Predictive ability of positive clinical culture results and International Classification of Diseases, Ninth Revision, to identify and classify noninvasive Staphylococcus aureus infections: a validation study.

During the past decade, there has been a dramatic increase in the incidence of infections due to community-associated methicillin-resistant Staphylococcus aureus (MRSA), many of which are skin and soft-tissue infections.1–3 Although the incidence of S. aureus infection in specific populations, and according to certain infection types, has been reported, the overall burden of S. aureus infection remains unclear. To improve the public health response to the nationwide epidemic of community-associated MRSA infections, a better estimate of the overall burden and distribution of all S. aureus infections is necessary. This requires a validated approach to identifying and classifying S. aureus infections according to type and severity, which is relatively straightforward for invasive S. aureus infections, because the presence of S. aureus in a specimen obtained from a normally sterile body site is highly predictive of infection. However, invasive S. aureus infections comprise only a small proportion of S. aureus infections. The greater challenge is to identify and classify noninvasive S. aureus infections, largely because in a clinical culture, S. aureus that is isolated from a sample obtained from a nonsterile body site can represent either infection or colonization. Although data on culture results are often available from large clinical databases, many of these results represent colonization rather than infection, because S. aureus is an opportunistic pathogen. Thus, a more predictive approach to identifying noninvasive S. aureus infections is needed, particularly because a substantial proportion of infections due to community-associated MRSA—specifically, skin and soft-tissue infections—are noninvasive.1,4 In addition, there is a need for an automated approach to identifying S. aureus infections for use in large epidemiological research studies for which medical record review is impractical or when medical records are unavailable. To address these needs, we performed a retrospective study in a large population of patients who receive healthcare services through the Veterans Affairs Maryland Health Care System (VAMHCS). Our research objective was to develop and estimate the accuracy of a new algorithm to identify and classify noninvasive S. aureus infections.