Employees who are physically well but have self-tested positive for COVID-19 may work from home. If they can't work from home, you are strongly encouraged to grant them paid sick leave without requiring a medical certificate (MC).
Depending on your business needs, you should discuss with your employees and union (if relevant) and come to a mutual agreement on the sick leave period for COVID-19 positive but asymptomatic employees.
If there are disputes over the period of absence, you may require your employees to produce an MC so that they can be granted paid sick leave according to the Employment Act.