Respiratory infections in the immunocompromised patient.

Damage to local and systemic defences of the lungs makes the immunocompromised host vulnerable to inhaled microorganisms. The type of underlying disease and its associated immunodeficiency allow a high degree of accurate pathogen prediction. Neutropenia is associated with Gram-negative bacilli pneumonia. Prolonged neutropenia increases the risk of aspergillosis and mucormycosis. Cellular immunodeficiency is associated with Pneumocystis carinii, Legionella spp. and intracellular parasites including Mycobacteria spp., Nocardia spp. Rhodococcus equi, cytomegalovirus, Strongyloïdes stercoralis, Histoplasma capsulatum and Coccidioides immitis. Humoral immunodeficiency predisposes to infection with Streptococcus pneumoniae and Haemophilus influenzae. Chest computerized tomography scan and bronchoalveolar lavage are essential procedures for diagnosis. Successful therapy depends on the type of pathogen, status of host defence sand early adequate choice of antibiotics. Enhancement of host defences with growth factors, cytokines and interferons can ameliorate the outcome.