Of all the questions that scientists hope to answer about the new coronavirus that sweeps the world, the most pressing is this: how deadly is it?
The only way to know is to find out how many people have been infected – and that is the real challenge.
Over 40,000 infections have been confirmed, but experts are sure there are at least tens of thousands more. Some cases were not counted because the patients did not have biological samples sent to a laboratory. Some never went to see a doctor and others had symptoms so mild that they didn't even know they were sick.
Without a true picture of the total number of cases, it is impossible to calculate a mortality rate. That is why dozens of epidemiologists and mathematicians are working to solve one of the most complex modeling problems of their time.
Situation reports World Health Organization provide an upper limit on the mortality rate. As of Tuesday, there were 43,103 laboratory confirmed infections worldwide, resulting in 1,018 deaths. A little simple arithmetic indicates that just over 2% of these infections were fatal.
But since the current infection count is very low, that death rate – formally known such as a "case mortality rate" or "case mortality rate" – is very high.
"It's something we can say for sure," he said Josh Michaud, who was an infectious disease epidemiologist at the Department of Defense during the 2009 H1N1 flu pandemic.
Dr. Nancy Messonnier, director of the National Center for Immunization and Respiratory Diseases at the Centers for Disease Control and Prevention, said the 2% death rate "has been relatively stable" so far in the outbreak. "But whether this is really a real fatality rate or not, I don't think we have the information right now."
Funeral workers disinfect themselves after dealing with a coronavirus victim in Wuhan, China.
(Chinatopix via the Associated Press)
When an outbreak involves a virus never seen before, there are no shortcuts that epidemiologists can take to determine how many people became ill and how many died. They need to look at a variety of sources to see how many coronavirus deaths have been attributed to other causes by mistake and vice versa. They also need to find out how many infected people have never interacted with the medical system.
Researchers at Imperial College in London modeled the spread of the infection based on the number of confirmed cases and the flow of travelers in and out of Wuhan, China, before the quarantines took effect. The team assumed that the virus had an incubation period of five to six days before symptoms appeared and that infected travelers were detected when they arrived at their destinations.
The result was a case count between 1,000 and 9,700 on January 18, the date the official record number of infections was below 300. Uncertainties in the model resulted in a wide range of errors, but the actual number of people infected was probably around 4,000, the team reported.
A doctor talks to a patient during an online consultation session at a hospital in northeast China's Liaoning province.
(STR / AFP via Getty Images)
WHO is creating its own research consortium to investigate the original source of the new coronavirus strain and how easily it spreads. By improving these parameters, WHO can make its models more accurate.
"The more time you have, the more evidence you have to work with, the better your estimate will be," he said. Dr. Carlos del Rio, a global health epidemiologist at Emory University.
A good outbreak model is a lot like an iceberg, he said Marc Lipsitch, an infectious disease epidemiologist at the Harvard T.H School of Public Health.
The tip of the iceberg – the part you see – is the patients who die. This is the easiest number to assess for the simple reason that deaths are hard to miss.
All other infected people are part of the iceberg that is under water. Epidemiologists divide them into layers.
Just below the surface are patients who are sick enough to be hospitalized. Below them are patients who seek basic medical attention. The next level is made up of people who take care of their illnesses at home and the last is people who have no symptoms.
In 2009, when Lipsitch was helping the CDC to determine the severity of the H1N1 flu, he and his fellow researchers recognized that no single data source could capture all five layers. They then gathered surveillance data from various parts of the U.S. health care system and gathered it to generate their iceberg model.
A hospital worker in Chicago wears a mask during the H1N1 swine flu outbreak.
(Antonio Perez / Chicago Tribune)
An important contributor was the New York City Department of Health and Mental Hygiene. Employees did not try to count everyone who was infected. Instead, they focused on carefully documenting all patients who were hospitalized. Thanks to this precision, the researchers were able to determine the relationship between hospitalizations and deaths.
Meanwhile, in the much smaller city of Milwaukee, there were not enough deaths to make statistically significant calculations. Instead, the authorities decided to count all H1N1 patients who were seeking some form of medical care. His records allowed researchers to assess the relationship between visiting a primary care physician and being admitted to a hospital.
At the CDC, workers conducted telephone surveys to ask people if they had experienced flu-like symptoms at the time the outbreak began in April and May and, if so, whether they had consulted a doctor. (Luck was on their side, Lipsitch said, because anyone with a flu-like illness in the spring almost certainly had the new H1N1 strain, since the seasonal flu had subsided. That's not the case this time, since the coronavirus took off during the flu season.)
Within eight months, scientists had a reliable model of the H1N1 virus that included everyone except those who were infected without realizing it. To count them, the researchers would need to collect blood samples from randomly selected members of the public and test them for H1N1 antibodies, a sign that the person had been exposed and their immune system had responded. But these tests were time-consuming and expensive to justify.
"The worst-off patients are more likely to seek medical attention and be diagnosed," said Messonnier.
In the early days of the H1N1 flu pandemic, attributed to pigs in Mexico, it appeared that 10% of those infected were dying from the flu. Health professionals have identified a series of infections so mild that people have not even seen a doctor. Once these cases were taken into account, the death rate fell below 0.1%, said Lipsitch.
"In the end, this flu was no more deadly than the common seasonal flu," said Michaud.
There is another reason why experts think the coronavirus case count is disabled: missing data.
Whether they recognize it or not, the outbreak has Chinese health workers needing time and resources. Workers may not have the bandwidth to keep records of patients with mild infections, even if they belong to the total case count, said Michaud. There are also no test kits available to diagnose all patients who they suspect are infected. Even the death toll – the most reliable number – can be very low.
Patient samples are ready to be tested for the new coronavirus strain in a laboratory in Wuhan, China.
(STR / AFP via Getty Images)
Experts also suspect that Chinese officials are withholding data that may be embarrassing for them, such as the number of medical workers who have died so far.
"We need to bring this virus to light so that we can attack it properly," he said. Adhanom Ghebreyesus Tedros, director-general of WHO.
Another complicating factor is that death rates from infection can vary across the world. Disparities in the quality of health care are exacerbated in an outbreak, when people and resources are pushed to the limit.
"The shortage will certainly cause more deaths in Wuhan," said Del Rio. Meanwhile, if a few dozen patients "showed up in Atlanta, they would be treated to luxury."
Infection patterns outside China will be more useful to health officials around the world than any data from Beijing. The behavior of the virus in the other 27 countries and territories that own it will provide a better picture of its typical severity – and what would happen if it started to spread in the United States.
Scientists are not ruling out the possibility of the virus evolving in a way that makes it more lethal or that helps it spread from person to person (or both). But they point out that it would not be in the interest of a virus to kill its host before it spreads to a new one.
At this point, the new coronavirus appears to have more in common with the common flu than with exotic diseases like Ebola or the Middle East Respiratory Syndrome (MERS), both with mortality rates around 40%. Among a group of 17,000 people with confirmed coronavirus infections, 3% were classified as critical, 15% had severe infections and 82% were mild, he said. Dr. Maria Van Kerkhove, acting head of emerging diseases at WHO. Of the 2% who died, many were elderly people with underlying health problems that made them more vulnerable.
"We can say with great confidence that this is not killing people back and forth," said Del Rio.
A 2% mortality rate may seem low, but it is high enough to cause real damage in the worst case scenario where the virus is not stopped.
"If you can't contain the spread, all bets are off," said Del Rio. "Two percent of China's population – 28 million people – is still quite high. And 2% of the world?