Study: MERS may not become the next SARS pandemic

A foreign worker wears a mask as he rides a bicycle near the King Fahad hospital in the city of Hofuf, some 370 kilometres east of the capital Riyadh, on June 16, 2013. FAYEZ NURELDINE/AFP/Getty Images

Researchers believe that key differences between Middle East respiratory syndrome (MERS) and severe acute respiratory syndrome (SARS) mean MERS might not become the dangerous global pandemic that some have feared.

A new study, published July 25 in The Lancet Infectious Diseases, showed that almost all of the cases of MERS infected people who had other chronic health conditions. On the contrary, SARS infected healthy and unhealthy individuals alike. This could also explain why MERS has a higher mortality rate, because the virus is infecting people who were sicker to begin with.

The research, which is the largest case study of MERS to date, specifically looked at 47 cases (46 adults, 1 child) of confirmed MERS infections that occurred in Saudi Arabia between Sept. 1, 2012, and June 15, 2013.

MERS is a viral respiratory disease that is caused by a coronavirus called MERS-CoV. Coronaviruses are very common, and can range from the common cold to SARS. The first cases of MERS were reported in Saudi Arabia by the World Health Organization in Sept. 2012, and it has been known to spread person to person in some cases.

Patients who are infected with MERS may experience mild to severe acute respiratory illness with symptoms of fever, cough, and shortness of breath. The Lancet study revealed that most of the patients admitted to the hospital had fever (98 percent), cough (83 percent), shortness of breath (72 percent) and muscle pain (32 percent). Twenty-five percent had gastrointestinal symptoms, including vomiting and diarrhea. The researchers also noted that MERS cases progressed to respiratory failure up to five days earlier than SARS.

As of July 21, the World Health Organization has confirmed 90 cases of MERS, including 45 deaths. Patients have been found in Jordan, Qatar, Saudi Arabia and the United Arab Emirates. Additional cases were identified in France, Germany, Italy, Tunisia and the U.K., but those patients had either traveled to the Middle East or became sick in the Middle East and were transferred to another country for care.

The WHO organized an emergency committee to address the potential threat MERS may pose in June.

"We want to make sure we can move as quickly as possible if we need to," WHO flu expert Keiji Fukuda said at a news conference at the time. "If in the future we do see some kind of explosion or if there is some big outbreak or we think the situation has really changed, we will already have a group of emergency committee experts who are already up to speed so we don't have to go through a steep learning curve."

The new study's researcher Professor Ziad Memish, Saudi Arabia's deputy health minister, said in a news release that SARS patients tended to be healthier and younger. Sixty percent of people who passed away from MERS had co-existing chronic illnesses, compared to only 1 to 2 percent for SARS.

A June study in the New England Journal of Medicine determined that MERS has a 60 percent death rate among those infected. But, the Lancet study researchers said that almost all of the patients in their case study had a chronic health condition like diabetes (68 percent), high blood pressure (34 percent), chronic heart disease (28 percent) and chronic kidney disease (49 percent).

"Although this high mortality rate with MERS is probably spurious due to the fact that we are only picking up severe cases and missing a significant number of milder or asymptomatic cases, so far there is little to indicate that MERS will follow a similar path to SARS," Memish said.

The researchers warned that people shouldn't put their guard down about MERS just yet. They noted that because the WHO is finding more mild and asymptomatic cases, this may mean there's more to the disease that researchers may not know.

"The recent identification of milder or asymptomatic cases of MERS in health care workers, children, and family members of contacts of MERS cases indicates that we are only reporting the tip of the iceberg of severe cases and there is a spectrum of milder clinical disease which requires urgent definition," co-author Professor Ali Zumla from University College London, said in a news release. "Ultimately the key will be to identify the source of MERS infection, predisposing factors for susceptibility to infection, and the predictive factors for poor outcome. Meanwhile infection control measures within hospitals seem to work."

So far, no one in the U.S. has contracted the disease, and the risk of it coming here remains low. It is important to note that there are fewer people traveling between the Middle East and the U.S. as there are between the region and Europe. Still, the Centers for Disease Control and Prevention is continuing to monitor suspicious cases.

"The risk is proportionally less in the United States, but we are not assuming the risk is zero," Dr. Mark Pallansch, director of the Division of Viral Diseases at CDC in Atlanta, said to CBSNews.com in late June.

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