The nursing sister battling a new strain of the arenavirus is still not out of the woods but is making steady progress, a spokesperson at the Morningside Medi-Clinic said on Tuesday.

"She's still very serious, but she is steadily improving," said Melinda Pelser.

"This is a new strain of arenavirus, so it is actually unknown (how long it will take until a full recovery), so the doctors are very cautious. We are just taking it one day at a time."

The sister, whose name hasn't been released for her own privacy, contracted the virus while caring for one of the four people known to have contracted the virus.

Three people died as a result of the virus, and a fourth, a cleaner, had traces of the virus in her body when she died while also afflicted by meningitis.

Sapa