IntimateHealth

Evidence-based sexual health education

Sexually Transmitted Infections

Symptoms, transmission rates, testing windows, and treatment for every major STI. Clinically-sourced data from CDC, WHO, and peer-reviewed research.

Categories: All, Bacterial, Viral, Parasitic

HIV/AIDS

Pathogen: Human Immunodeficiency Virus (retrovirus) | Category: Viral | Curable: No

Prevalence: ~1.2 million living with HIV in the US; 39.9 million globally

Incubation: 2-4 weeks (acute symptoms); seroconversion: 2-12 weeks

Transmission

  • receptive Anal: 1.38% per act
  • insertive Anal: 0.11% per act
  • receptive Vaginal: 0.08% per act
  • insertive Vaginal: 0.04% per act
  • oral Sex: 0-0.04% per act
  • sharing needles: 0.63% per sharing
  • notes: Acute infection: 9.2x higher. Genital ulcers: 5.3x multiplier. U=U: 0% when virally suppressed.

Symptoms

  • acute: Fever, rash, sore throat, swollen lymph nodes, fatigue (2-4 weeks post-exposure)
  • chronic: May be asymptomatic for years. Without treatment: opportunistic infections, weight loss, neurological decline
  • aids: CD4 count <200: opportunistic infections (PCP pneumonia, toxoplasmosis, Kaposi sarcoma)

Treatment

  • standard: Antiretroviral therapy (ART) — typically 2-3 drug regimen. Biktarvy, Triumeq, or Dovato as first-line. Lifelong treatment.
  • outcome: With ART: near-normal lifespan. Viral suppression makes transmission impossible (U=U).

Chlamydia

Pathogen: Chlamydia trachomatis (bacterium) | Category: Bacterial | Curable: Yes

Prevalence: 1.8 million reported cases/year in US (most common bacterial STI)

Incubation: 7-21 days (often asymptomatic)

Transmission

  • per Act: 4.5-15% per unprotected vaginal sex act
  • routes: Vaginal, anal, oral sex. Can infect throat, rectum. Mother-to-infant during birth.

Symptoms

  • female: Often none (70% asymptomatic). Abnormal discharge, burning urination, bleeding between periods.
  • male: Often none (50% asymptomatic). Urethral discharge, burning urination, testicular pain.
  • rectal: Discharge, bleeding, pain.

Treatment

  • standard: Doxycycline 100mg twice daily for 7 days (preferred). Alternative: Azithromycin 1g single dose.
  • outcome: 95-97% cure rate. Reinfection common — retest in 3 months.

Gonorrhea

Pathogen: Neisseria gonorrhoeae (bacterium) | Category: Bacterial | Curable: Yes

Prevalence: 648,000+ reported cases/year in US

Incubation: 1-14 days (usually 2-5 days)

Transmission

  • male To Female: 60-90% per vaginal act
  • female To Male: ~20% per vaginal act
  • receptive Anal: ~84% per act
  • insertive Anal: ~2% per act
  • routes: Vaginal, anal, oral sex. Can infect throat, eyes. Mother-to-infant.

Symptoms

  • female: Often asymptomatic (50%). Discharge, painful urination, bleeding between periods.
  • male: Usually symptomatic (90%). Purulent urethral discharge, painful urination, testicular swelling.
  • pharyngeal: Usually asymptomatic sore throat.
  • rectal: Discharge, soreness, bleeding.

Treatment

  • standard: Ceftriaxone 500mg IM single dose (1g if >150kg). Dual therapy no longer standard since 2020.
  • resistance: CRITICAL CONCERN: Increasing resistance to ceftriaxone reported globally. "Super gonorrhea" strains emerging. WHO priority pathogen.
  • outcome: Current regimen >95% effective, but resistance is rising.

Syphilis

Pathogen: Treponema pallidum (spirochete bacterium) | Category: Bacterial | Curable: Yes

Prevalence: 207,000+ cases in US (2023) — dramatic increase since 2000. Congenital syphilis cases tripled.

Incubation: 10-90 days (average 21 days)

Transmission

  • per Act: ~2% per act (primary stage with chancre)
  • routes: Direct contact with syphilis sore (chancre) during vaginal, anal, oral sex. Mother-to-fetus (congenital).

Symptoms

  • primary: Painless chancre (ulcer) at infection site. Lasts 3-6 weeks, heals without treatment.
  • secondary: Rash (palms, soles), mucous patches, condylomata lata, fever, lymphadenopathy. 4-10 weeks after chancre.
  • latent: No symptoms. Can last years.
  • tertiary: Gummas (granulomas), cardiovascular syphilis (aortitis), neurosyphilis (dementia, tabes dorsalis). 15-30 years after infection.

Treatment

  • primary: Benzathine penicillin G 2.4M units IM, single dose
  • late: Benzathine penicillin G 2.4M units IM weekly x 3 weeks
  • neurosyphilis: Aqueous penicillin G IV for 10-14 days
  • alternative: Doxycycline for penicillin-allergic (not in pregnancy)
  • jarisch Herxheimer: Possible reaction within 24 hours of treatment — fever, chills, worsening rash. Self-limited.

Herpes (HSV-1 & HSV-2)

Pathogen: Herpes Simplex Virus Type 1 and Type 2 | Category: Viral | Curable: No

Prevalence: HSV-1: 67% of world population <50 (3.7 billion). HSV-2: ~13% worldwide (491 million aged 15-49).

Incubation: 2-12 days

Transmission

  • per Act: ~0.1% per act (HSV-2, asymptomatic shedding). Higher during outbreaks.
  • annual Risk: 5-10% per year in discordant couples without antivirals
  • reduced By: Daily antivirals reduce transmission ~50%. Condoms reduce ~30%. Combined: ~75% reduction.
  • notes: HSV-1 increasingly causes genital herpes (via oral sex). Shedding occurs without visible sores.

Symptoms

  • primary: Painful vesicles/ulcers in genital or oral area. Fever, body aches, swollen lymph nodes. Worst outbreak.
  • recurrent: Milder outbreaks. Average 4-5/year for HSV-2, 1/year for genital HSV-1. Decrease over time.
  • prodrome: Tingling, itching, or pain before lesions appear.

Treatment

  • episodic: Valacyclovir 1g BID x 10 days (first episode); 500mg BID x 3 days (recurrence)
  • suppressive: Valacyclovir 500mg-1g daily (reduces outbreaks 70-80%, reduces transmission ~50%)
  • alternatives: Acyclovir, famciclovir

HPV (Human Papillomavirus)

Pathogen: Human Papillomavirus (200+ types; 14 high-risk) | Category: Viral | Curable: No

Prevalence: Most common STI globally. ~80% of sexually active people infected at some point. 42.5 million infected in US.

Incubation: Weeks to months (warts); years to decades (cancer)

Transmission

  • per Act: Very high — skin-to-skin contact in genital area. Condoms reduce but don't eliminate risk.
  • routes: Vaginal, anal, oral sex, skin-to-skin genital contact. Can transmit without penetration.

Symptoms

  • low Risk: Types 6, 11: genital warts (condylomata acuminata). Not cancer-causing.
  • high Risk: Types 16, 18 (cause 70% of cervical cancers): usually no symptoms until precancer/cancer develops.
  • cancers: Cervical, anal, oropharyngeal, penile, vulvar, vaginal cancers.

Treatment

  • warts: Cryotherapy, imiquimod cream, podophyllin, surgical removal. May recur.
  • precancer: LEEP, conization, ablation for cervical dysplasia.
  • cancer: Surgery, radiation, chemotherapy depending on stage.
  • virus: No treatment for the virus itself — body clears most infections.

Trichomoniasis

Pathogen: Trichomonas vaginalis (protozoan parasite) | Category: Parasitic | Curable: Yes

Prevalence: 2.6 million infections in US (most common curable STI in young women)

Incubation: 5-28 days

Transmission

  • routes: Penile-vaginal sex primarily. Rarely vulva-to-vulva. Not from oral/anal sex, toilet seats, or swimming pools.

Symptoms

  • female: Frothy green-yellow vaginal discharge with strong odor, itching, burning, painful urination, dyspareunia.
  • male: Usually asymptomatic. Mild urethral discharge or irritation, post-ejaculation discomfort.

Treatment

  • standard: Metronidazole 500mg BID for 7 days (preferred). Alternative: Tinidazole 2g single dose.
  • notes: Avoid alcohol during treatment and 72 hours after (disulfiram reaction). Retest in 3 months.

Mycoplasma genitalium

Pathogen: Mycoplasma genitalium (bacterium) | Category: Bacterial | Curable: Yes

Prevalence: 1-2% of general population; 10-30% of men with non-gonococcal urethritis

Incubation: 1-5 weeks

Transmission

  • routes: Vaginal and anal sex. Possibly oral sex.

Symptoms

  • female: Vaginal discharge, bleeding between periods, pelvic pain. Often asymptomatic.
  • male: Urethral discharge, burning urination. Often asymptomatic.

Treatment

  • standard: If macrolide-sensitive: Doxycycline 100mg BID x 7 days → Azithromycin 1g day 1, 500mg days 2-4. If resistant: Doxycycline → Moxifloxacin 400mg daily x 7 days.
  • resistance: Macrolide resistance: 40-80% globally. Treatment-resistant cases increasing.

Hepatitis B

Pathogen: Hepatitis B Virus (HBV) | Category: Viral | Curable: No

Prevalence: ~880,000 chronically infected in US; 296 million globally

Incubation: 6 weeks to 6 months (average 90 days)

Transmission

  • routes: Blood, semen, vaginal fluids. Sexual contact, shared needles, mother-to-child. 50-100x more infectious than HIV.

Symptoms

  • acute: Fatigue, nausea, abdominal pain, jaundice (yellowing), dark urine. 30-50% of adults are symptomatic.
  • chronic: Often asymptomatic for decades. Can develop cirrhosis and liver cancer.

Treatment

  • acute: Supportive care. 95% of adults clear infection spontaneously.
  • chronic: Antiviral therapy (tenofovir, entecavir). Cannot cure but suppresses virus.
  • functional Cure: Research ongoing for functional cure (HBsAg loss).

Molluscum Contagiosum

Pathogen: Molluscum contagiosum virus (poxvirus) | Category: Viral | Curable: Yes

Prevalence: Common in children (non-sexual). In adults, genital molluscum is sexually transmitted.

Incubation: 2-7 weeks (up to 6 months)

Transmission

  • routes: Direct skin-to-skin contact. Auto-inoculation (spreading to new areas by touching). Fomites (towels, razors).

Symptoms

  • description: Small (2-5mm), flesh-colored, dome-shaped papules with central dimple (umbilication). Usually painless.

Treatment

  • standard: Self-resolving in 6-12 months. Faster: cryotherapy, curettage, cantharidin, imiquimod.