Legionnaire’s Disease and Severe Pneumonia Mimics in the Critical Care Unit

This chapter presents the clinical approach to the differential diagnosis (DDx) of severe community-acquired pneumonia (CAP) in the CCU, and some other causes of severe CAP that may clinically mimic Legionnaires disease. With severe CAP (SCAP), various etiologies may have radiographic and/or have overlapping clinical features or non-specific laboratory test abnormalities present with Leionnaires disease. In the DDx of severe CAP in the CCU, the CAPs most likely to resemble Legionnaires disease include influenza, influenza-like illnesses due to RSV, hMPV, HPIV-3, adenovirus, and M. pneumoniae, as well as S. pneumoniae. The severity of CAP depends on microbiologic and host factors and cardiopulmonary function.