A health department investigation found that poor hygiene led to the deaths of six newborn babies at a Johannesburg hospital in May.
"Our investigation showed that the cause of death for all six babies was related to an intestinal virus which is spread by contaminated hands," provincial health boss Qedani Mahlangu told a news conference.
"The cause of death appears to be related to a highly virulent outbreak of gastroenteritis in the premature baby unit," the department's report said.
Mahlangu ruled out negligence among the nurses, saying a chain of events prevented them from meeting hygiene standards.
"In some cases there were not enough washing basins, sanitisers and paper towels," said Mahlangu.
The report identified overcrowding and staff shortages as a major contributor to poor hygiene at the hospital. HIV exposure was ruled out as the cause of infection.
"Our nurses are overloaded, sometimes you find that one nurse is responsible for up to seven newborn babies. That is way higher than the ideal 1:2 ratio," said Mahlangu.
South Africa generally has a high infant mortality rate, with 44 babies dying out of every 1,000 born. That is among the lowest rates in Africa, but very high compared to developed countries. In Sweden the rate is 3.2 per 1,000.
"Hospitals are usually able to fight infection acquired within the wards, but this one just spread like wildfire," said Keith Bolton, one of the investigators who compiled the report.
In a separate case, about 181 newborn babies were reported to have died at an Eastern Cape hospital since the beginning of the year.
Authorities blamed the toll on a number of factors, including HIV complications.