Infections in People With Impaired Defenses
Many diseases, drugs, and other treatments can cause a breakdown in the body's natural defenses. Such a breakdown can lead to infections, which can even be caused by microorganisms that normally live harmlessly on or in the body.
People with extensive burns have an increased risk of infection because damaged skin cannot prevent invasion by harmful microorganisms. People undergoing medical procedures that introduce foreign material into the body have an increased risk of infection. Such procedures include the insertion of a catheter into the urinary tract or a blood vessel, or the insertion of a tube into the windpipe. Many drugs can suppress the immune system, including anticancer drugs (chemotherapy), drugs used to prevent organ rejection after a transplant (such as azathioprine, methotrexate, and cyclosporine), and corticosteroids (such as prednisone). Radiation treatments may suppress the immune system, particularly when the bone marrow receives radiation.
The ability to fight certain infections decreases dramatically in people with AIDS, especially late in the disease (see Section 17, Chapter 199). People with AIDS are at particular risk for opportunistic infections (infections by microorganisms that generally do not cause infection in people with a healthy immune system). They also become more severely ill from many common infections.
Infections are more likely and usually more severe in older people than in younger people, probably because aging reduces the immune system's effectiveness (see Section 16, Chapter 183). Many long-term (chronic) disorders that are common in older people--such as chronic obstructive pulmonary disease, cancer, and diabetes mellitus--also increase the risk of infection. In addition, older people are more likely to be in a hospital or a nursing home, where the risk of acquiring a serious infection is greater. In hospitals, the widespread use of antibiotics allows antibiotic-resistant organisms to thrive, and infections with these microorganisms are often more difficult to treat than infections acquired at home.
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