Pneumonias in adults due to mycoplasma, chlamydiae, and viruses are a common clinical problem. These microorganisms cntribute to the etiologies in 6-35% of all cases of pneumonia and are the sole pathogens in 1-17% of hospitalized cases. Important trends and developments in the field include (1) the emergence of a Chlamydia psittaci strain (TWAR) that is passaged from human to human, causes a mycoplasma-like illness, and that is relatively resistant to erythromycin, (2) the recognition of respiratory syncytial virus as a pathogen in nursing home outbreaks and in immunosuppressed adults, (3) the continuing high lethality of fully developed influenza pneumonia, (4) the efficacy of acyclovir and adenine arabinoside in limiting the complications of varicella-zoster virus infections, and (5) the increasing frequency of pneumonia caused by cytomegalovirus and the severity of this disorder in highly immunosuppressed patients. Developments in the rapid diagnosis and therapy of respiratory syncytial virus infections with an aerosolized antiviral drug in children may pave the way for comparable advances in difficult pneumonias in adult patients.
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