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Chapter: Medical Microbiology: An Introduction to Infectious Diseases: Infections in the Immunocompromised Patient

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Clinical Situations Associated With Infection

The increasing worldwide prevalence and profound immunodeficiency of AIDS remains a major concern.

CLINICAL SITUATIONS ASSOCIATED WITH INFECTION

Acquired Immunodeficiency Syndrome

The increasing worldwide prevalence and profound immunodeficiency of AIDS remains a major concern. Most patients die of human immunodeficiency virus infection per se or as a direct result of one of the opportunistic infections mentioned earlier.

Malignancies

Although some malignancies compromise the immune system directly, the chemothera-peutic agents used to treat them are the primary cause of immunosuppression. In particu-lar, the periods of granulocytopenia between the administration of high-dose chemother-apy and recovery of granulocyte-producing function are associated with infection. The organisms most common during this vulnerable period are generally the same as among the general population; for example, Staphylococcus aureus andEscherichia coli, but other pathogens such as P. aeruginosa and Candida albicans are more prominent than in the immunocompetent individual. As discussed earlier, chemotherapy may also compro-mise cell-mediated immunity, in which case infections due to intracellular bacteria and viruses are common. Finally, chemotherapy may damage mucosa (oral, intestinal, vagi-nal, rectal), allowing ingress of bacteria, fungi or viruses.

Transplantation

Solid organ and bone marrow transplantations are among the most important advances in modern medicine. Their success depends to a great degree on the ability to control and manage the undesired aspects of the immunosuppressive regimens, primarily the suscepti-bility to infection as long as immunosuppression is used. The pattern of microorganisms varies with the type of transplant, as does the immunosuppressive therapy, but viruses are extremely important. Viruses of the herpesvirus family, such as herpes simplex, varicella – zoster, and cytomegalovirus are the most common, but respiratory syncytial virus and other respiratory viruses are also important. Bacteria associated with deficiencies in granulocytes and cell-mediated immunity are also involved; Legionella and Nocardia infections have been particularly prominent in kidney and heart transplant recipients and fungal infections are common. Recombinant granulocyte-macrophage colony-stimulating factor can acceler-ate the recovery of bone marrow myeloid elements in bone marrow transplant and some cancer chemotherapy patients, sometimes reducing the period of vulnerability.

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