Background: Although active surveillance for multidrug-resistant organism (MDRO) colonization permits timely intervention, obtaining cultures can be time-consuming, costly, and uncomfortable for patients. We evaluated clinical differences between patients with and without attainable perianal cultures, and we sought to determine whether environmental surveillance could replace perianal screening. Methods: We collected active surveillance cultures from patient hands, nares, groin, and perianal area upon enrollment, at day 14, and monthly thereafter in 6 Michigan nursing homes. Methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), and resistant gram-negative bacilli (RGNB) were identified using standard methods. Patient characteristics were collected by trained research professionals. This substudy focused on visits during which all body sites were sampled. To determine the contribution of perianal screening to MDRO detection, site of colonization was categorized into 2 groups: perianal and non-perianal. We evaluated the utility of multisite surveillance (eg, type 1 and type 2 error) using nonperianal sites and environment surveillance. To evaluate characteristics associated with the acquisition of perianal cultures (eg, selection bias), we compared clinical characteristics, overall patient colonization, and room environment contamination of patients in whom all body sites were sampled during a study visit (533 patients; 1,026 visits) to patients with all body sites except the perianal culture sampled during a study visit (108 patients; 168 visits). Results: Of 651 patients, 533 met the inclusion criteria; average age was 74.5 years, 42.6% were male, and 60.8% were white. Of 1,026 eligible visits, 620 visits detected MDRO colonized patients; 155 MRSA, 363 VRE, and 386 RGNB (Table 1). If perianal cultures were not collected, nonperianal surveillance misses 7.7%, 41.3%, and 45.1% of MRSA, VRE, and RGNB colonized visits, respectively. The addition of environmental surveillance to non-perianal screening detected 95.5%, 82.9%, and 67.9% of MRSA, VRE, and RGNB colonized visits, respectively. The specificity of environmental screening was 85.3%, 72.7%, and 73.4% for MRSA, VRE, and RGNB, respectively. Patients without attainable perianal cultures had significantly more comorbidities, worse functional status, shorter length of stay, and higher baseline presence of wounds than patients with attainable perianal cultures; introducing potential selection bias to surveillance efforts (Table 2). No significant differences in overall patient colonization and room contamination were noted between patients with and without attainable perianal cultures. Conclusion: Perianal screening is important for the detection of VRE and RGNB colonization. Infection prevention must be cognizant of the tradeoff between reducing type 2 error and the selection bias that occurs with required attainment of perianal cultures. In the absence of perianal cultures, environmental surveillance improves MDRO detection while introducing type 1 error.