My aunt is 84 and has a very bothersome rash on the back of her upper right arm. She got a flu shot on Oct. 31. On Nov. 9, she developed a red blotch approximately the size of a baseball that was very itchy, warm and sore. Her doctor initially thought it was a reaction to the flu shot. Shortly thereafter, the rash spread to her back and side, part of her left arm, as well as her ear (all with the same symptoms- red, itchy, hot). Her doctor prescribed Keflex (500mg) in case of cellulitis, which did not cure the problem. Today, her doctor claimed he did not know what the problem is and prescribed a steroid as well as an anti-itch pill. She works as a volunteer in a hospital gift shop, and also takes a low dose antibiotic regularly for chronic uti's. My question is, could the rash be caused by a resistant strain of bacteria that the Keflex would not have killed?