The person should be isolated immediately in a temporary workplace isolation room and
the Employer has to arrange for the worker to be transported for a medical examination or testing in a manner that does not place other workers or members of the public at risk. So this will include not sending them home in public transport. However, if the employee has screened positive before entering the premises, the employer may deny them entry onto the work premises.
There are guidelines on the NIOH website on various scenarios.
The directive from the Department of Employment and Labour also gives guidance on what all workplaces should have in place in this time of COVID-19