Striving for benchmark infection rates: progress in control for patient mix

The outcome of clinical events has become the major focus for quality assurance programs in the United States. Assessment of outcome depends on the availability of accurate benchmark rates appropriate to the clinical situation. Although mortality, length of stay, cost, and other resource utilization measures are important outcome events for review, nosocomial infection is one of the best-studied outcome events for which benchmark rates and distributions of rates are available. To monitor nosocomial infection acquisition, the Joint Commission on Accreditation of Healthcare Organizations (JCAHO) has proposed indicators for wound infections after clean and clean-contaminated surgical procedures, for pneumonia in intensive care units (ICUs), and for intravascular device infections in ICUs. From the National Nosocomial Infections Surveillance (NNIS) system, we know that the mean rate of surgical wound infections (SWIs) for clean-contaminated wounds is 2.7%. However, the range is too broad and depends on the types of surgical procedures and the patient risk factors in each category. As an example, the SWI rate for appendectomies is 2.2% while for colon surgery it is 7.1%. In addition, the patients should be stratified by underlying risk factors. For example, the NNIS risk index is composed of wound class, duration of surgery, and American Society of Anesthesiology score. Other commonly used severity of illness scores could be used, such as a comorbidity score or APACHE II. Other proposed JCAHO indicators are reviewed. Controlling for case mix and for severity of illness will be necessary for the development of benchmark infection rate distributions if clinical indicators are to be used as reliable quality assurance tools in the 1990s.