Infectious disease watchers are again wondering what is going on in Saudi Arabia. Since the beginning of February the Saudis have reported 52 cases of Middle East respiratory syndrome—better known as MERS; 40 have come to light in the past week or so alone. Since the disease first hit the world’s radar in September 2012 only two months have racked up more cases than this one has. They were April and May 2014, when Saudi Arabia had rampant MERS outbreaks in several hospitals.*

An expert delegation from the United Nation’s human and animal health agencies began a three-day mission to the Arabian Peninsula’s geographically largest country Wednesday, trying to get to the bottom of why MERS cases are soaring.

This is the time of year in which the number of MERS cases has climbed in the past, although not enough time has elapsed to make clear whether that pattern will continue. In the past two springs large hospital outbreaks in Saudi Arabia have certainly created the appearance of a high season for MERS transmission, which some scientists believe exists and is linked to the birth and weaning of young camels. The animals are known to be susceptible to the virus and can transmit it to people. Like young children who infect the adults around them with colds and flu, juvenile camels are thought to drive the spread of this virus among camel herds and out into the human population. Then someone becomes sick enough to require hospitalization and the infection spreads.

But even if there is a seasonal component to MERS, a spring surge has never before started this early in the year. By comparison, in the past two Februaries fewer than 10 cases were reported. "Of course we don't have 10, 20 years’ history to be able to predict any seasonal patterns,’’ says Peter Ben Embarek, a food safety expert who is the World Health Organization’s point person for MERS. “But just based on the last couple of years, the couple of seasons we've come through, it's not a good start."

Embarek is one of about a dozen people on the international delegation that is traveling to Saudi Arabia. The group includes officials from WHO; the Food and Agriculture Organization of the U.N.; and the World Organization for Animal Health (known by its French acronym, OIE). It is hoped that having both human and animal health officials involved will enhance cooperation on the problem between the ministries of health and agriculture in the Saudi capital, Riyadh.

Dutch virologist Marion Koopmans, who has led studies trying to illuminate the role camels play in the dynamics of the disease, calls the recent swell of cases remarkable. Koopmans notes, though, that part of the increase might be due to the fact the Saudi Ministry of Health now appears to have a more systematic approach to finding and reporting cases.

Answering the question of how people are getting infected will be job one for the delegation. According to the daily updates posted online by the Saudi health ministry, most of the recent cases—unlike during past surges—did not report contact with camels or with other people infected with MERS—either in the community or in a hospital setting. “It seems quite a few are not health care associated,” says Koopmans, who is head of the viroscience department at Erasmus Medical Center in Rotterdam. “First priority is to find out if that is real, which is what the mission no doubt will try to find out.”

Scientists generally rely on so-called case-control studies to tease out how people contract a new disease. Such studies are designed to examine in minute detail the behaviors and exposures of people who become infected and compare them with similar people who did not become sick. If they are done correctly, a picture should come into focus: For example, in a salmonella outbreak all the sick people ate sprouts at the salad bars of a certain restaurant chain but none of those who were not sick did.

For over two years Saudi Arabia has ignored repeated pleas from WHO and others to conduct a case-control study. But now the Geneva-based global health agency has been told the Saudis have done this critical research. Details of how the study was designed and what its findings show have not yet been disclosed. The country’s snail’s pace in trying to find the source of the infection has puzzled many outsiders. But Ben Embarek says at least part of the reticence is likely cultural. In this part of the world it is not common practice to ask personal questions—or to answer them if they are posed. "People tend to be...not terribly precise in the way they answer. They don't understand what is expected,” he says.

There have been close to 1,000 confirmed cases of MERS since the new disease was first detected, with nearly 900 reported by Saudi Arabia. Roughly 37 per cent of individuals with confirmed infection have died from the ailment, which can be mild but often provokes severe respiratory illness. The disease is caused by the MERS coronavirus, a cousin of the virus that sparked the 2003 SARS outbreak. But where SARS quickly spread from its epicenter—southern China—to ignite outbreaks in Hong Kong, Vietnam, Toronto and other locations, MERS has principally leveled its damage close to home. Most of the cases have been diagnosed in countries on the Arabian Peninsula. There have been a few exported cases found in countries in North Africa, Europe, Asia and even North America. Last year two physicians who work in Saudi Arabia but have ties to the U.S. brought the virus to Indiana and Florida. But so far these exported cases have not triggered a SARS-like seeding of outbreaks elsewhere. Still, no one can rule out that possibility.

A recent case highlights the concern. Earlier this month a nurse who had been working in Saudi Arabia became ill after traveling home to the Philippines. She spent several days in hospital before doctors thought to test her for MERS, by which point a number of people had been exposed to her. Fortunately none has tested positive to this point. Ben Embarek says the months-long battle to contain west Africa’s Ebola outbreak has overshadowed MERS and may have led some countries to forget this threat. But nations should not let down their guard, he says. “These types of cases popping up in other countries should be investigated and countries should be making sure that their surveillance system is set up to pick up this type of situation."

Meanwhile another infectious diseases expert worries that the world appears to have forgotten an important lesson from SARS—the need for scientists from different countries to work together to address problems like MERS. “It still appears to me that there are only one or two groups from outside the region that are working on this virus,” says Trish Perl, an infection control expert from Johns Hopkins University who traveled to Saudi Arabia to help contain a MERS hospital outbreak two years ago. “If that is the case,” she adds, “we are missing a huge opportunity to understand an emerging disease. One of the remarkable stories around SARS was the scientific collaboration that occurred and how that helped us define the SARS epidemiology.”

*Editor’s Note: Thanks to Maia Majumder for access to her MERS epicurve.