex education.
  • HPV vaccination.
  • HIV pre exposure prophylaxis (PrEP) for high risk individuals.

4. Referral:

  • Genitourinary medicine (GUM): for specialist management of STIs.
  • Infectious diseases: for complex HIV or syphilis cases.
  • Gynaecology: for HPV related cervical dysplasia.
Infectious DiseasemypanotesSexually Transmitted Infections (STIs)