Pathogens that cause STI

• Virus: HIV, Hepatitis, HPV, HSV

• Bacteria: Neisseria gonorrhoea, chlamydia trachomatous, treponema pallidum

• Fungi: candida albicans

• Protozoa: trichomonas vaginalis

• Parasite: crab louse "crabs", pubic lice (Pthirus), scabies

8 pathogens linked to greatest incidence of STI

• Virus (MSV, HPV, HIV, Hepatitis B), bacteria (chlamydia, gonorrhoea, syphilis), protozoa (trichomonas)

4 important curable STIs

• >1 million infections/day: Trichomonas (156 million/yr), chlamydia (127 million/yr), gonorrhoea (87 million/yr), syphilis (6 million/yr)

• Higher incidence in low-income compared with high-income economies (demographic factors, polygamy, commercial sex work, inadequate medical services)

4 global WHO targets

• Syphilis, congenital syphilis, HPV, gonorrhoea

Consequences of STI's

• Fetal and neonatal deaths: Syphilis in pregnancy (>350,000 adverse birth outcomes/year)

• Cervical cancer: HPV infection (>500,000 cases and >250,000 deaths)

• Infertility: gonorrhoea, chlamydia

• HIV risk: presence of STIs like syphilis, HSV, gonorrhoea increase risk of acquiring or transmission HIV by 2-3x

• Physical, psychological, & social consequences can compromise quality of life

Epidemiological model for STI transmission

Considerations

• No significant non-human reservoirs

• Role of sexually active groups and human behavior (sexual, healthcare seeking)

• R0 (basic reproduction number) = B * C * D

  • B: transmission coefficient/transmissibility per contact. E.g. higher for anal sex compared with vaginal sex for HIV. Interventions include condoms, safer sex practices, control of STIs to reduce HIV transmission

  • C: mean rate of partner change. Sexual networks are important (core groups, bridging populations, general population), average #of partners

  • D: duration of infectiousness. Depends on availability of testing (including asymptomatic) and treatment

STI's & HIV

• Strong evidence that presence of STIs (ulcer and discharge) in HIV positive individuals increases transmission to HIV negative

• Presence of STI in HIV negative may increase risk of HIV acquisition (strong evidence for ulcers, weaker evidence for discharge)

• Risk of STI transmission if immunosuppressed??

Presentations

Genital ulcer

Top 3:

• HSV 2: (self-limiting (few days), vesicles (increased since 1990)

• Primary Syphilis: usually painless, solitary chancre

• Chancroid: often multiple and painful +/- lymphadenopathy/buboes (was #1 pre-1990)

Less common:

• Granuloma inguinale/donovonosis

• Lymphogranuloma venereum (LGV)

Clinical diagnosis unreliable. Management depends on setting and available of tests, or syndromic management

Urethral discharge (male)

• Chlamydia

• Gonorrhoea

• Trichomonas

Vaginal discharge

• Chlamydia

• Gonorrhoea

• Trichomonas

• Mycoplasma genitalium

• Candida

• Bacterial vaginosis

Inguinal swelling

• Chancroid

• Syphilis

• LGV

Scrotal swelling (epididymitis) / infertility (men)

• Chlamydia

• Gonorrhoea

Neonatal conjunctivitis

• Gonorrhoea

• Chlamydia

Warts/carcinoma (cervix/rectum)

• HPV

Others: hepatitis, fever etc.

• HIV, hepatitis B, 2/3 syphilis

Syndromic management

• Use of treatment algorithms to cure common causes of defined clinical syndromes

• Useful where there is a high STI burden without advanced diagnostics

• Assumes strong correlation between syndromes and a particular disease

• Available for urethral discharge, vaginal discharge, genital ulcers, inguinal swelling, scrotal swelling, lower abdominal pain in women, neonatal conjunctivitis

• Advantages: simple, cheap,

• Disadvantages: