Chlamydia pneumoniae—a common bacterium that causes pneumonia and sinus infections—can linger in the eye and brain for years and may aggravate Alzheimer's disease, according to a study. The discovery suggests this bacterium can amplify Alzheimer's disease and points to potential interventions including inflammation-limiting therapies and early antibiotic treatment. The study shows for the first time that Chlamydia pneumoniae can reach the retina—the tissue lining the back of the eye—where it triggers immune responses linked to inflammation, nerve cell death and cognitive decline. "Seeing Chlamydia pneumoniae consistently across human tissues, cell cultures and animal models allowed us to identify a previously...