How to distinguish between Alzheimers and AIDS

Mr. Daniel to the Doctor's office to collect his wife's test results.

Receptionist: "I'm sorry, sir, but there has been a bit of a mix-up and we have a problem. When we sent the samples from your wife to the lab, the samples from another Mrs. Daniel sent as well and we are now uncertain which one is your wife's. Frankly, that's either bad or terrible."

Mr. Daniel: "What do you mean?"

Receptionist: "Well, one Mrs. Daniel tested positive for Alzheimer disease and the other for AIDS. We cannot tell which is your wife."

Mr Daniel: "That's terrible! What am I supposed to do now?"

Receptionist: "The doctor recommends that you drop your wife off in the middle of town and if she finds her way home, don't have sex with her."