Hi there Muffn. For the record, allow me to say that i believe both you & your husband when you say you have been faithful. Also please note that these tests' are not foolproof as no doubt your treating doctor will have informed you. So in effect, you may not have had a chlamydial infection at all. Having said that, allow me to quell the thought that 'anal' sex contributed to the infection. Chlamydia may on occasion be contracted through direct contact not sexually related. Sexual contact of any sort may be contributory, not just anal sex. I hope these clarifications suffice. More inmportantly, hope you follow the entire treatment package for BOTH partners as advocated by your doctor. Regds & wish you a speedy recovery. Dr Praveen Rodrigues MD Dermatologist & venereologist, Bangalore, India