Chlamydia pneumoniae, a form of walking pneumoniae, in its acute and chronic persisting form, has been implicated in dermatomyositis and polymyositis, in addition to a number of other rheumatic and autoimmune manifestations.
Acute Chlamydia pneumoniae infection in the pathogenesis of autoimmune diseases. Lupus. 2009 Feb;18(2):164-8. doi: 10.1177/0961203308096069.
A controlled study examining the frequency of chlamydia pneumoniae in the origin and development dermatomyositis/polymyositis, rheumatoid arthritis, systemic lupus erythematosus, myeloperoxidase-antineutrophil cytoplasmic autoantibody (MPO-ANCA)-associated vasculitis, adult onset of Still’s disease and giant cell arteritis/Takayasu arteritis. Authors suggest there is a strong statistical probability that this infection has significant involvement in autoimmune pathogenesis.