The explanation for these surprising findings is unknown, but the possibilities may include a tendency by physicians to avoid surgery in frail elderly patients and, conversely, a "hardy survivor" effect, in which a protective genetic makeup may enable elderly patients to withstand the rigors of surgery and its complications.
Keith S. Kaye, MD, MPH, and colleagues at Duke University Medical Center and Durham Veterans Affairs Medical Center studied 144,485 patients over age 16 years with no pre-existing surgical-site infections who were admitted for surgery to 11 hospitals in the southeastern United States between Feb. 1, 1991 and July 31, 2002; the most common surgical procedures were orthopedic (42 percent), gastrointestinal (13 percent), obstetric/gynecologic (11 percent), or cardiothoracic (10 percent). Of the 144,485 patients studied, surgical-site infections developed in 1,684 (1.2 percent), with gastrointestinal procedures (3.1 percent), cardiothoracic procedures (2.3 percent), and vascular procedures (1.7 percent) having the highest rates
Between ages 17 and 65 years, the infection rate increased for each decade of increasing age, peaked at ages 65 to 74, and then decreased for each subsequent decade. This "inverted V" pattern was also seen when the investigators randomly divided the patients into two groups so that age and infection risk could be analyzed in one subgroup and the findings confirmed in the other.
The Duke investigators were surprised by their results, noting that previous studies of the relationship between age and surgical-site infections had provided conflicting results and had had numerous limitations, including small sample size and data restricted to a single institution or a single surgical category.
In an editorial accompanying the study, Thomas R. Talbot and William Schaffner of Vanderbilt University noted that the toll of surgical-site infections is immense: approximately 500,000 of the infections occur each year in the United States, "leading to an estimated 3.7 million excess hospital days and over $1.6 billion in excess costs." They commented that the study by Kaye and colleagues was "impressive," even though it had its own limitations, including a heavy reliance on data from community hospitals, whose patients may be less severely ill than those in a university hospital and thus may have a lower risk of surgical-site infections.
Nevertheless, Talbot and Schaffner concluded that the sheer volume of patients and procedures studied afforded substantial power to the findings. Future investigations of the role of age in surgical-site infections, they noted, should address questions raised by the Duke study--namely, are older patients more likely to be medically, rather than surgically, managed compared to younger patients? Among surgical patients, are older patients more likely to undergo conservative procedures, and younger patients aggressive procedures? Do trends in patient referral and selection differ according to surgical procedure? And if increasing age is truly associated with decreased risk for surgical-site infections, is there a biologically plausible explanation for the effect?
Founded in 1904, The Journal of Infectious Diseases is the premier publication in the Western Hemisphere for original research on the pathogenesis, diagnosis, and treatment of infectious diseases; on the microbes that cause them; and on disorders of host immune mechanisms. Articles in JID include research results from microbiology, immunology, epidemiology, and related disciplines. JID is published under the auspices of the Infectious Diseases Society of America (IDSA). Based in Alexandria, Va., IDSA is a professional society representing about 8,000 physicians and scientists who specialize in infectious diseases. For more information, visit www.idsociety.org.
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