The study intends to test the hypothesis that ME/CFS cases and controls have different bacterial, fungal or viral microflora in the oropharynx (mouth and throat regions), lower gastrointestinal tract (gut) and blood in a massive, well-powered study. By rigorously characterizing cases and controls and using state-of-the-art methods for identifying microbes, even currently-unknown ones, the CII will also study patients and controls for evidence of differences in immune system function and metabolic function