Health care-associated infection: assessing the value and validity of our measures

National recommendations for health care-associated infection and transmission metrics have arisen to address the diversity of health care measures in use today. Many of these recommendations include valuable proxy measures, which are simplifications of formal epidemiologic definitions. These proxies provide feasible real-time metrics for ongoing infection control programs. However, the maximum value of these measures is derived from understanding their benefits and limitations when applied to specific populations. Proxy measures should not be dismissed solely because they are imprecise; rather, the source and magnitude of imprecision should be evaluated on the basis of the likelihood that they adversely affect interpretive judgment and subsequent action. This review provides examples of common proxies used in infection control and prevention programs to discuss differences between proxies and exact epidemiologic measures, the value of those differences, and how to assess when exact measures should be used to supplement or replace proxy measures.