• HIV infection

  • Radiation treatment

  • Immunosuppressive medications for transplantation, therapy of malignancy (chemotherapy), or treatment of autoimmune disease

  • Malnutrition

  • Pregnancy

  • Severe trauma and burns

  • Other concurrent infections

  • Malignancy

Immunosuppression can result in disease in an individual who otherwise would have been able to fend off illness. Infections caused by typically nonthreatening organisms that take advantage of a person's weakened state are called opportunistic infections.

Although opportunistic infections have received a great deal of attention over the past decade with the onset of the HIV disease pandemic, they are not new. During the pandemics of influenza in the early part of this century, it was well understood that both the very young (who have immature immune systems) and the elderly (who have waning immune defenses and, often, concurrent disease) were in the greatest danger of succumbing to this viral disease. New medical treatments and technologies—for example, therapy for collagen-vascular diseases like rheumatoid arthritis and vasculitis, cancer chemotherapy, and organ transplantation—have created additional openings for opportunistic pathogens.

There is good reason to believe that opportunistic infections will continue to threaten human health. The mean age of the U.S. population continues to rise. More and more people are surviving into their eighties and nineties, when previously non-life-threatening infections become common killers. Suboptimal prenatal care for women of lower socioeconomic status, which often results in premature and disease-prone infants, will likely continue to be the norm. The number of people with AIDS will continue to grow as those who became infected years ago develop full-blown disease. The HIV-infected population serves as a particularly important point of surveillance for emerging opportunistic infections because of its size and because the immunosuppression that characterizes the disease is comprehensive.

In many cases, knowledge of the type and extent of a person's immune dysfunction makes it possible to predict the kinds of infections that person is likely to acquire. When immune deficiency is acute and general in nature, however, any number of infections are apt to result, often simultaneously and often with astounding intensity. Such is the case for people with HIV disease. It is not surprising that opportunistic infections account for 90 percent of all HIV disease-related deaths (Double Helix, 1990).

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