In May of 2020, the Substance Abuse and Mental Health Service Administration (SAMSA) issued guidelines for state psychiatric hospitals, recommending that these facilities adopt universal testing for COVID-19 and "three-space" triage protocols for dedicated COVID-19 positive, negative, and quarantine spaces to mitigate the risk of nosocomial infection. The Westchester Behavioral Health Center of New York Presbyterian Hospital (WBHC-NYP) adopted a comprehensive infection control protocol consistent with these recommendations in April, 2020. We reviewed the records of 1,139 patients treated on the inpatient service at WBHC-NYP between March 14th and June 10th, 2020, dates corresponding to the first COVID-19 surge in the New York City metropolitan region. The incidence of detected nosocomial or possible nosocomial infections before and during the implementation of the protocol was 0.096 (16/167), or 0.96 infections per 10 at-risk patients. The incidence of nosocomial or possible nosocomial infections after complete implementation was 0.0110 (2/182), or 1.1 infections per 100 at-risk patients. The difference in incidence between the two time points was statistically significant (p<.0003) and represents a 9-fold decrease.  Our findings support the institutional use of a combined testing and space allocation protocol to mitigate risk of outbreaks in confined settings.