I mean, we know about all kinds of microbes that can be in the brains of "unhealthy" people, and we've known that for ages (taxoplasmosis and CJD come to mind).

I mean, we know about all kinds of microbes that can be in the brains of "unhealthy" people, and we've known that for ages (taxoplasmosis and CJD come to mind). The association in the article isn't a case of "we didn't find it in healthy people", but "we found it in more in unhealthy people". From the article: "It found that, while there was a remarkable diversity of species in the control brains, there were often overgrowths of certain bugs in Alzheimer’s brains."