Government is worried about health workers who contract Covid-19 while performing their duties.
Health Minister Zweli Mkhize said this came after 48 of the 66 employees at the St Augustine's private hospital in Durban tested positive for the novel coronavirus this week.
Four people have died.
"This is a large number of staff to be infected in a particular institution. We have asked the provincial department of health to institute an investigation into why and how we ended with so many people infected in a particular institution.
"It is more serious to us because the first people we need to ensure are safe and protected, are the health workers. They deal on a daily basis with the infection," he said.
Mkhize said the hospital remained closed, except for a ward where Covid-19 positive patients were being treated.
"The closure means that there are no new outpatients and all sections are not operating. A number of wards are closed and fumigation processes have started as it was ordered by the department.
"From 80 patients the number has reduced to 58. Those patients can't be moved to other hospitals because the number was high and the hospital must begin to contain patients."
Mkhize emphasised the need to train healthcare workers about infection prevention.
"They must identify areas where there might be risks in private hospitals and do samples on staff so that we don't get a surprise of suddenly finding that there is an explosion of so many health workers who are positive in the area," Mkhize said.
"We need to keep a count of how many health workers are testing positive in any other parts of the country."
For more on the novel coronavirus and other stories listen to our podcast here on SoundCloud