Two family members of the Morningside Medi-Clinic nurse who died of a viral disease have been put into isolation as a precautionary measure, the hospital said on Tuesday.

“We admitted them for observation under strict isolation regulations but none of them have shown any symptoms,” said regional marketing manager Melinda Pelser.

She said it had been confirmed that the three people who died of a “mysterious disease” at the clinic had suffered from a viral haemorrhagic fever but the cause of the disease was not yet known.

The Centre for Disease Control and Prevention in Atlanta was working with health officials in South Africa to investigate the cause, she said.

Pelser also said it had been confirmed that the cleaner who worked for a contract company at the hospital did not die from the viral fever.

“She died of a neurological illness. It has been established that she was not near the patient,” said Pelser.

The first casualty who succumbed to the viral disease was a 36-year-old woman who was airlifted from Zambia to the Morningside Medi-Clinic in Sandton on September 12.

She was treated for tick-bite fever and other potential infections but died two days later.

A Zambian paramedic who had accompanied her into the country died last week and a nurse at the Morningside Medi-Clinic died on Sunday. The cleaner also died on Sunday.

Pelser said the incubation period for the disease was between 72 hours and 21 days.

“We know that it is not airborne and is contracted through the bodily fluids of the infected person,” she said.

Symptoms include high fever, muscle aches and pains, diarrhoea and a rash.