A 68-year-old South Korean man recently returned from a multi-country trip to the Middle East developed a cough and fever. He visited four health facilities before being diagnosed with MERS (Middle East Respiratory Syndrome), and in the process spread the virus to several more people. Now, 50 people in South Korea have been diagnosed with MERS, and four have died. Two of the patients are healthcare workers.

MERS is a viral respiratory illness caused by a coronavirus (MERS-CoV) and characterized by fever, cough, and shortness of breath; it was first reported in Saudi Arabia in 2012. It has been fatal in 30% of the cases identified, although it’s possible that less-severe cases aren’t being diagnosed and the actual fatality rate is lower. Worldwide, the World Health Organization has been notified of 1,185 laboratory-confirmed cases, and 443 of those people have died. Researchers have detected the virus in camels, but are still investigating how it spreads.

The South Korean government is taking this outbreak very seriously; they have quarantined more than 1,000 people, closed schools, and invited a WHO mission. Although other countries – including the US – have seen individual imported MERS cases in recent years, this is the first outbreak outside of the Arabian Peninsula.

Nonetheless, Nature’s Declan Butler reports that experts don’t consider this outbreak to have pandemic potential. The virus spreads poorly from person to person, and can be controlled by public-health measures; dozens of hospital outbreaks have already occurred in Saudi Arabia. Butler points out that the coronavirus behind the 2003 SARS outbreak – which sickened 8,000 people and killed 774 in 26 countries – had evolved the ability to spread easily between people, while MERS-CoV has not.

Helen Branswell of The Canadian Press (who has written extensively about SARS) also reports that experts consider South Korea’s outbreak similar to what’s been seen so far in Saudi Arabia and the United Arab Emirates. She spoke with infectious disease expert and SARS survivor Dr. Allison McGeer of Toronto’s Mount Sinai hospital; McGeer told Branswell that it’s important to investigate the South Korean outbreak in case something has changed, but, “There’s very good evidence right now from multiple countries in the Middle East that MERS outbreaks are containable.”

Kai Kupferschmidt of Science delves into how a single patient could have led to so many MERS cases in South Korea. Most of the cases have been tied to St. Mary’s Hospital in Pyeongtaek, where bad ventilation in patient zero’s hospital room likely played a role in virus transmission. Kupferschmidt writes:

Bad ventilation alone would hardly explain the catastrophic spread seen in the hospital, says Christian Drosten, a virologist at the University of Bonn in Germany. But if there was bad ventilation plus a patient shedding a greater than usual amount of the virus, it could make a difference. In a study of dozens of MERS patients in intensive care in Saudi Arabia, for example, some had a much higher virus load in their exhaled breath than others, he says. “This must have been such a patient.” In combination with the constant circulation of the air in the room, this could help explain the high number of infections, Drosten says.

“A highly infectious case, combined with poor infection control can easily lead to this kind of cluster,” says Mike Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, Twin Cities. That that combination happened in Seoul was just bad luck, he says. “This could happen just as well in New York or Berlin.” But the government in South Korea did botch the initial response, he says. “There was no reason to close those schools, for instance. And distributing patients over many hospitals probably helped the virus spread,” he says. “But I think they are starting to get it right.”

If a single “superspreader” patient arrives at a hospital with poor infection control, dozens of cases, and even several deaths, can result. The European Centre for Disease Prevention and Control (via Avian Flu Diary) emphasizes the need for hospital vigilance:

The importance of eliciting a travel history from patients with severe respiratory disease cannot be overemphasised. The immediate, systematic and strict implementation of infection prevention and control measures in the hospital setting are essential to interrupt transmission and prevent clusters of healthcare-associated infection. Furthermore, the challenges of detecting rare imported cases of respiratory infection early on highlight the need for adequate infection prevention and control measures for all patients showing symptoms of acute respiratory infection.

WHO recommends that probable and confirmed cases should be admitted to adequately-ventilated single rooms or airborne precaution rooms. Healthcare workers caring for probable or confirmed cases of MERS-CoV infection should use contact and droplet precautions (medical mask, eye protection – i.e. goggles or face shield – gown and gloves) in addition to standard precautions. Airborne precautions should be taken when performing aerosol-generating procedures.

In the US, CDC offers MERS guidance and a preparedness checklist for healthcare providers.