What should you do if an employee tests positive for the virus?
 the infected employee should not be permitted to return to the workplace until they are clear of COVID-19;
 immediately contact the local health unit for guidance and to initiate contact tracing;
 in most cases, you do not need to shut down your entire workplace. Rather, you can close off any areas that were used for prolonged periods of time by the sick person, and then (ideally after waiting 24 hours) thoroughly clean and disinfect those areas.
 take additional steps to determine which other employees had worked closely with the infected person and inform them of their exposure risk. Employers should, as much as possible, maintain confidentiality about the identity of the specific person who was infected. For employees who were exposed to the infected person for prolonged periods of time, ask them to self-isolate and stay home/work remotely for 14 days to reduce the risk of the infection spreading in the workplace, but seek the guidance of the local health unit before doing so.
The above steps should be taken promptly once an employer is notified of a COVID-19 infection in their workplace.
The physical layout of each workplace is different. Each workplace may also have a different level of interaction between employees in the workplace. The infected employee may not have attended the workplace often before testing positive. All of these factors will be relevant to determining which employees worked closely with, or had prolonged exposure to, an infected employee.
To address some of these issues proactively, larger workplaces can separate employees into cohorts or working groups to reduce the chance of the virus spreading and to make exposures easier to manage.