Quantifies how much each day added, with the underlying encounters.
Made for gay and bisexual men
Turn uncertainty into a measured estimate.
SixtyNineMSM models your encounters into a personalised, quantitative estimate of your STI risk: the probability that you have acquired at least one infection since your last test. Each estimate is calibrated against UK surveillance data and computed entirely on your device — no account, no server, nothing leaving your iPhone.
- A quantified probability, per infection
- The factors driving your estimate
- Evidence-based decisions between tests
The clinical question "Probability of infection?"
Computed from your history and published transmission data.
Private Stays on your phone
No account, no server. The developer never sees your data.
All major STIs Built on UKHSA & published data Accounts for PrEP & condoms On-device, no account
A test measures a single point in time. Risk accumulates continuously.
Between tests, individual encounters combine in ways that resist intuition. A single high-anxiety encounter may carry modest risk; a routine one may contribute disproportionately. Protection, PrEP adherence, vaccination status, sexual role and partner serostatus each alter the underlying probability. SixtyNineMSM integrates these variables into one coherent estimate rather than leaving them to guesswork.
Your risk
Quantify the risk you are actually carrying.
SixtyNineMSM estimates the cumulative probability that you have acquired at least one STI since your most recent negative test, derived from every encounter you record.
Where you stand
A calibrated probability, infection by infection.
Sexual-health risk is continuous, not categorical. SixtyNineMSM reports a single overall probability, a separate estimate for each infection, and a 95% credible interval that quantifies the uncertainty in every figure.
- Cumulative probability of acquiring any covered STI
- Individual estimates for HIV, gonorrhoea, chlamydia and syphilis
- A 95% credible interval accompanying every estimate
Understand it Daily contribution Per-infection trajectory
Attribute your risk to its sources.
A single percentage is more informative when its components are visible. SixtyNineMSM decomposes your estimate by day, by encounter and by infection, distinguishing the events that materially changed your risk from those that did not.
Tracks each infection's probability independently over time.
Prevention that counts
Quantify the effect of protection.
Condoms, PrEP, vaccination and partner viral suppression each modify the per-act transmission probability. SixtyNineMSM applies these factors to every encounter and reflects their effect in the resulting estimate, making the contribution of each intervention measurable.
- Condom use applied per relevant act
- PrEP coverage inferred from Apple Health dose history
- Partner HIV status, treatment and viral suppression
- Vaccination status (HepB, HPV, Mpox)
Beyond yourself
Assess your risk before a new encounter.
Sexual-health decisions are not made in isolation. SixtyNineMSM quantifies the likelihood that you are currently carrying an infection when considering a new or existing partner. It does not predict transmission, but it replaces assumption with a defensible estimate — informing your own decisions about protection, disclosure and the contact you are comfortable with.
How it works
From recorded encounter to quantified risk.
Record an encounter
Log the encounter, the protection used and the available information about your partner. The record remains on your device.
Recompute the estimate
Your cumulative probability updates immediately, showing the contribution and direction of each encounter.
Maintain the baseline
Continue recording between scheduled tests. Entering a result re-anchors the estimate to the appropriate baseline.
Between tests
A continuous estimate between tests.
A negative test establishes a new baseline. SixtyNineMSM then models risk accumulation from that point, encounter by encounter, until your next result. It does not replace scheduled testing or clinical advice; it quantifies the interval between them.
- Risk anchored to your most recent test
- Results and treatment retained in a private history
- Baseline reset after a negative result or completed treatment
Why you can trust it
Grounded in surveillance data.
SixtyNineMSM combines published per-act transmission probabilities with infection prevalence from UK surveillance data, adjusts them for the circumstances of each encounter, and propagates uncertainty through to the final estimate using a Bayesian model. Every assumption and source is documented in the app.
- Calibrated to published UK surveillance and research
- Adjusted for the circumstances of each encounter
- Bayesian propagation of uncertainty
- Assumptions and sources documented in-app
Your privacy
Computed entirely on-device.
This is among the most sensitive data a person holds, and it is treated accordingly. SixtyNineMSM operates with no account, no analytics and no server. All computation occurs locally; records are encrypted at rest and remain under your control. The developer cannot access your data, because the application transmits nothing.
The app has no account and no backend, and never connects to the internet. There is nowhere for your data to be sent, so the developer and any third party simply never get it.
Your data lives in an on-device database, encrypted at rest while your phone is locked and excluded from iCloud and device backups. Exports are password-protected and unlocked with Face ID.
If you turn it on, the app reads your PrEP doses and can write encounters to Apple Health as "Sexual Activity". Anything in Apple Health is then managed by Apple and may sync via iCloud per your iOS settings. Leave it off and nothing is written there.
Not medical advice.
SixtyNineMSM provides statistical estimates for educational and informational purposes only. It is not medical advice, not a diagnosis, and cannot detect, confirm, or rule out any infection. Always consult a qualified healthcare professional and get tested.
FAQ
The questions you're probably asking.
Where do the numbers come from?
Each encounter carries a per-act transmission probability drawn from published UK surveillance data. SixtyNineMSM aggregates these across every encounter since your last test, adjusts for the protection recorded, and uses a Bayesian model to fill gaps and quantify the uncertainty in the result.
Does it work outside the UK?
The baseline infection rates come from England (UKHSA and ONS data), so the estimates are calibrated for that population. You can record encounters anywhere, but the further your setting is from that epidemiological context, the less precise the estimates become.
What if I don't know a partner's status?
That is the expected case, and the model accounts for it. When serostatus, viral suppression or PrEP use is unknown, SixtyNineMSM applies the prevalence rates for that characteristic across the relevant population, rather than assuming best or worst case.
Which infections does it cover?
HIV, gonorrhoea, chlamydia and syphilis. HepB, HPV and Mpox vaccination status is also recorded and factored in where it modifies the per-act transmission probability.
How accurate is it?
It is an estimate, not a diagnostic result. It applies population infection rates to what you record, so its accuracy depends on the completeness of your data. The 95% credible interval beside each figure states the uncertainty explicitly.
Who can see my data?
Only you. The app has no account and never connects to the internet, so the developer receives nothing. Your data sits in an encrypted database on your device, excluded from iCloud and device backups.
What about the Apple Health sync?
It is optional and off by default. When enabled, the app reads your PrEP dose history and writes encounters to Apple Health as "Sexual Activity" samples. Data in Apple Health is managed by Apple and may sync to your other devices via iCloud, depending on your iOS settings — outside the app's control. Leave it off and nothing is written to Health.
Does it replace testing?
No. It provides statistical estimates for informational purposes and cannot diagnose or exclude any infection. Continue testing on your scheduled interval and consult a healthcare professional with any concerns.
Almost here
Replace "probably" with a probability.
Quantify the likelihood that you have acquired an STI, understand the factors behind it, and inform your decisions with evidence. SixtyNineMSM is coming soon to the App Store.
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