Saudi Arabia announced Wednesday five new deaths from MERS, raising the death toll in the country worst-hit by the mysterious coronavirus to 157 since it appeared in 2012.
The health ministry also reported 16 new infections with Middle East Respiratory Syndrome raising the total so far to 511.
Three women, all over 60, died in Riyadh, while two men, aged 56 and 57, died in the port city of Jeddah, the ministry said on its website.
Saudi Arabia accounts for by far the largest proportion of the 571 MERS cases worldwide reported to the World Health Organisation, 171 of which have proved fatal.
MERS has also been found in 16 other countries but nearly all have among people from, or who had recently travelled to, the Gulf.
Research has identified camels as the likely original source of the virus and the Saudi agriculture ministry on Sunday urged camel handlers to wear masks and gloves.
But a growing number of infections have been among health workers or fellow patients in hospitals treating MERS cases and the WHO called on Wednesday for improved infection control.
A WHO team carried out a five-day inspection visit to Saudi Arabia earlier this month and pinpointed breaches in its recommended infection prevention measures as being partly responsible for the spike in hospital infections.
A rash of cases among staff at Jeddah's King Fahd Hospital last month sparked public panic and the dismissal of its director and the health minister.
MERS is considered a deadlier but less transmissible cousin of the SARS virus that appeared in Asia in 2003 and infected 8,273 people, nine percent of whom died.
Like SARS, it appears to cause a lung infection, with patients suffering coughing, breathing difficulties and a temperature. But MERS differs in that it also causes rapid kidney failure.