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Immunocompromised patients defined as those with
HIV disease
Absolute neutrophil counts < 1000/mcL (< 1.0 × 109/L)
Current or recent exposure to myelosuppressive or immunosuppressive medications, or those currently taking > 20 mg/day of prednisone or equivalent for > 4 weeks
May arise from infectious or noninfectious causes
Infectious: bacterial, mycobacterial, fungal, protozoal, helminthic, or viral pathogens
Noninfectious processes: pulmonary edema, alveolar hemorrhage, medication reactions, pulmonary thromboembolic disease, malignancy, and radiation pneumonitis may mimic infection
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Chest radiography is rarely helpful in narrowing the differential diagnosis
Examination of expectorated sputum for bacteria, fungi, mycobacteria, Legionella, and P jirovecii is important and may preclude the need for expensive, invasive diagnostic procedures
Bronchoalveolar lavage using the flexible bronchoscopy
Safe and effective method for obtaining representative pulmonary secretions for microbiologic studies
Involves less risk of bleeding and other complications than transbronchial biopsy
Especially suitable for the diagnosis of P jirovecii pneumonia in patients with AIDS when induced sputum analysis is negative
Surgical lung biopsy, now often performed by video-assisted thoracoscopy, provides the definitive option for diagnosis
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Routine evaluation frequently fails to identify a causative organism
Empiric antimicrobial therapy may be started before proceeding to invasive procedures such as bronchoscopy, transthoracic needle aspiration, or open lung biopsy
The approach to management must be based on the severity of the pulmonary infection, the underlying disease, the risks of empiric therapy, and local expertise and experience with diagnostic procedures