Pulmonary infiltrates

The lungs are a frequent site of bacterial, fungal, and viral infection.9 The radiographic pattern on Chest X-ray

(CXR) or CT is helpful. Lobar infiltrates are uncommon, but may reflect postobstructive pneumonia. Bacterial infection more commonly appears as patchy, sometimes multilobar infiltrates. Diffuse infiltrates suggest viral or overwhelming bacterial or fungal pneumonia, or nonin-fectious etiologies such as pulmonary hemorrhage. Nodular infiltrates are more likely to be fungal, nocar-dial, or mycobacterial. The presence of cavitary lesions suggests fungi, mycobacteria, bacterial lung abscess, septic pulmonary emboli, or tumor. The "halo sign" is often indicative of aspergillosis.10 Evidence of old granuloma-tous disease, such as calcified hilar lymph nodes, suggests dormant fungal or mycobacterial infection that could reactivate in the neutropenic patient.

Patients with pulmonary infiltrates may progress rapidly to respiratory failure and mechanical ventilation. This should prompt broadening of the antibiotic regimen, including systemic antifungal therapy. Patients whose white blood cell counts begin to recover may actually experience a respiratory exacerbation.

Bronchoscopy with bronchoalveolar lavage (BAL) is far more likely than sputum to yield a diagnosis, but BAL cultures may show no growth even in active infection, particularly with prior antibiotic therapy. The BAL is more sensitive for Pneumocystis than for fungi, and mycobacteria often require protracted time to grow. CMV in BAL cultures is not necessarily indicative of CMV pneumonitis. Lung biopsy can add considerably to the diagnostic yield of bronchoscopy, but severe throm-bocytopenia makes transbronchial biopsy problematic. Open lung biopsy may be warranted in such situations.

Aspiration pneumonia may occur, particularly in elderly patients or those with mental status changes or severe nausea and vomiting. In this situation, bronchoscopy is often nondiagnostic or may grow mixed flora.

Infection control issues are important in patients with pulmonary infiltrates, as devastating outbreaks of respiratory viral infection have occurred (influenza, parainfluenza, RSV, and adenovirus).11 During influenza season, or any time a community-acquired respiratory virus is suspected, any patient with an unexplained infiltrate should be placed in respiratory isolation initially.

Other causes of pulmonary infiltrates can mimic infection, and should be considered. These include pulmonary hemorrhage, septic pulmonary emboli, congestive heart failure, chemotherapy and radiation toxicity, and adult respiratory distress syndrome from nonpulmonary sepsis.

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