Sexually Transmitted Infections (STIs)

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

Definition

Sexually transmitted infections (STIs) are infections that are primarily spread through sexual contact. They can be caused by bacteria, viruses, parasites, and fungi.

Types

Common types of STIs include:

• Chlamydia: Caused by Chlamydia trachomatis bacteria.
• Gonorrhoea: Caused by Neisseria gonorrhoeae bacteria.
• Syphilis: Caused by Treponema pallidum bacteria.
• Genital herpes: Caused by Herpes Simplex Virus (HSV) type 1 or type 2.
• Human papillomavirus (HPV): Causes genital warts and is associated with cervical and other cancers.
• HIV/AIDS: Caused by the Human Immunodeficiency Virus.
• Trichomoniasis: Caused by the parasite Trichomonas vaginalis.
• Hepatitis B: Caused by the Hepatitis B virus (HBV).

Aetiology

STIs are caused by various pathogens:

• Bacterial STIs: Chlamydia, Gonorrhoea, Syphilis.
• Viral STIs: Genital herpes, HPV, HIV/AIDS, Hepatitis B.
• Parasitic STIs: Trichomoniasis.
• Fungal STIs: Candidiasis (less commonly classified as an STI).

Pathophysiology

The pathophysiology of STIs varies with the causative pathogen but generally involves:

• Transmission through sexual contact, including vaginal, anal, and oral sex.
• Infection of the genital tract, which may spread to other parts of the body.
• Damage to tissues and induction of inflammatory responses.
• Potential for systemic involvement, especially in viral infections like HIV/AIDS and hepatitis B.

Risk Factors

• Having multiple sexual partners
• Unprotected sex (not using condoms)
• Previous history of STIs
• Substance abuse (which may lead to risky sexual behaviours)
• Young age (especially adolescents and young adults)
• Men who have sex with men (MSM)
• Sex workers
• Immunocompromised individuals

Signs and Symptoms

The signs and symptoms of STIs vary widely but can include:

• Genital sores or ulcers
• Genital warts
• Unusual discharge from the penis or vagina
• Burning sensation during urination
• Itching or irritation in the genital area
• Pain during intercourse
• Swollen lymph nodes
• Fever
• Rash

Investigations

Specific investigations to diagnose STIs include:

• NAAT (Nucleic Acid Amplification Tests): For detecting bacterial and viral DNA or RNA (e.g., chlamydia, gonorrhoea, HIV).
• Serology: Blood tests to detect antibodies (e.g., HIV, syphilis, hepatitis B).
• Microscopy and culture: Examination of samples (e.g., discharge, swabs) for parasites and bacteria.
• Visual inspection: For genital warts and other visible lesions.
• Pap smear: For detecting HPV-related changes in cervical cells.

Management

Primary Care Management

• Antibiotics: For bacterial STIs (e.g., azithromycin or doxycycline for chlamydia; ceftriaxone and azithromycin for gonorrhoea).
• Antivirals: For viral STIs (e.g., acyclovir for genital herpes, antiretroviral therapy for HIV).
• Antiparasitics: For parasitic STIs (e.g., metronidazole for trichomoniasis).
• Vaccination: For prevention of certain STIs (e.g., HPV and hepatitis B vaccines).
• Education and counselling: On safe sex practices and the importance of notifying sexual partners.

Specialist Management

• Referral to a specialist: For complicated cases or if co-infection with HIV is suspected.
• Management of complications: Such as pelvic inflammatory disease (PID), epididymitis, or complications from HIV/AIDS.
• Public health measures: Reporting and partner notification to prevent the spread of STIs.

References

1. NHS (2024) Sexually transmitted infections (STIs). Available at: https://www.nhs.uk/conditions/sexually-transmitted-infections-stis/ (Accessed: 24 June 2024).
2. Centers for Disease Control and Prevention (2024) Sexually Transmitted Infections (STIs). Available at: https://www.cdc.gov/std/default.htm (Accessed: 24 June 2024).
3. World Health Organization (2024) Sexually transmitted infections (STIs). Available at: https://www.who.int/news-room/fact-sheets/detail/sexually-transmitted-infections-(stis) (Accessed: 24 June 2024).
4. British Medical Journal (2024) Sexually transmitted infections: clinical features, diagnosis, and management. Available at: https://www.bmj.com/content/350/bmj.g5956 (Accessed: 24 June 2024).

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