(CNN)Here's some background information about MERS, or Middle East respiratory syndrome.
MERS is a viral respiratory illness brought on by Middle East respiratory syndrome coronavirus (MERS-CoV). It is in the same family of viruses as SARS (severe acute respiratory syndrome) as well as the common cold.
The illness was first reported in Saudi Arabia in 2012.
Researchers don't yet know its exact mode of transmission, but it has spread through close contact with people who are ill. It is thought to spread through respiratory secretions, like coughing. MERS does not spread easily between humans.
The virus may have first transferred from an infected animal to a human. A 2014 study indicated three-quarters of camels in Saudi Arabia tested positive for past MERS exposure and at least one bat had the illness.
According to the Centers for Disease Control and Prevention, the incubation period for MERS, from exposure to symptoms, is two to 14 days.
Since September 2012, there have been at least 2,494 laboratory confirmed cases and at least 858 deaths worldwide. Cases have been confirmed in 27 countries (as of November 2019).
Symptoms include fever, cough, shortness of breath, kidney failure and gastrointestinal issues. Not all those infected are symptomatic.
There is no vaccine and no recommended antiviral treatment.
The mortality rate for reported cases is about one third.
South Korea and China outbreak 2015
Total confirmed cases: 186
Korea: 185 cases, 36 deaths
China: 1 case, 0 deaths
September 2012 - Health officials confirm the first case of a novel coronavirus (nCoV) in Saudi Arabia.
November 2012 - An investigation into an April outbreak of acute respiratory illness in a Jordanian hospital reveals that two people who died were infected with the novel coronavirus. An additional 13 people had symptoms of the disease.
February 2014 - Scientists find evidence of MERS-CoV in 74% of the single-humped camels (dromedaries) in Saudi Arabia.
April 29, 2014 - Researchers isolate live MERS virus from two single-humped camels. One of the substrains found matches a substrain isolated from a human patient.
May 2014 - The CDC announces the first US cases of MERS. The two patients, one in Indiana and another in Florida, are both health care workers who live in Saudi Arabia and have traveled to the US.
May 2015 - A MERS outbreak begins in South Korea. "Patient Zero" returns to South Korea on May 4 after traveling to countries in the Middle East, develops symptoms and is confirmed infected on May 20.