Background So They Can Know (STCK) is a partner notification website developed from extensive formative research conducted with the target population and health care providers. STCK allows patients in the United States to send informative anonymous notification emails for curable STIs to their partners. STCK captures self-reported reasons for sending emails, a unique aspect of the website.

Methods Website metrics data were analysed for each unique user to determine geographic location and referral to the site. Information on the number of emails sent, for which STIs, and self-reported reasons for sending were collected from users who sent emails.

Results Launched in September 2012 without promotion, STCK has had 3,972 unique visitors. Most (77.5%) visitors have been from the United States, almost half from California (29.6%) and Washington DC (17.7%). Most (62.3%) first-time visitors found the website by typing its URL, 25.5% through Google, and less than 4% through any other single source. 30 visitors have sent anonymous emails to a total of 56 recipients. Most emails (76.9%) were sent for unknown reasons, 10.6% were sent by users to themselves, 8.9% to partners, 1.3% as misuse, and 1.3% to a friend who was thought to be at risk for STIs. Most emails (57.9%) were sent for more than one STI, 26.3% for chlamydia alone, and 15.8% for gonorrhoea alone.

Conclusion Without active promotion through clinics or online search optimization, very few visitors to STCK have used the website for anonymous partner notification or for misuse. Anonymous partner notification websites cannot assume that all emails sent through their service are for partner notification purposes. The uptake of STCK among clinic populations or following search engine optimization remains to be seen in the ongoing programme. Active promotion will be studied in the future.