I'm glad to know you and your partner discussed your HIV/STI situation before the event. All things considered, probably you are at little or no risk.

No data exist on STI risks from analingus. However, we know that cunnilingus rarely transmits any STI. Probably the most common risk for the anal partner in analingus is gonorrhea, but almost certainly even that is rare. In theory herpes due to HSV1 and syphilis might be risks, although I've never seen nor heard of such a case. HIV is almost never transmitted by saliva or by any oral sexual exposure. You also describe a partner unlikely to have any oral and transmissible infection. (The major health risk from analingus is for the oral partner, for gastrointestinal infections but little risk for STIs.) I would not advise you be tested for anything.

I hope this information is a little bit helpful. Let me know if anything isn't clear.

HHH, MD