As far as I know it's not been scientifically proven (yet) that a link b/w certain stealth infections and AD exists. However there is scientific evidence that certain infections (eg Lyme, Chlamydia pneumonia, Mycoplasma, HHV-6) can cause neurological damage or illnesses.
They are called stealth infections because they won't show up on standard blood tests, as these bugs tend to hide away in various body tissues, eg. heart, liver, blood vessels, nervous system and even white blood cells, totally unchecked by the immune system and causing damage which cumulate over the years.
The problems are two: a)most doctors are ignorant of this and (b) there are few places in the uk where one can have proper tests to check whether one carries these bugs, even though one may be/feel asymptomatic (can only think of a couple of doctors).
It may not be the case for evryone but getting checked out for any of such bugs, at least in my experience, may be worthwhile and quite revealing.
For those interested in this topic here's a few references:
video by prof T Marshall at the 2008 world gene congress.
technical but gives an idea of how bacteria affect human dna, metabolism and health.
article by prof Garth Nicolson on infections and neurodegenerative diseases
http://www.immed.org/NeuroDiseases/neur ... ne0508.pdf
helpful site specifically about Chlamydia pneumonia
prof T marshall website