Under the Prevention and Control of Disease Regulation if a health officer has reason to believe that a person has been, or is likely to have been, exposed to the risk of contracting an infectious disease (of which 2019-nCoV is one), then the health officer may place that person under quarantine or medical surveillance. 

If an employee is required or ordered by a health officer to be put under medical surveillance or quarantine, he/she will be issued with a medical certificate with the statement of "under medical surveillance". The employer will need to grant the employee sick leave in accordance with the Employment Ordinance and/or the relevant contract of employment.

For more information on an employer's obligation, see Novel Coronavirus and Employer Obligations.