With few data available, experts are at a loss to explain the rising tide of MERS-CoV (Middle East respiratory syndrome coronavirus) cases in Saudi Arabia and the United Arab Emirates (UAE). But when it comes to speculation, two leading possibilities mentioned are a change in the virus and a seasonal pattern to its transmission.

Saudi Arabia has reported more than 100 cases since the beginning of April, many of them in a healthcare-related outbreak in the Red Sea port of Jeddah. The number of recent cases in the UAE, meanwhile, is unclear but seems to be well above 25, including 14 that, according to the World Health Organization (WHO), stemmed from one healthcare worker (HCW).

In a statement today, the WHO noted that about 75% of the recent cases are secondary ones resulting from human-to-human transmission, with the majority occurring in healthcare settings, often in HCWs. Acknowledging “critical information gaps,” the agency said it is unaware of what specific kinds of exposures have sparked the cases in healthcare facilities.

Experts are quick to emphasize that very little is known so far about the outbreaks in Saudi Arabia and the UAE, making it impossible to reach any conclusions about their cause as yet.

“These cases are just being reported and information regarding them is trickling in to WHO,” said David Swerdlow, MD, leader of MERS activities at the US Centers for Disease Control and Prevention (CDC). “As we learn more, we can get a sense of the nature of these newly reported cases. For example, is this just seasonality, an increase in cases because of a hospital outbreak or a change in the efficiency of how the virus is transmitted?

“At this time, there is no conclusive indication the virus has adapted enough to sustain human-to-human transmission, something CDC is monitoring closely,” he added.

Possibility of viral evolution

Allison McGeer, MD, a microbiologist and infectious diseases consultant at Mt. Sinai Hospital in Toronto, agrees that there is too little information to do more than speculate for now, but she sees some signs that suggest the possibility that the virus is changing. She was part of a team that traveled to Saudi Arabia last year and advised the government about its response to MERS-CoV.

In an interview, McGeer, who led efforts to stop the SARS (severe acute respiratory syndrome) coronavirus outbreak in Toronto in 2003, compared the Jeddah outbreak with the outbreak in Al-Ahsa (also written Al-Hasa) in eastern Saudi Arabia a year ago. That one involved 23 confirmed and 11 probable cases in several hospitals, according to a June 2013 report in the New England Journal of Medicine (NEJM).

McGeer said that although information is lacking, the Jeddah outbreak “seems like a multi-institutional, really complicated outbreak. . . . It’s clear that there are a substantial number of healthcare workers involved.”

But the two outbreaks, she said, seem to differ in at least one way: “Compared to last year, the attack rate in healthcare workers appears to be higher, and I don’t think that that is related to more testing. One of the striking things about the Al-Hasa outbreak was that the attack rate in healthcare workers was relatively low compared to the rate in patients.

“This ratio of healthcare workers to patients looks different now, and that raises the issue of whether the virus is changing,” she added. “To me that’s the critical issue that needs to be answered.”

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