A recent meta-analysis of the relevant literature by two (2) Australian authors , has reported there was a positive association between bacterial infection and Alzheimer’s disease (Maheshwari & Eslick, 2015). They add that further research into the role of bacterial infection is necessary.
What exactly is a meta-analysis and why would consider this type of research, you may ask!
Your answer is here: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3049418/
Maheshwari P, Eslick G. Bacterial infection and Alzheimer’s disease: a meta-analysis. Journal Of Alzheimer’s Disease: JAD [serial online]. January 1, 2015;43(3):957-966