Aging and nosocomial infections

The aging of the population represents another factor driving the nosocomial infection epidemic. While in 1900 only 1 percent of the world's population (15 million people) was greater than 65 years of age, by 1992 this proportion had grown to 6 percent (342 million people). By 2050, it's estimated that 2.5 billion world inhabitants will be older than 65 (Strausbaugh, 2001). Several factors may increase elderly patients' risks of acquiring HAIs. Their immune function and natural defenses may be decreased. Older patients have less robust T-lymphocyte proliferation, leading to decreased antibody production and cell-mediated immune function with increasing age. Conditions more prevalent in the elderly, such as diabetes, malignancy, vascular disease, and dementia, also may decrease barriers to infection. Functional incapacity due to aging may necessitate use of invasive devices, such as urinary catheters or feeding tubes, which further bypass the body's natural defenses. Incapacity and immobility may also lead to skin breakdown and the risk of infected pressure sores (Strausbaugh, 2001).

Old-age specific risk factors have translated into increased rates of HAIs for the elderly. NNIS data from 1986 to 1990 showed that persons greater than 65 years of age acquired 54 percent of all nosocomial infections (Emori et al., 1991). While decade-specific HAI rates were 10 per 1000 hospital days for patients up to the fifth decade of life, patients greater than 70 had more than 100 HAIs per 1000 hospital days (Gross et al., 1983). HAIs in the elderly also may affect outcomes more dramatically. For instance, comparing younger patients with S. aureus surgical site infection (SSI) with elderly S. aureus SSI patients, researchers found that elderly patients had a three-fold greater chance of death, longer hospital stays (13 vs 9 days), and higher hospital costs ($85,658 vs $45,767) (McGarry et al,, 2004).

Living arrangements of elderly patients also may place them at greater risk for HAIs. Ninety percent of long-term care facility (LTCF) residents are greater than 65 years old (Capitano and Nicolau, 2003). The LTCF setting itself may contribute to elderly patients' increased risk for HAIs. The closed institutional setting increases LTCF residents' exposure to bacteria via frequent contact with staff and other residents, and in facilities with antiquated air-ventilation systems, exposure to airborne respiratory pathogens may be exacerbated (Yoshikawa, 2000).

LTCF residents acquire 2-4 million HAIs annually (Garibaldi, 1999), representing a rate of 4-8 infections per 1000 patient days (Capitano and Nicolau, 2003). The transfer into LTCFs of patients colonized or infected by resistant organisms during stays in acute-care hospitals, and selection pressure created by frequent LTCF use of antibiotics, lead to high rates of antimicrobial resistance. One survey of residents from 25 LTCFs found that 38 percent were receiving antibiotics; bacterial isolates from those residents were resistant to the prescribed antibiotic in 65 percent of cases (Capitano and Nicolau, 2003). The combination of at-risk, elderly residents and frequent antibiotic use led a prominent antibiotic resistance researcher to label LTCFs as antibiotic-resistance "factories" (Levy and Marshall, 2004).

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