Severe Q fever community-acquired pneumonia (CAP) mimicking Legionnaires' disease: Clinical significance of cold agglutinins, anti-smooth muscle antibodies and thrombocytosis.

Atypical community-acquired pneumonia (CAP) may be caused by zoonotic or nonpulmonary pathogens. However, atypical pathogens are systemic infectious disease accompanied by pneumonia in contrast with typical bacterial pathogens with infection limited to the lungs and absent extrapulmonary findings. Clinically and radiologically, the atypical CAP pathogens that most closely resemble each other are psittacosis, Q fever, and Legionnaires' disease.

Fever of unknown origin (FUO) due to cyclic neutropenia with relative bradycardia.

Fever of unknown origin (FUO) is the diagnosis associated with a variety of infectious, neoplastic, or rheumatic/inflammatory disorders. FUOs are associated with fevers of > or = 101 degrees F for > or = 3 weeks that remain undiagnosed after intensive in-hospital or ambulatory investigation. Many FUOs caused by rheumatic/inflammatory disorders are particularly difficult to diagnose because of the lack of specific diagnostic tests for many of these disorders.

Severe cytomegalovirus (CMV) community-acquired pneumonia (CAP) precipitating a systemic lupus erythematosus (SLE) flare.

Cytomegalovirus (CMV) is a virus that infects both normal and compromised hosts. In normal hosts, CMV presents most often as an "infectious mononucleosis-like" illness, but less commonly may present as community-acquired pneumonia (CAP), colitis, hepatitis, or fever of unknown origin. In compromised hosts, CMV often presents as CAP, encephalitis, retinitis, adrenalitis, hepatitis, or colitis.

Q fever community-acquired pneumonia in a patient with Crohn's disease on immunosuppressive therapy.

Community-acquired pneumonia (CAP) may be caused by typical or atypical pathogens. The three most common zoonotic atypical pathogens are Chlamydophila psittaci (psittacosis), Francisella tularensis (tularemia), and Coxiella burnetii (Q fever). Atypical CAPs are suggested by a distinctive pattern of extrapulmonary organ involvement.