Risk factors for positive admission surveillance cultures for methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci in a neurocritical care unit*
Authors: Minhas Paras , Perl Trish M. , Carroll Karen C. , Shepard John W. , Shangraw K. Alexander , Fellerman Donna , Ziai Wendy C. 
Published: June 2011

Objective:
Hospitals are under increasing pressure to perform active surveillance cultures for methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus. This study aimed to identify patients at low and high risk for positive admission surveillance cultures for methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus in a neurocritical care unit using readily ascertainable historical factors.

Design:
Before/after study with nested case/control study.

Setting:
Neurocritical care unit of an academic hospital.

Patients:
During the intervention period (July 2007 to June 2008), after implementation of an admission surveillance culture screening program for methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus, 2,059 patients were admitted to the neurocritical care unit for a total of 5,957 patient days.

Interventions:
Cases had positive methicillin-resistant Staphylococcus aureus or vancomycin-resistant Enterococcus admission surveillance cultures within 48 hrs of hospital admission. Controls had negative cultures.

Measurements and Main Results:
Admission surveillance cultures grew methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus in 35 of 823 (4.3%) and 19 of 766 (2.5%) patients, respectively. Factors significantly associated with both methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus colonization were intravenous antibiotics and hospitalization in the past year, immunocompromised health status, intravenous drug use, long-term hemodialysis, and known prior carrier status. Transfer from an outside hospital and residence in a long-term care facility in the past year were associated with vancomycin-resistant Enterococcus colonization. Classification and regression tree analysis was used to identify variables that best predicted positive methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus surveillance cultures. A classification and regression tree model with six of these variables yielded an overall cross-validated predictive accuracy of 87.12% to detect methicillin-resistant Staphylococcus aureus colonization. For vancomycin-resistant Enterococcus, a four-variable classification and regression tree model (intravenous antibiotics, hospitalization and long-term patient care in the past year, and not being “admitted same day of procedure”) optimized the predictive accuracy (94.91%). There were no cases of vancomycin-resistant Enterococcus colonization in patients admitted same day of procedure.

Conclusions:
Colonization with methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus in neurocritical care patients can be predicted with a high predictive accuracy using decision trees that include four to six readily attainable risk factors. In our setting, in the absence of these risk factors and in patients admitted from home for neurosurgical procedures, routine admission surveillance cultures to the intensive care unit may not be cost-effective.