The problem is likely to grow even more serious with time, given the Agency for Health Care Policy and Research's estimates that 43 percent of all those who turned 65 years old in 1990 will enter a nursing home at some point in their lives (Agency for Health Care Policy and Research, 1990).

In sum, hospitals and long-term care facilities can no longer be viewed as isolated epidemiological units but must be seen as part of a network of patient care facilities. This network makes it possible for nosocomial and community-acquired infections to be rapidly and widely spread.

PREVENTION OF NOSOCOMIAL INFECTIONS

Studies show, surprisingly, that even under the most sanitary of conditions, only about a third to a half of all hospital-acquired infections are preventable (Schaechter et al., 1989; Martone, 1990). Several factors "stack the deck" against infection control efforts. Little can be done to eliminate most of these risk factors, which include age (newborns and the elderly have limited immunity), severity of illness (related to length of stay, also a risk factor), and underlying diseases (latent infections or immune deficiencies) (Freeman and McGowan, 1978). Increased attempts at prevention for high-risk patients may be the only weapon against infection in these circumstances.

Two recent approaches to controlling hospital-acquired infections have been remarkably successful: CDC's 1987 "Universal Blood and Body Fluid Precautions" and hepatitis B vaccination. Under the universal precautions, blood and certain body fluids of all patients are considered potential sources of HIV, hepatitis B virus (HBV), and other blood-borne pathogens. The guidelines are a revision of a 1983 document that recommended special precautions (use of gloves and other protective barriers, and careful handling and disposal of needles and other sharp instruments) for blood and body fluids of patients known or suspected to be infected with blood-borne pathogens. The hepatitis B vaccine was licensed in 1982.

Statistics demonstrate the impact of these two infection control measures. A recent study by the Hepatitis Branch at CDC documented a 75 percent decrease in cases of hepatitis B among health care workers in four sentinel counties between 1982 and 1988 (Alter et al., 1990). The study's authors surmised that the decrease in cases was "probably a direct result of immunization with hepatitis B vaccine and of wider implementation of universal blood precautions" (Alter et al., 1990).

Although the hepatitis B story clearly can be counted as a victory for hospital infection control, new microbial threats are likely to surface in the future. Health care institutions are prime breeding grounds for new and more virulent strains of organisms and may well represent one of the most



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