AIDS Or Alzheimer's?

The doctor says to a man "I'm sorry, sir, but the test results have come back a tad inconclusive. Your wife could have either AIDs or Alzheimer's. We're not sure which".

The man replies, "Oh my God! That's awful! What should I do?"

The doctor says, "Take her down into the city centre and leave her there. If she finds her way back, don't fuck her!"