In fighting infectious disease outbreaks, a basic epidemiological principle is to detect cases quickly and to isolate each case, to interrupt transmission. This principle has been the cornerstone of the Carso Group (CG) COVID Protocol, a systematic blueprint for the reopening of operations of workplaces in the context of ongoing disease transmission in Mexico. The CG comprises over 50 companies with approximately 180,000 employees engaged in economic activities including telecommunications, retail, construction, banking, mining, and manufacturing, among others. To cope with the COVID-19 pandemic within the CG, the Carlos Slim Foundation designed, developed and implemented MONITOR, a digital health ecosystem comprising a mobile phone application, web portal, and analytics platform, to assess the infection risk of each employee, follow-up their health status, and detect early symptoms of COVID-19. MONITOR provides daily notifications for any suspected cases and activates a COVID-19 testing request and follow-up of results. This intervention helps rapidly identify and isolate suspected cases, as well as follow-up of work and family contacts, to prevent further outbreaks. Use of MONITOR has thus enabled containment of COVID-19 in workplaces and safe return to work. MONITOR is an example of the implementation of public health practices in workplaces and can serve as the basis for larger deployment in population-wide settings.