Closing the gaps in STI partner notification.

Bacterial STIs are at record levels across Europe.

ECDC reports that confirmed cases of gonorrhoea, syphilis and chlamydia have all risen over the last decade, and its report for 2023 describes the highest gonorrhoea notification rate recorded since European reporting began in 2009.

Partner notification is a standard part of STI care, but it depends on a patient being able to name and reach their partners. After an anonymous encounter that is often not possible. That gap is what AfterCare is built for. It is our motivation, not a finding, and Section 04 says where we most need it tested.

• All confirmed cases
• Men who have sex with men

Gonorrhoea · 30,564 → 106,331

Syphilis · 21,585 → 45,577

Chlamydia · 168,239 → 213,443 · MSM series begins 2020

Show the data as a table

Confirmed cases reported to ECDC, EU/EEA, 2015–2024

Year	Gonorrhoea	Gonorrhoea (MSM)	Syphilis	Syphilis (MSM)	Chlamydia	Chlamydia (MSM)
2015	30,564	7,892	21,585	8,393	168,239	—
2016	37,046	10,184	23,032	9,209	174,979	—
2017	41,944	12,325	25,379	9,640	179,951	—
2018	40,224	13,450	25,078	9,637	164,523	—
2019	41,792	14,279	26,075	10,054	175,777	—
2020	40,051	14,569	23,290	9,501	161,969	7,226
2021	50,777	17,814	26,882	10,257	188,521	12,705
2022	75,065	25,588	35,707	13,901	219,978	15,067
2023	99,270	32,301	42,033	15,310	230,788	15,922
2024	106,331	32,918	45,577	15,539	213,443	14,998

Limits of these data

• Notifications, not incidence. Counts are confirmed cases reported by national authorities.
• Testing and reporting move the numbers too. Reporting countries are ECDC's EU/EEA aggregate.
• A signal of scale, not of effect. We read the trend as evidence the problem is large and growing, not as a measure of any intervention.

Notification without identification.

Two people who have been in close contact pair their halves of a card, by QR code or wristband. If either later tests positive, one tap tells the other, anonymously. No names, no accounts, no identifying information exchanged. The app is free, open source and built and hosted in Europe.

1. KeepEach person holds one half of a card pair.
2. ScanScanned in the app whenever they are ready.
3. ConnectedThe halves match once both have scanned.
4. NotifiedIf either tests positive, one tap tells the other. No identifying information is exchanged.
5. TreatedEarlier care, only when advised by healthcare professionals.

AfterCare does not diagnose, advise on treatment, or replace clinical care. Status: in development. Code: app · backend. How we protect users: privacy policy.

Measuring outcomes without identifying anyone.

Proposed design · open to critique

We would measure behaviour after a notice, not confirmed-case counts. Counts rise with testing, so they cannot show whether notification works. Everything below is a proposal for you to challenge, not a method we have already validated.

What we would measure

• Testing after a notice. The share of notified users who test, and the time from notice to test.
• Treatment started. Where a clinic can report it, in aggregate.
• Onward notification. Whether a notified user in turn notifies their own contacts.

How, with the least data

AfterCare has no accounts, so any measurement has to be opt-in, carry no identifier, and reveal nothing about one device that it does not reveal about all. Four techniques, each with its limit:

• Opt-in, event-level only A device sends a single yes/no event, such as “tested within 14 days of a notice”, only after explicit consent, and nothing else. self-selection: people who opt in may differ from those who do not.
• Local differential privacy Each device adds calibrated noise before sending, so no single report can be trusted, while the aggregate remains estimable. needs large samples; small countries or subgroups may fall below what is measurable at a privacy level we would accept.
• Secure aggregation The server receives only the sum across devices, never an individual contribution. protects against our own server, not against a biased sample.
• Clinic-side aggregate counts Partner clinics report counts of attendances that cite the app, with small cells suppressed, never linked to app data. depends on clinics asking the question consistently.

We have not named federated learning because it trains models, and we have no model to train. Federated analytics, which computes counts and histograms on the device, is the closer fit. Tell us if you disagree.

What we would need to settle first

• A comparison. A staggered rollout by region or clinic, so some areas serve as the comparison. Outcomes registered before launch.
• The privacy budget. The differential-privacy parameter (ε), set with a statistician and published.
• Consent and policy. Opt-in measurement changes what we tell users. It needs ethics review and an updated privacy policy before any data is collected.

Where we need people who know more than we do.

We are not a research institute, and we do not want to be judged as one. We publish only official figures, from ECDC and similar public health bodies, and no impact projections until clinicians have reviewed the assumptions behind them. We would like help with three things:

• Clinical soundness. Is the notification flow and its wording sound, and safe for the person receiving a notice?
• Defensible impact claims. What can be claimed, and is the measurement design above sound? Better notification drives testing, and testing finds cases, so confirmed counts may rise before they fall.
• Country-specific pathways. Which testing and treatment routes should the app point to in each country?

contact@after-care.eu

What we are relying on.

Every figure on this page comes from the first source below. The rest is the evidence we have read on partner notification and on the trend. If there is a study we should read, or one that contradicts us, please send it.

• ECDC Surveillance Atlas of Infectious Diseases European Centre for Disease Prevention and Control · data accessed September 2026

  Source of every number and chart above (confirmed cases, EU/EEA, gonorrhoea, syphilis and chlamydia). Reuse follows ECDC's intellectual property notices; the charts are our own drawings of the ECDC totals.

• Bacterial STIs reach record highs in Europe, congenital syphilis cases nearly double ECDC · news release

  ECDC's own summary of the trend shown in Figures 1 and 2.

• Gonorrhoea: Annual Epidemiological Report for 2023 ECDC · report (PDF)

  Country-level notification rates, population breakdown and methods. Its totals use ECDC's annual-report country set and differ slightly from the atlas aggregate used above.

• Strategies for partner notification for sexually transmitted infections, including HIV Ferreira, Young, Mathews, Zunza, Low · Cochrane Database of Systematic Reviews, 2013 · DOI 10.1002/14651858.CD002843.pub2

  Pooled 26 trials of partner-notification strategies. It found no single optimal strategy for any infection, and called for better trials on HIV and syphilis with biological outcomes. A newer version may exist; check the Cochrane Library.