Two members of the family of a Morningside hospital nurse who died after coming into contact with the victim of a mystery disease last week were taken to hospital last night.
The hospital said the two were taken there for observation and tests after having been in contact with the nurse.
But, authorities said the infectious flu-like disease that has claimed the lives of four people in Johannesburg is not airborne.
The national Health Department has also said that the public should not panic.
The department's spokesman Fidel Hadebe said: "There is no need to panic at this stage because the only way one can be infected with this unknown deadly disease is through body fluids."
The fourth person to fall victim to the mystery disease died at Leratong Hospital on the West Rand yesterday.
She was a cleaner at Morningside Medi-Clinic where the unknown disease broke out.
A person with the disease suffers from internal and external bleeding, vomiting and feels hot.
On September 12, a critically ill Zambian woman was transferred from Central Lusaka Hospital to Morningside Clinic.
The 36-year-old tourism manager was to be treated for what they believed was tick bite fever. However, she died two days after experiencing flu-like symptoms.
A paramedic who had accompanied the woman from Zambia returned to the hospital on September 27 with similar symptoms. He died four days later.
On Sunday, a nurse who came into contact with the Zambian woman also died while being treated at Sir Albert Robinson Hospital in the West Rand.
Dr Chika Asomugha of the Gauteng health department said they have no idea of what they are dealing with at present.
"Blood samples taken from the deceased were not conclusive of any particular disease.
"We have sent samples to Atlanta in the US for further investigation. We expect the results after 10 days."