RIYADH — Saudi Arabia has identified 18 new cases of Middle East Respiratory Syndrome (MERS), it said late on Wednesday, pushing the total number of infections in the country so far to 449.Four people died from the disease on Wednesday, taking the total death toll in Saudi Arabia to 121 since MERS, a form of coronavirus, was identified two years ago, the Health Ministry said in a statement on its website.The rate of infection in Saudi Arabia has surged in recent weeks after big outbreaks associated with hospitals in Jeddah and Riyadh. The total number of infections nearly doubled in April and has risen by a further 21 percent already in May.The World Health Organisation said on Wednesday the hospital outbreaks had been partly due to "breaches" in recommended infection prevention and control measures, but added that there was no evidence of a change in the virus's ability to spread.Scientists around the world have been searching for the animal source, or reservoir, of MERS virus infections ever since the first human cases were confirmed in September 2012.