Pulmonary infections in the immunocompromised host.

The expression "immunocompromised host" refers to an individual who has one or more defects in the body's natural defense, which leads to severe, often life-threatening, infections. Alcoholism, diabetes mellitus, advanced age, the use of antacids, and viral infections have immune-modulating effects. The human immunodeficiency virus, cytomegalovirus, Epstein-Barr virus, and Non A, Non B hepatitis virus also contribute to immunosuppression. The lung has a special vulnerability to infection, and pneumonia accounts for more than 40% of deaths in the immunosuppressed population. Diagnostic methods include detection of microbial antigens by monoclonal antibodies, DNA sequences by the polymerase chain-reactions or DNA probes, and unique metabolites of pathogens by gas chromatography. Transtracheal aspiration was used to obtain uncontaminated respiratory secretions, but fiberoptic bronchoscopy with shielded brush and bronchoalveolar lavage (BAL) is a better means of diagnosis because of a 90% sensitivity in diagnosing pneumocystis infection. Percutaneous aspiration and open lung biopsy are reserved for more complicated cases. Empiric treatment is justified in far advanced AIDS or relapsed myelogenous leukemia with limited life expectancy, or when there is uncontrollable bleeding diathesis or impaired pulmonary function as invasion diagnostic procedures will not be tolerated. The most important antiinfective measure is careful hand washing, while prophylactic antibiotics, selective decontamination, and antifungal, antiviral, and antiparasitic agents can be used. Active and passive immunization against specific pathogens, immunological reconstitution with granulocyte-macrophage colony-stimulating factor (GM-CSF) and reducing the dosage of immunosuppression are the other strategies for prevention. In the last several decades there has been substantial progress in the management of chronic diseases which used to be fatal.