Test2Know: An online home-based self-sampling platform to test for HIV and other Sexually Transmitted Infections: Results of the pilot effectiveness phase (phase C)

Test2Know (T2K) is an online postal self-sampling service to test for HIV and other sexually transmitted infections (STI), developed by the Institute of Tropical Medicine Antwerp to provide low-threshold, home-based testing for asymptomatic individuals at behavioural risk. Users complete an online questionnaire on their sexual behaviour during the previous six months. Based on a risk-based algorithm, a personalised test kit is generated in line with testing guidelines. As a result, not all users are tested for all infections. Users pay a fixed fee of 30€, irrespective of the number or type of tests requested. When a test result is positive, users are proactively contacted to facilitate linkage to care.

This report presents the results of the pilot effectiveness phase (Phase C), conducted between February and September 2025. During this phase, 538 test kits were shipped to 532 individuals, mainly across Flanders, and 390 kits were returned, corresponding to a return rate of 72.5%. One third of users who returned a kit reported never having been tested for HIV or another STI before (33.6%).

Importantly, among first-time testers, 9.2% (12/131) were positive for an STI. This is an important finding, as one of the main potential public health benefits of online self-sampling is its ability to lower barriers to testing and reach individuals who do not access traditional services. In total, 28 STIs were diagnosed: 19 chlamydia infections, one gonorrhoea infection and eight active syphilis infections. No HIV or hepatitis C infections were detected. Overall STI positivity was 7.1% among all returned kits and 8.5% among kits that could be fully processed.

Partner notification emerged as a particularly relevant testing pathway, with markedly higher STI positivity among users who ordered a kit following partner notification (9/35; 25.7%). STI positivity was also higher among men who have sex exclusively with men (MSM), and all active syphilis infections were diagnosed in this group, supporting the continued relevance of targeted syphilis testing among MSM. Importantly, compared with a universal testing approach, the personalised testing algorithm avoided a substantial number of Chlamydia trachomatis/Neisseria gonorrhoeae PCR tests (16%) and syphilis serology tests (56.4%). This risk-based approach may contribute to a more efficient use of laboratory capacity and public health resources, particularly in a context of increasing budgetary constraints.

User satisfaction was high, with an average score of 87.2%. Most respondents preferred fully home-based testing (99/142; 69.7%) or a hybrid model combining home sampling with healthcare professional support (40/142; 28.2%). The main operational limitation was incomplete processing due to insufficient blood volume, highlighting the need for further optimisation of blood self-sampling.

Overall, this pilot phase demonstrates that T2K is a feasible, acceptable and effective complementary HIV/STI testing strategy in Belgium. The findings support further evaluation of T2K’s reach, cost, complementarity with first-line care, and potential integration into routine HIV/STI testing and partner notification pathways.