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Nosocomial or hospital-associated infections are adverse patient events that affect approximately 1.7 million persons and contribute to approximately 99,000 deaths annually in the United States.1 The annual economic burden of these infections in the United States is estimated at $6.7 billion per year, in 2002 prices.2 Hospital-associated infections are one of the most common complications affecting hospitalized patients. One type of hospital-associated infection, surgical-wound infection, constitutes the second largest category of all hospital-associated adverse events, after drug-related events.3

During the past decade, health care in the United States has been increasingly delivered in a variety of settings, such as outpatient, long-term care, and home health settings. Invasive procedures are now frequently performed on an outpatient basis. Although the U.S. population has grown about 38% since the 1970s, the number of hospital admissions remains at 1975 levels (36.3 million in 2002 compared to 36.2 million in 1975); in contrast, the number of outpatient visits increased 2.5 times (to 640.5 million from 254.8 million).4 Further, the number of certified ambulatory surgical centers increased tenfold, from 336 in 1985 to 3371 in 2002. These changes result in an inpatient population that is more likely to have severe illnesses5 and be older.4

Because of the evolution in health care, the term “health care-associated infection” (HAI) has become more appropriate than “nosocomial infection,” since the latter is restricted to the hospital setting. Within hospitals, for many years, the highest rates of infections were observed in intensive care units (ICUs).6,7,8 However, recent studies have shown that procedures that pose a risk of infections (e.g., use of central venous catheters (CVC)) are also frequent outside ICUs. One study involving six medical centers revealed that 29% of 2459 patients had CVCs including 7–39% (mean 24%) of non-ICU patients.9

The epidemiology of HAI is best described in hospital ICUs and will be the focus of this chapter.

In general, HAIs are infections that are not present or incubating at the time of admission to the hospital or health-care facility.10 Infections are the most frequent adverse event in health care11 and occur at a rate of approximately 5–10 per hundred admissions.1,12 Many HAI are associated with an increased length of stay, prolonged therapy,13,14 and increased costs.15 Mortality is high: 26.6% of all deaths in a multihospital study were associated with an HAI.16 Among persons with a health care-associated bloodstream infection, the attributable mortality can be higher (35%).17,18,19

Data from the Study on the Efficacy of Nosocomial Infection Control (SENIC) suggested that about a third of hospital-associated infections could have been prevented in the mid-1970s if effective infection control programs were in place;20 however, a review of more recent studies suggests that preventability ...

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