As of Apr 1, 2023 Public Health Ontario will implement a new modified two-tier testing (MTTT) for detection of antibodies against B. burgdorferi (Lyme Disease). The MTTT algorithm has been endorsed by the Centers for Disease Control and Prevention (CDC) as well as the Canadian Public Health Laboratory Network (CPHLN) as an acceptable alternative method to the standard two-tier testing (STTT). Sensitivity of MTTT is higher (15-25%) than STTT in detecting antibodies during early-localized Lyme disease. This session will give an overview of the new testing method and how these changes will impact public health operations (with respect to testing and reporting) and public health unit staff. An update on the current epidemiology of Lyme disease in Ontario will also be provided.