Create an anonymous email account that can't get you identified and email the clients with a note that you visited me within the past 3, 4, 5, 6 months etc. I recommend a hushmail account.
I would like to inform you that I recently undertook a routine STD test and regretfully tested positive for gonorrhea. I recommend you visit a medical provider as soon as possible for an STD test and another one three months from now to confirm you are negative.
You can also get a prepaid phone and have it registered anonymously and text a notice at risk clients. Do not call or answer the phone, clients could recognize your voice.
Another option is to create another TER account that can't be traced to you or your aliases and post a notice on your home board. You would also be able to answer any questions anonymously.
Doing all three options covers all bases and helps the word get out to as many at risk clients as possible.
The one problem might be if a client has only seen you in the date range you give like three months, you could be identified if the client has only seen one provider.
Clap while still curable is beginning to be a problem again as several strains of the disease have become resistive to standard treatment.
You might also ask the clinic or medical provider where you got tested if they can notify "sexual partners" on your behalf that a partner has tested positive and encourage those at risk to get tested. This should only be done if they can do so and provide anonymity for you