SEOUL, South Korea — South Korean officials recorded nine new cases of Middle East respiratory syndrome overnight to Saturday, bringing the total number of infections to 50 as it ruled out a possible mutation of the virus.

The Health Ministry also announced that the wife of the first MERS patient who was also infected with the virus had recovered and been released from the hospital. Her husband, a 68-year-old who was found to be infected after returning from a Middle East trip in May, is also recovering.

All subsequent confirmed cases of the virus in hospital staff, patients and relatives can be traced back to him.

Four people have so far died from the MERS outbreak in South Korea. About 1,600 people remain under quarantine.

On Friday, the World Health Organization said there was no evidence of airborne transmission or sustained human-to-human transmission of the virus in communities. It did, however, caution that MERS, first identified in 2012 in Saudi Arabia, was a relatively new disease and that “information gaps are considerable.”

An analysis of the genome showed no difference from the strain originating in the Middle East, the Health Ministry said.