To begin, the term 'sepsis' refers to a severe, life-threatening infection, typically from bacteria, that can cause low blood pressure and sometimes shock, typically requiring hospitalization and ICU admission. I recommend that you discuss your concern with your physician. When you ask what the odds of getting sepsis are, what you are asking is what are the odds of a) getting an infection, and b) having the infection be so severe that it causes a diffuse inflammatory response.
Having clarified that, in a normal, immunocompetent person, the odds of getting a severe, sepsis-causing infection from anal sex is very low. This does not apply to people who are immunocompromised, specifically people who have had transplants, are on chronic steroids, or who have HIV. If you have any immunocompromising condition I would strongly recommend that you refrain from further anal intercourse until discussing this with your doctor
All that being said, anal sex does put you at risk for certain infections. The most notable of these are all the STDs (HIV, hepatitis B, gonorrhea, chlamydia, etc), which are more likely to be transmitted via anal intercourse compared to vaginal intercourse. HPV can also be transmitted anally, which means that you should inform your physician if you have regular anal intercourse so they can determine whether you should have anal pap smears in addition to your regular cervical pap smears. There are also other infections that can be transmitted; specifically, the penetrating partner is at risk for urinary tract infections, and the person receiving anal intercourse is at risk for local infections such as an anal abscess
. These infections overall are rare, but in even more rare cases they could be severe enough to cause sepsis. Again, I would recommend that you schedule an appointment with your physician to discuss your questions and how you can be safe while enjoying a satisfying sex life.