MERS Surge Remains Unexplained

The dramatic increase in Middle East Respiratory Syndrome (MERS) coronavirus cases in late March and early April of 2014 raises troubling questions.

MERS shares characteristics similar to severe acute respiratory syndrome (SARS) coronavirus. But while its genes have been sequenced and tests for infection created, the natural history of the disease remains unclear, and there is no specific treatment or vaccine. In the early months of the MERS outbreak, the virus had a very high case-fatality rate that is still hovering around 30%, despite an increased number of confirmed cases without symptoms. In the early stages, about 15 cases were reported each month. But more than 250 cases have been reported by the Kingdom of Saudi Arabia (KSA) since March 22, more than half of the 421 cases reported to date.

According to the World Health Organization (Geneva, Switzerland), the sweeping surge in MERS cases, especially among healthcare workers, appears in large measure to be due to problems with infection control practices in some KSA hospitals. This appears to mirror a similar trajectory as SARS, which also spread well in hospitals. About 20% of the roughly 8,500 SARS patients identified were health-care workers, and people in hospital for other health ailments also made up a substantial portion of SARS sufferers.

Another factor implicated is that a recent change in KSA policy of who to test for MERS infection—i.e., not just sick people, but seemingly healthy contacts as well—is also inflating the country's MERS tally. This testing change is identifying significant numbers of people who are infected, but have mild or no apparent symptoms. But while the steep climb in cases alone is a cause for concern, a more serious problem is that KSA and the United Arab Emirates (UAE) have been exporting MERS cases.

Malaysia, the Philippines, Jordan, Egypt, and Greece have all recently reported diagnosing MERS in people returning from Saudi Arabia or the UAE. In April 2014, the United States disclosed it had found its first MERS case, a US citizen who lives and works in the health-care sector in the KSA capital of Riyadh. And with Ramadan—the Muslim month of fasting—starting at the end of June, the potential for exported cases among the hundreds of thousands of Hajj pilgrims is considerable.

“The Saudis themselves are extremely aware of the issues, and so they're very conscious that they want to make sure that people coming to visit and people leaving are not either posing a danger to other pilgrims in Saudi Arabia or not spreading infection to the rest of the world,” said Keiji Fukuda, MD, a senior WHO official. “I think they're very conscious about that, and very responsible about that. But it's a difficult situation, because people want to go on pilgrimages. So balancing all of those things requires some careful thinking and discussion about how to get that balance right.”

Recent studies support a theory that camels serve as the primary source of the MERS coronavirus infecting humans, while bats may be the ultimate reservoir of the coronavirus. Evidence includes the frequency with which the virus has been found in camels to which human cases have been exposed, serological data which shows widespread transmission in camels, and the similarity of the camel coronavirus to the human coronavirus.

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World Health Organization