STI Risk Reference
About

STI risk reference

Compare published STI prevalence and per-encounter transmission risk across countries and sexual activities.

You
Hep B vaccinated (~75% in this country)
with
Partner
Hep B vaccinated (~75% in this country)
No condom
Unprotected — higher transmission rates shown.
Risks to you per sexual encounter

Hover any value for the breakdown.

Advanced

ActivityChlamydiaGonorrheaSyphilisHIVHepatitis BHepatitis C
Vaginal sex— you are insertive
Penis-in-vagina intercourse.
0.05%
0.06%
0.01%
0.0004%
N/A
0.001%
Anal sex— you penetrate
Penis-in-anus intercourse.
0.05%
0.005%
0.02%
0.0006%
N/A
0.007%
Blowjob (fellatio)— you receive
Oral sex on a penis.
0.009%
0.14%
0.007%
<0.0001%
N/A
negligible
Cunnilingus— you give
Oral sex on a vulva.
0.009%
0.003%
0.007%
negligible
N/A
negligible
Grinding
Unclothed genital-to-genital contact without penetration.
negligible
negligible
0.003%
negligible
N/A
negligible
Fingering
Manual stimulation of genitals or anus.
0.001%
0.0002%
0.0007%
negligible
N/A
negligible
Numbers are illustrative — published averages × country prevalence, not a personal prediction.Hep B shows N/A when the person is vaccinated — toggle per-person in the form above.HIV is asymmetric — receptive partners face higher risk than insertive partners.

Serious injury in a car accident

per car trip
0.001%

Any cancer diagnosis (ages 20–40)

per year
0.08%

Pregnancy from one act of protected vaginal sex (condom, typical use)

per encounter · Condom reduces per-act pregnancy risk by ~87% at typical use.
0.50%

Pregnancy from one act of unprotected vaginal sex

per encounter · Varies hugely with cycle phase; higher mid-cycle, lower otherwise.
4.0%

Catching the flu

per year
8.0%

Physical/sexual violence by an intimate partner (women, the Netherlands)

lifetime · WHO 2021 estimates of intimate partner violence (lifetime, ages 15–49); country figures from national surveys where available.
25%
Time bases differ (per encounter, per trip, per year, lifetime). Use these as rough magnitude anchors, not direct comparisons. Numbers are order-of-magnitude estimates.

Formula
R=T×P×(1−V)R = T \times P \times (1 - V)

RR — risk per encounter of the susceptible person contracting the STI.

TT — per-act transmission rate (assuming the infectious partner has the STI), from peer-reviewed meta-analyses.

PP — country prevalence of the STI in the infectious partner's country of residence.

VV — 1 if the susceptible person is vaccinated against Hep B, 0 if not (Hep B only; V=0V = 0 for all other STIs).

Inputs for this view
P=NetherlandsVHepB=1 (vaccinated)no condomP = \text{Netherlands}\quad V_{\text{HepB}} = 1 \text{ (vaccinated)}\quad \text{no condom}
Country prevalence (P)(P) — Netherlands
STIPrevalenceSource
Chlamydia0.80% – 1.5%ecdc-sti-2023
Gonorrhea0.15% – 0.30%ecdc-sti-2023
Syphilis0.02% – 0.04%ecdc-sti-2023
HIV0.50%unaids-2024
Hepatitis B0.25%who-hbv-2024
Hepatitis C0.30% – 0.60%euro-hcv-sr-2019
Per-act transmission rates (T)(T) — resolved for you
Direction follows the susceptible person's anatomy and the activity. Condom column matches the current selection (no condom).
ActivityDirectionChlamydiaGonorrheaSyphilisHIVHepatitis BHepatitis C
VaginalFemale → Male
2.0% – 5.0%althaus-2012-chlamydia-per-act
20% – 30%fairley-2019-gonorrhea-per-act
30% – 60%cdc-syphilis-transmission
0.05% – 0.10%patel-2014-hiv-per-act
10% – 20%cdc-hbv-transmission
0.10% – 0.30%terrault-2013-hcv-sexual
AnalReceptive → Insertive
2.0% – 5.0%althaus-2012-chlamydia-per-act
2.0%fairley-2019-gonorrhea-per-act
50% – 60%cdc-syphilis-transmission
0.06% – 0.16%patel-2014-hiv-per-act
20% – 40%cdc-hbv-transmission
0.50% – 2.0%terrault-2013-hcv-sexual
BlowjobReceiver of blowjob at risk
0.50% – 1.0%althaus-2012-chlamydia-per-act
63%fairley-2019-gonorrhea-per-act
10% – 30%cdc-syphilis-transmission
0.01%patel-2014-hiv-per-act
1.0% – 3.0%cdc-hbv-transmission
negligible
CunnilingusGiver of cunnilingus at risk
0.50% – 1.0%althaus-2012-chlamydia-per-act
0.50% – 2.0%fairley-2019-gonorrhea-per-act
10% – 30%cdc-syphilis-transmission
negligible
1.0% – 3.0%cdc-hbv-transmission
negligible
GrindingSkin contactnegligiblenegligible
5.0% – 10%cdc-syphilis-transmission
negligiblenegligiblenegligible
FingeringManual contact
0.10%althaus-2012-chlamydia-per-act
0.10%fairley-2019-gonorrhea-per-act
1.0% – 3.0%cdc-syphilis-transmission
negligiblenegligiblenegligible
Worked example — gonorrhea, vaginal sex
R=20% – 30%⏟T×0.15% – 0.30%⏟P  ≈  0.06%R = \underbrace{\text{20\% – 30\%}}_{T} \times \underbrace{\text{0.15\% – 0.30\%}}_{P} \;\approx\; \text{0.06\%}

Citation IDs appear next to each per-act transmission rate in the "How is this calculated?" section.

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