Sexual health

The commonest bacterial STI in the UK, frequently asymptomatic. Causes urethritis, cervicitis and can ascend to PID; vertical transmission causes neonatal conjunctivitis and pneumonia.

Second commonest bacterial STI; purulent urethritis/cervicitis, with rising antimicrobial resistance driving the ceftriaxone-only first line and mandatory test of cure.

Multistage spirochaetal infection: primary (painless chancre), secondary (systemic rash incl. palms/soles, condylomata lata), latent, and tertiary (gummata, cardiovascular, neurosyphilis). "The great imitator."

An increasingly recognised cause of non-gonococcal urethritis and cervicitis, with rising macrolide resistance; tested for when symptoms persist after doxycycline.

Recurrent vesicular/ulcerative genital infection. First episode is the most severe (painful ulcers, systemic features); the virus then establishes latency in sensory ganglia with recurrences.

Benign epithelial growths from low-risk HPV (6/11). Distinct oncogenic types (16/18) drive cervical/anal/oropharyngeal cancer and are targeted by vaccination and screening.

Retroviral infection causing progressive CD4 depletion and immunodeficiency. Seroconversion → asymptomatic latency → AIDS-defining illness if untreated. Treatable to undetectable (U=U).

A blood-borne virus transmitted sexually, parenterally and vertically — one of the blood-borne viruses GUM screens for alongside HIV, hepatitis C and syphilis. Causes acute hepatitis; a proportion (higher if acquired perinatally) become chronic carriers at risk of cirrhosis and hepatocellular carcinoma. Vaccine-preventable.

Overgrowth of anaerobes replacing lactobacilli, raising vaginal pH. The commonest cause of abnormal discharge; not strictly an STI but linked to sexual activity. Important in pregnancy (preterm birth).

Common fungal vaginitis — itch and thick white discharge with a normal vaginal pH. Not an STI; precipitated by antibiotics, diabetes, pregnancy and immunosuppression.

A sexually transmitted protozoal infection causing vaginitis/urethritis. Notable for the frothy discharge and "strawberry cervix", and for raising HIV transmission risk.

Infection of the upper female genital tract (endometritis, salpingitis, tubo-ovarian abscess, peritonitis). Treated empirically and early to protect fertility; a low diagnostic threshold is recommended.

Inflammation of the epididymis ± testis. Aetiology is age-stratified — STI in younger men, enteric organisms in older men — which determines empirical therapy. The key emergency to exclude is testicular torsion.

An invasive form of chlamydia (serovars L1–3) that infects lymphatic tissue rather than just mucosa. In the UK it occurs almost exclusively in men who have sex with men, usually as a proctitis and often with HIV co-infection. The exam point: it needs 21 days of doxycycline, not 7.

Infestation of coarse body hair (pubic, but also axillary, chest, and eyelashes) by the crab louse, spread by close/sexual contact. Causes itch; managed with a topical insecticide and treated as an STI (full screen + partner treatment).

A bacterial cause of PAINFUL genital ulceration with suppurative inguinal lymphadenopathy, common in tropical/resource-limited settings and rare in the UK. The classic counterpoint to the painless syphilitic chancre in the genital-ulcer differential.

A common pox-viral skin infection causing small umbilicated papules. In children it is widespread and innocent; acquired sexually in adults it clusters in the genital/pubic area. Self-limiting in the immunocompetent; extensive/atypical lesions raise the question of HIV.

A sexually transmitted protozoal infection causing vaginitis and urethritis. It is the one "discharge" diagnosis that is unequivocally an STI, so partner notification and a full sexual health screen are part of treating it — which is what separates it from bacterial vaginosis and candidiasis in the exam.