Condoms provide really good protection from most serious STI’s (like HIV, gonorrhea and chlamydia) so it’s great you were using one. It can be worrisome to get other people’s blood on you, but blood and body fluids don’t usually pass on STI’s unless they enter an opening in your body (like the hole a the tip of your penis). From what you described here, you didn’t get any blood or body fluids into an opening in your skin.
The things that condoms are less able to prevent are the kinds of infections that pass from skin-to-skin contact. This can happen any time you have sex, whether or not there is menstrual blood present, just from the skin that touches around the base of the condom. Condoms offer some protection against these infections, but infection can still happen. STI’s that pass this way are genital warts, herpes, and syphilis.
It’s hard to say how severe the risk is. This depends on if your partner had any STI’s at the time you had sex. I don’t think you’re at any more risk from this incident than you would be as a sexually active person, but it’s a good idea for anyone sexually active to get tested regularly. Syphilis testing is offered as part of regular STI testing in BC, and the best time to test is about 1-3 months after you might have been exposed. We diagnose herpes and warts based on your symptoms, so if you notice any bumps or sores on your genitals, then come in for an exam at that time.
Hope that helps,