A new virus responsible for an outbreak of respiratory illness in the Middle East may be more deadly than SARS, according to a team of infectious disease specialists who recently investigated a set of cases in Saudi Arabia.

Of 23 confirmed cases in April, 15 people died — an “extremely high” fatality rate of 65 percent, according to Johns Hopkins senior epidemiologist Trish Perl, a member of the team that analyzed the spread of the virus through four Saudi hospitals.

Saudi officials said that as of Wednesday, 49 people have contracted the disease and 32 have died.

The infectious disease experts, who published their findings online Wednesday in the New England Journal of Medicine, reported that infection occurred by way of person-to-person contact and poses an especially serious risk because it is easily transmitted in hospital settings.

Worldwide, the overall death rate from the Middle East Respiratory Syndrome Coronavirus — or MERS-CoV — is at 59 percent, according to the Centers for Disease Control and Prevention. That rate is expected to bounce around as new clusters of infection develop.

MERS: Mild for some, deadly for others

The vast majority of MERS-CoV infections have been in Saudi Arabia. No cases have been reported in the United States, but small clusters of infections have appeared in Britain, France, Italy and Tunisia.

Since the virus first emerged in April 2012 with two fatal cases in Jordan, 64 people have been infected and 38 have died around the world. The virus comes from the same family as the severe acute respiratory syndrome (SARS) coronavirus, which killed nearly 800 people worldwide in 2003.

Both viruses have a distinct
haloed appearance when viewed under a microscope, and they typically target the respiratory tract. Like SARS, MERS starts with a fever and mild cough that eventually progress to pneumonia.

At first, MERS does not look out of the ordinary compared with other, less serious types of respiratory infection. But Perl said doctors should start taking careful note of a patient’s travel history, since all reported cases have been linked to Saudi Arabia, Qatar, Jordan and the United Arab Emirates.

The team of specialists mapped the likely trail of infection that spanned four Saudi hospitals in just over a month. Patients stationed in the same hospital room or ward as an infected person, or even taken care of by the same nurse, were likely to be exposed to the virus. Out of the 23 infected, hospital patients made up the majority of cases, but the virus also spread to visiting family members and hospital staff.

The incubation period of the virus — the time between exposure and development of symptoms — was similar to SARS, about five days. During this period, the researchers warned, infection may be possible.

While the high mortality rate is alarming, Perl said that outbreaks tend to have death rates that are high at the beginning but then decline over time as doctors identify patients with milder versions of the illness. She cited the H1N1 and SARS outbreaks as examples.

This particular outbreak was largely contained by early detection and isolation of those infected, and through tighter hospital infection-control procedures — steps such as assigning a specific nurse to watch for patients with symptoms, requiring health-care workers to put on face masks and gloves, and fitting masks on patients.