Sexually-transmitted infections

Definition

• infections that are commonly transmitted by sexual activity
  • vaginal sex
  • anal sex
  • oral sex

Pathogen and disease

syphilis

• Treponema pallidum
  • one of 3 major spirochaetes - leptospirosis and borrelia
• 6 mil. new cases/2018
• higher in female sex worker and MSM
• diagnosis
  • non-treponemal - positive during active stage; sensitive, not specific
    • VDRL
    • RPR
  • treponemal - positive for lifelong; specific, not sensitive
    • TPHA
    • TPPA
    • FTA

	non-treponemal positive	non-treponemal negative
treponemal positive	active syphilis	past syphilis
treponemal negative	other active disease	nothing

• difficulty of microscopy - endemic treponematoses
  • T. pallidum - Syphilis
  • T. ssp pertenue - Yaws
  • T. pallidum spp. endemicum - Bejel
  • T. carateum - Pinta
• morphologically identical and serologically indistinguishable

Epidemiology

• Syphilis in pregnancy > 350,000/year adverse birth outcome
• Cervical cancer due to HPV
• Infertility due to gonorrhea and chlamydia
• HIV, needless to say

• considerations
  • no significant non-human reservoirs
  • role of sexually active groups
  • highlye dependent upon human behavior

[math]\displaystyle{ R_0 = B \times C \times D }[/math]

• [math]\displaystyle{ B }[/math]: transmission coefficient
• [math]\displaystyle{ C }[/math]: mean rate of partner change
• [math]\displaystyle{ D }[/math]: mean duration of infectiousness

• mode of propagation
  • core groups ⇄ bridging population ⇄ general population
  • size of each group differs among different countries

Presentations

genital ulcer

• herpes simplex
• syphilis
• chancroid
• donovanosis
• LGV
• undetermined

urethral discharge

• vaginal discharge
• inguinal swelling
• scrotal swelling
• lower abdominal pain
• neonatal conjunctivitis
• warts/carcinoma
• hepatitis
• fever

Treatment

• WHO has published Tx guidelines for each of STIs
• syndromic management algorithms, e.g. by MSF, are more effective in high STI burden situation without advanced diagnostics
  • disadvantages of over treatment
    • e.g. using penicillin, azithromycin and aciclovir for genital ulcer (against each of syiphilis, chancroid and HSV)
  • disadvantages for women
    • problems with partner notification; stigmatization
    • only symptomatic STIs treated