She and two colleagues pored over hospital records, tracking the spread of Middle East Respiratory Syndrome, or MERS, just as they did with a SARS outbreak in Toronto nearly a decade earlier.
The researchers "were looking for any crossover to explain how one person gave it to another," Perl said. They traced a web of infection linking a man and his son to nearly two dozen others who had tended to the sick, visited the same health care facilities or were in adjacent hospital beds.
Their findings appear Wednesday in The New England Journal of Medicine, shedding new light on the spread of an outbreak that has reached three continents with what researchers called "worrisome" mortality.
There have been no cases in the United States, but health officials are preparing for the possibility and the federal Centers for Disease Control and Prevention has called on hospitals and health officials to be alert for possible cases.
MERS and SARS are types of coronaviruses, a class that includes mild upper-respiratory infections such as the common cold. MERS, which appears as a severe cough, fever and shortness of breath, has been confirmed in 64 people in the Middle East, Africa and Europe in the past year, killing 38.
Its spread to Europe is causing increased alarm that it could become a global disease. SARS, or severe acute respiratory syndrome, sickened more than 8,000 and killed 774 worldwide in a 2003 outbreak.
The new research on MERS ensures that preparation will include an emphasis on preventing the disease from spreading in hospitals and other health care settings, doctors said.
"They show there are chains of spread of the virus, from person to person to person to person, which had not been identified previously," said Dr. Matthew Frieman, an assistant professor at the University of Maryland School of Medicine who also is studying MERS. "The parallels with SARS are becoming more and more obvious now."
However, relatively little is known about MERS. It is not clear how the first human cases originated — the virus' genome shows links to bats — and there is no known treatment.
Perl and colleagues Dr. Allison McGeer of Mount Sinai Hospital in Toronto and Dr. Connie Price of the University of Colorado, Denver were among the teams of researchers tracing the 2003 SARS outbreak that sickened more than 250 people in Toronto.
A deputy minister of health from Saudi Arabia was on the other end of the line when Perl, senior epidemiologist for the Johns Hopkins Health System, answered her phone on a recent Sunday, and she agreed again to join an investigation.
After flying halfway around the world last month and being shuttled across the desert in an SUV, the researchers visited a hospital where the outbreak was centered. Armed with pages of patient records, they worked in a hotel lounge to "put a story together," Perl said.
What they found was a complex chain of connections. They examined the timing and proximity of possible contact among the infected.
In an early instance, they found the illness had spread to nine patients who visited the same outpatient dialysis center. Confirmed cases were later found in seven others who were patients, family members or health care workers who came in close contact with those nine.
They found that a single patient had transmitted the infection to seven others, while another passed it to three people and four others to two people apiece. The mortality rate in the pool of patients they examined was an alarming 65 percent. They estimate the actual mortality rate is lower. Among confirmed and suspected cases, the rate is about 55 percent.
Perl passed the data on dates and times of contact to Derek Cummings, an associate professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health. He determined the incubation period of the disease to be about five days, and found that 95 percent of infected patients could be expected to show symptoms within 12 days.
That information can inform response to the outbreak and shows the need to quarantine patients to prevent further spread of the disease.
"Our investigation underscores the importance of infection-control measures for this class of coronaviruses," Cummings said. "I think you just have to be hyper-vigilant to stop these coronavirus outbreaks in health care settings."
The CDC is stressing that risk and has developed diagnostics and is distributing test kits to ensure that state and local health officials can accurately diagnose any U.S. cases.
Maryland health officials received the materials last month and have not had to use them, said Robert Myers, director of the state public health lab.
"The reason we are taking this very seriously is Europe has already experienced at least four distinct episodes of importation" from the Middle East, said Dr. Mark Pallansch, director of the CDC's viral diseases division. "These episodes tell us the risk is not zero. We have to expect that an importation could occur, and we need to be prepared for that eventuality."
The disease is just the latest infectious outbreak keeping Perl busy. She said she is pulled into such investigations around the world every couple of years, along with visiting hospitals around the country with infection problems.
She has spearheaded or been involved in recent investigations into the national outbreak of fungal meningitis linked to tainted steroid injections and annual flu outbreaks. When dozens of workers got sick at the Johns Hopkins at Keswick offices in Hampden in February, they were asked to cooperate with Perl's inquiries to determine the source of the illnesses.
There is still much to be learned about the MERS outbreak, she said. For example, while the study found that nearly two out of three people infected with the disease died, it is possible that milder cases might have gone undetected.
"There's no question it's a fact, but I don't know whether it's reality," Perl said.
The disease: Middle East Respiratory Syndrome is a virus similar to SARS that causes upper respiratory tract infections, thought to be passed via coughing
Case count: 64 infections and 38 deaths across eight countries in the Middle East, Europe and Africa
Symptoms: Severe acute respiratory illness with cough, fever and shortness of breath
Prognosis: Deadly in 65 percent of those infected as part of a cluster in Saudi Arabia that was the subject of a study in The New England Journal of Medicine
Response: With no known treatment, health officials are focusing on preventing spread of disease within health care settings, recommending quarantining patients and preventive measures such as wearing masks and glovesCopyright © 2015, The Baltimore Sun