The possibility of an infectious etiology for Alzheimer's disease (AD) has been repeatedly postulated over the past three decades. We provide the first meta-analysis to address the relationship between bacterial infection and AD. Studies examining the association between AD and spirochetal bacteria or Chlamydophila pneumoniae (Cpn) were identified through a systematic search of the databases MEDLINE, EMBASE, PubMed, and Google Scholar. Data combined from 25 relevant, primarily case-control studies demonstrated a statistically significant association between AD and detectable evidence of infection of either bacterial group. We found over a ten-fold increased occurrence of AD when there is detectable evidence of spirochetal infection (OR: 10.61; 95% CI: 3.38-33.29) and over a four-fold increased occurrence of AD in a conservative risk estimate (OR: 4.45; 95% CI: 2.33-8.52). We found over a five-fold increased occurrence of AD with Cpn infection (OR: 5.66; 95% CI: 1.83-17.51). This study shows a strongly positive association between bacterial infection and AD. Further detailed investigation of the role of bacterial infection is warranted.