Unusual pathogens for respiratory infections.

: There are a large number of unusual pathogens for respiratory tract infections. The list of such pathogens is continuously changing because of changes in our environment, changes in the host (especially immunosuppression), and advances in medical technology, which allow minimally or otherwise nonpathogenic microorganisms to cause respiratory tract infections. Changes may also occur in common microorganisms such as penicillin-resistant pneumococci or multidrug-resistant Mycobacterium tuberculosis. Finally, usual pathogens may result in unusual manifestations.