Diagnosis of Infectious Diseases in the Lower Respiratory Tract: A Cytopathologist's Perspective.

CONTEXT.—: Respiratory cytology continues to play an important role in the diagnosis of lower respiratory tract infections. Prompt, accurate diagnosis of causative organisms is of paramount importance, particularly in immunosuppressed patients. In addition, a rapidly expanding arsenal of ancillary testing is now available, aiding tremendously in organism identification. OBJECTIVE.—: To provide an updated review on the cytomorphologic features of common organisms in lower respiratory tract infection. Relevant ancillary tests, differential diagnoses, and potential pitfalls of organism identification will also be discussed. DATA SOURCES.—: Data for this review were gathered from PubMed searches of infectious diseases of the lower respiratory tract, especially related to the diagnoses. CONCLUSIONS.—: The lower respiratory tract is subject to infection by a wide variety of infectious agents. Pathologists should be familiar with common organisms, including their general clinical characteristics, cytomorphologic features, differential diagnoses, and ancillary methods of detection. Above all, correlation with microbiologic and clinical information is necessary to make a confident diagnosis of infection.