A German coronavirus expert says the virus responsible for the MERS infection appears not to have changed.
Dr. Christian Drosten says based on what his laboratory has seen so far, this month's surge in MERS cases cannot be explained by mutations in the virus.
Drosten's lab at the University of Bonn has been looking at genetic sequences of RNA drawn from samples from 30 recent cases from Jidda, Saudi Arabia, where the largest increase in cases has occurred.
In an email, Drosten says the lab has sequenced three nearly full genomes and they see no signs of significant changes that could account for the increase in cases.
Earlier work on the samples showed no major changes in any of sequences, though at that point only a small part of the genome of each had been sequenced.
Drosten says the increase in cases may be due to infection control problems in hospitals where the virus has spread as well as milder cases coming forward as the public has become more aware of and concerned about MERS.
This is the first analysis of MERS viruses from cases that have occurred in 2014 and fills an important information gap.
The number of new cases has spiked sharply this month, leaving experts worried about the possibility that the virus might have become more transmissible among people.
There have been as many cases reported so far this month as in the 24 previous months combined. The earliest known cases of MERS occurred in April 2012.
On Saturday, Saudi Arabia reported an additional 10 cases and two deaths, bringing their total to date to 323 cases, 94 of which have been fatal.
Most of the April cases have been reported by Saudi Arabia, but there has also been several dozen cases in the United Arab Emirates.
In total, affected countries have reported just over 400 cases to date.
On Saturday authorities in Egypt said they had diagnosed their first MERS case, in a man who had recently been in Riyadh, Saudi Arabia.
People infected with MERS have recently travelled from Saudi Arabia and UAE to Malaysia, the Philippines, Jordan and Greece. To date there is no evidence any of those people spread the infection to others in those countries. The Malaysian man, who was a religious tourist to Mecca, died from his infection.
In a risk assessment issued Thursday, the World Health Organization warned more exported cases are "very likely" to occur in travellers, religious pilgrims and foreign nationals who work in affected Middle Eastern countries. It urged countries to be on the lookout for MERS cases.
Mounting evidence suggests that camels are the source of the virus, but it is not yet known how people are contracting it.