A man in a Saudi hospital has pneumonia. The patient in the room next door gets sick, and before anyone realizes what is happening he infects seven others, each of whom infects at least one more.An outbreak is born.

The MERS virus


A detailed investigation of the viral illness first detected last year in Saudi Arabia has revealed the chilling ease with which the virus can spread to ill patients in the hospital — and its ability to infect some close contacts like hospital staff and family members who were in good health. A report on the investigation published Wednesday in The New England Journal of Medicine pinpointed the time it takes for a person to get sick after being exposed to the virus, a median of 5.2 days.

The disease has now infected 64 people and killed 38 in eight countries. Saudi Arabia has had the most cases. The United States has had none.

The disease was first recognized in Saudi Arabia last September, and was later named MERS, for Middle East respiratory syndrome. It is caused by a coronavirus, a relative of the virus that caused SARS (severe acute respiratory syndrome), which originated in China and caused an international outbreak in 2003 that infected at least 8,000 people and killed nearly 800.

MERS has not spread as rapidly or as widely as SARS did. The first few MERS cases seemed to pop up sporadically and mysteriously, and at first doctors did not think the disease was contagious. But over time it became apparent that patients in hospitals could infect one another, and that family members and health workers could sometimes contract it, too.

The apparently high death rate from the disease has worried health experts. More than half of the confirmed cases have been fatal. However, it is possible that milder cases have gone undetected and that the disease is not as deadly as it may initially appear, said Dr. Trish M. Perl, an author of the new report, and a senior hospital epidemiologist and professor of medicine at Johns Hopkins University, who traveled to Saudi Arabia to investigate the outbreak.

But Dr. Perl added: “I’m very concerned about the amount of transmission we’ve witnessed in health care facilities, and the severity of disease we witnessed. And you’re helpless. There’s nothing to offer these patients.”

Dr. Perl, who also helped track the SARS outbreak in Toronto, said the new disease was very much like SARS, “almost scarily close.”

One patient infected seven others, somewhat reminiscent of the SARS phenomenon in which some patients were “superspreaders” who infected dozens of other people. But it is too soon to tell whether that kind of transmission will continue to occur with MERS, Dr. Perl said.

Doctors are trying antiviral drugs, but there is no proven drug treatment and no preventive vaccine. There is no rapid diagnostic test for people with symptoms; testing must be done at specially equipped labs. Nor is there a reliable test to determine whether people were exposed in the past, something that would help determine how widespread and severe the infection is.

Although many experts say global health authorities have gotten much better than in the past at detecting and investigating sudden disease outbreaks, Dr. Perl said they still were not responding quickly or effectively enough.

“It’s déjà vu,” she said. “How many times do we have to do this before we start having surveillance strategies to protect ourselves? Have we lost our way? This has been dragging on since September. There’s been a lot of wringing of hands. We haven’t learned from our past mistakes.”

So far, according to the World Health Organization, all the cases have originated in Jordan, Qatar, Saudi Arabia or the United Arab Emirates. Four other countries, Britain, France, Italy and Tunisia, have found cases in returning travelers and their close contacts.

In May, Saudi health officials invited Dr. Perl and a team of international experts from Britain, Canada and the United States to help study the outbreak. The team focused on 23 cases that occurred from April 1 to May 23 in four hospitals in Al-Hasa, an eastern province of Saudi Arabia. So far, 15 of the patients have died.

Team members visited the hospitals and pored over medical records to map the path of the virus. Most of the cases occurred in people who had other underlying illnesses and shared hospital rooms or wards with patients who had MERS. But several cases occurred in relatives who visited them, or hospital workers caring for them.

Although the new disease spread in hospitals, it did not arise there. The first cases came from people who were exposed elsewhere, perhaps through foods or animals. But researchers still do not know the source of the MERS virus or how the first patients contracted it — information essential for telling people how to avoid it.

The SARS virus is thought to have originated with bats, and scientists suspected that the same might be true of MERS, and that people might have contracted it from eating dates that had been contaminated by bats. But so far, no bats or any other animals have been found to be infected, according to Dr. Alimuddin I. Zumla, an author of the study and a professor of infectious diseases and international health at University College London Medical School.

“They have looked at over 200 animal species in the kingdom, thousands of samples from bats, cats, camels, other animals,” Dr. Zumla said. “Unfortunately, at the moment there is no link.” He said air-conditioning systems and water supplies were also being checked.

More than twice as many men as women have contracted the disease. Researchers do not know why.

“I don’t think the virus prefers any gender,” Dr. Zumla said, adding that he suspected that Saudi women might be protected by their veils, which cover their mouths and noses and might help keep the virus out.

Health officials are not recommending travel restrictions, but Dr. Zumla said that Saudi health officials had begun screening visitors for symptoms of the disease, like runny noses, coughs and fever.

He said health experts would be increasingly concerned as the time nears for the annual pilgrimage of Muslims to Mecca.

“Four million pilgrims from 182 countries are coming to Saudi Arabia in two months’ time,” Dr. Zumla said. “I am worried, as a physician.”