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.
OBJECTIVE
To develop and validate an algorithm to identify and classify noninvasive infections due to Staphylococcus aureus by using positive clinical culture results and administrative data.


METHODS
Retrospective cohort study.


METHODS
Veterans Affairs Maryland Health Care System.


METHODS
Data were collected retrospectively on all S. aureus clinical culture results from samples obtained from nonsterile body sites during October 1998 through September 2008 and associated administrative claims records. An algorithm was developed to identify noninvasive infections on the basis of a unique S. aureus-positive culture result from a nonsterile site sample with a matching International Classification of Diseases, Ninth Revision (ICD-9-CM), code for infection at time of sampling. Medical records of a subset of cases were reviewed to find the proportion of true noninvasive infections (cases that met the Centers for Disease Control and Prevention National Healthcare Safety Network [NHSN] definition of infection). Positive predictive value (PPV) and negative predictive value (NPV) were calculated for all infections and according to body site of infection.


RESULTS
We identified 4,621 unique S. aureus-positive culture results, of which 2,816 (60.9%) results met our algorithm definition of noninvasive S. aureus infection and 1,805 (39.1%) results lacked a matching ICD-9-CM code. Among 96 cases that met our algorithm criteria for noninvasive S. aureus infection, 76 also met the NHSN criteria (PPV, 79.2% [95% confidence interval, 70.0%-86.1%]). Among 98 cases that failed to meet the algorithm criteria, 80 did not meet the NHSN criteria (NPV, 81.6% [95% confidence interval, 72.8%-88.0%]). The PPV of all culture results was 55.4%. The algorithm was most predictive for skin and soft-tissue infections and bone and joint infections.


CONCLUSIONS
When culture-based surveillance methods are used, the addition of administrative ICD-9-CM codes for infection can increase the PPV of true noninvasive S. aureus infection over the use of positive culture results alone.
Tracy
LaRee A
LA
Department of Epidemiology and Preventive Medicine, University of Maryland, Baltimore, Maryland, USA. ltracy@epi.umaryland.edu
Furuno
Jon P
JP
Harris
Anthony D
AD
Singer
Mary
M
Langenberg
Patricia
P
Roghmann
Mary-Claire
MC
D000465:Algorithms; D001431:Bacteriological Techniques; D015331:Cohort Studies; D003470:Culture Media; D006801:Humans; D038801:International Classification of Diseases / Q000592:standards*; D008396:Maryland; D011237:Predictive Value of Tests; D013203:Staphylococcal Infections / Q000175:diagnosis* / Q000382:microbiology; D013211:Staphylococcus aureus / Q000145:classification / Q000302:isolation & purification*; D014481:United States; D014493:United States Department of Veterans Affairs
D003470:Culture Media