Health officials in China, racing to try to contain a fast-growing coronavirus outbreak, are principally recording severe cases of disease, using a case definition that cannot capture patients with mild illness, according to experts familiar with the surveillance efforts.
The approach, the experts told STAT, is likely resulting in both an underestimate in the total number of cases and flawed assumptions about fatality rates calculated by those who ignore the repeated caution that it’s too soon to do that math.
The experts were quick to note that the Chinese are not willfully underreporting cases. Rather, the approach is a testament to how challenging data collection can be during the early days of an epidemic. When thousands of sick people show up at hospitals looking for care, there is no time to go searching for people who have mild symptoms and who have stayed home.
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“I think right now things are so chaotic in China it may be hard to collect data on the whole spectrum of illness,” said Michael Osterholm, director of the Center for Infectious Diseases Research and Policy at the University of Minnesota.
Officially, an estimated 20% of cases in China are severely ill, according to the World Health Organization. But that calculation is derived based on known cases, and would not reflect mild, undetected ones.
Without knowing for sure what percentage of cases is severe — and how easily the pathogen that causes the disease can be transmitted — it’s impossible to forecast what might happen if the virus continues to spread globally, the WHO’s emergencies chief, Mike Ryan, told reporters Wednesday.
“We don’t understand either of those parameters well enough to make accurate predictions,” he said. Still, he added a warning for people who are concluding that the virus may be less fatal than some other known pathogens: “A relatively mild virus can cause a lot of damage if a lot of people get it.”
The outbreak has infected upward of 7,700 people on the Chinese mainland, and killed 170 since the new virus, known provisionally as 2019-nCoV, was reported to the WHO on Dec. 31. Nearly 20 other countries have reported diagnosing infections in travelers from the Chinese city of Wuhan, the epicenter of the outbreak, but to date there has been little local spread of the virus in other countries.
WHO Director-General Tedros Adhanom Ghebreyesus and Ryan, who were in China earlier this week to consult with the Chinese government and assess the situation, praised the response by officials there. “The challenge is great but the response has been massive,” Ryan told reporters.
The effort, which is of an unprecedented scale, involves quarantining whole cities that are home to tens of millions of people to try to stop spread of the virus. The WHO is still hopeful, Ryan said, that China will be able to stop the outbreak.
If it cannot — or if exported infections seed outbreaks in other parts of the globe — the world could be looking at a more disseminated epidemic, admitted Tedros, as he is called.
Among other factors, epidemiologists are interested in the severity of the outbreak and what is known as the virus’ “attack rate.” The attack rate means the percentage of people who will develop the disease if it spreads.
With seasonal influenza, the Centers for Disease Control and Prevention estimates between 3% and 11% of people become sick with flu every year. But immune systems have experience with influenza; the attack rate might be higher with a virus that is wholly new to humans.
Likewise it’s unclear how many mild infections are being missed. The Chinese are currently only testing people who are sick enough to seek medical care because they have pneumonia — a criterion that automatically excludes anyone on the mild end of the disease spectrum.
With some diseases, there isn’t much mild illness. In the case of the 2002-2003 SARS outbreak, for example, most people who became infected ended up in hospital, noted Dr. Gabriel Leung, dean of medicine at Hong Kong University and a veteran of that city’s battle against the disease.
It’s clear there are at least some mild cases with this new infection. Many of the 100 or so exported cases are people with mild illness; to date there have been no deaths among these cases. Some of the five cases in the United States are only in hospital to ensure they don’t infect anyone else. Such cases would not be tested in China using the current case definition.
“The look and feel of the exported cases, I think, really support the argument that there’s a lot of mild disease that is not being detected in China at the moment for the very good reason that they just can’t do it,” said Dr. Allison McGeer, who fought SARS in Toronto and helped contain hospital outbreaks of MERS in Saudi Arabia. Both SARS and MERS are coronaviruses, related to the new virus.
McGeer, an infectious diseases researcher at Toronto’s Mount Sinai Hospital, noted the types of studies needed to estimate how much mild disease this virus causes are very difficult to do.
Infectious diseases experts use the analogy of an iceberg when they talk about the spectrum of a disease. The most severe cases represent the tip of the iceberg; they are visible, because they are sick enough that they seek health care.
But the portion of the iceberg that is under water is harder to calculate, especially with a new disease. And without having a clear picture of total cases, it’s difficult to come up with an accurate fatality rate.
Wang Linfa, director of the program in emerging infectious diseases at Duke-NUS Medical School in Singapore, is convinced there are a lot of mild infections. “Mild cases don’t go to hospital and there’s many, many cases that remain to be confirmed,” he said, noting laboratories are struggling to keep up with testing amid a reported shortage of test kits.
Leung agreed: “It looks like the submerged bit of the iceberg is fairly large for this thing.”
Some of the answers China cannot currently generate will come from watching what happens with the exported cases, said Dr. David Heymann, who oversaw the WHO’s SARS response and now teaches at the London School of Hygiene and Tropical Medicine. “Now we are really going to begin to see things,” he said.
Countries outside of China are using a broader approach to testing, looking for anyone who has recently traveled to or from Wuhan who has respiratory symptoms. These people, who the CDC calls “persons under investigation” or PUIs, do not need to have pneumonia in order to be tested.

I don’t like the contrast of Facebook and social media where it was dipicted that the coronavirus was alot worse than what the media had us believe with a Wuhan nurse rumoured to have said in a voice recording that 100 thousand people had it. Then there were sstories of China hiding true death toll by cremating bodies. Then media explaining this type of civilian public feedback are hoaxes! I don’t believe them.
Ask yourselves, why would all these hoaxes come out so soon after announcement? What would be the purpose of that? There must be some truth to it.
I don’t believe only 304 people dead, there must be far more dead than that (and they know it) as why would China rush to build a hospital in ten days and introduce the military? And taking other extreme affects such as talks of investing a trillion into their market, you don’t do drastic things like that if only 304 people are dead. The number must be alot higher as the big actions speak for themselves. China and the MEDIA you are big FAT LIARS.
This is what I predict too with a lower bound of confidence interval of deaths to be 25% with 25 days lag if I consider the numbers from the New England study.
With the confirmed cases that are posted officially, the picture is gloomier as you describe. This is really worrying.
There are some questions that cannot find any specific answers. For example how many tests can the CDC, or any institute complete per day?
Is the rate we see now, the rate of the virus in the early stages or the ceiling of the number of tests that can confirm the cases?
What is the proportion of positive/negative results per day, especially in countries in early stages?
It is published elsewhere that the disease takes on average 10 days to show symptoms and in severe cases an average of 11 days for elderly to die and 15-40 days for younger people to die.
If this is the case, should we find the death rate by the proportions of the deaths today by at least the confirmed cases 25 days ago? If this is the case, then the death rate is 25% that is extremely high.
Also the New England study refers to 425 confirmed cases in the middle of December, how does this compare with 224 confirmed cases on 1/21, that are reported?
People are worried and based on what I understand they should be worried, balancing the information we share and the panic we create is important but at this point, it is important to hear the truth, as we depend on everyone being extra careful, so we can be healthy.
I have previously posted on rate of deaths with reference to the issue of lag – between diagnosis and death and the resultant massive under-estimate of the death rate at 2%. Based on the latest figures, the increase in the number of deaths has averaged more than 25% (actually 27%) PER DAY over the past week, which equates to a 5-fold increase in a week. Expect death number to be around 1500 by next Saturday. Around double the deaths from SARS. Nothing to worry about!
While observing brief .i came upon one of the comments .that which poses the question as to why did it takes so long for China to be aware of this form of a crisis as there were indications that this was mostly likely to take place or happen . well while i am unable to state exactly as the reason or reasons . There are multiples of reasons that one could interpret .base on the culture and state of this most populous Nation Globally with an estimate population of one point four Billion Human Beings . secondly the Communists structure there off along with the Leadership did not wish nor intend to give any form of information to the public globally with the fear that this would affect this nation extensively and tragically . just as how it is currently . Secondly The Main Stream Media Of The Fourth Estate deliberately denied or hold this crisis along with others such ones as they were and still are only interested .devoted . in love with and hold one issue dearly to The Hearts Of Them . so that they would hold on to their Love Of Power , Rather Than The Power Of Love .The Issue And Or Subject that I am referring to or with is none other than Climate Change Or Global Warning . Their ?s Love Affairs with this is one Reason as to why they came up with two [2] names . Yes . More than Forty Percent of The Nation Of China ?s Pork Industry were destroyed . eliminated and or taken away by The Antimicrobial Resistant Super Bugs in about Seven or Nine Months ago . forty percent of China?s Pig Industry is about Seventy to Eight Million Pigs . as China is the largest Pig industry as Pork is the biggest meat that the people consume .plus the nation also export a portion of . Yes with all of The above A Significant percent Of The Global Population was unaware of This Crisis and others . simply due to The lack of information and news report by The Main Stream Media Of The Fourth Estate . again their only interest and love affair were and still are Climate Change for which they talk about Millions upon Millions of Time That This is the only thing that is going to destroy the world in Less Than Ten Years . Do i say more ? thank you all Trevor .Merchant . Bronx .New York City . at 2.11 p.m . eastern standard time . 02. 01.2020.
No problem with cutting funding for the CDC, alienating China with a phony trade war, and using a public health crisis for marketing. It is kind of late, since the cat is out of the bag. One would think this would cause a serious look at global disease response, and failures in the American healthcare system. We are already seeing so much misinformation, and marketing. They are hawking stocks, that might go up in response to a global pandemic. Our corrupt and broken for profit healthcare system is not equipped to handle any kind of public health issue.
Thing is, its the ones that left China to share it with the rest of the world.
5 million left prior to lockdown, Wuhan mayor apologizes.
https://www.foxnews.com/health/wuhan-coronavirus-criticism-mayor-offer-resignation-as-apology
https://www.telegraph.co.uk/news/2020/01/27/chinese-premier-li-keqiang-wuhan-lead-emergency-efforts-coronavirus/
How long did China wait to announce this New Virus , when were they alerted after 100 people were infected or 500 people ?? Why did it take this long and why was it not talked about Sooner ..
Actually the people in Wuhan didn’t even realize the grave situation of the virus the day before the city was locked down. The mayer of city told the reporter that he had reported to his senior but he was not allowed to disclose to the public until Beijing permits. If you had any fantasy of the Chinese model, please don’t. The government’s first priority is to stablize their grip of power. The lives of the citizens are in their lowest priority. HK can’t shut down its border even now. Even though 90% of the citizens are begging the government, HK gov refuses to act because it does not have permission from Beijing. People in HK are doomed.
If the Chinese can’t include the mild cases, then that would bring the fatality rate down even more. The concern is them underreporting deaths. But again, we just don’t have all the numbers. From what I’ve seen so far, it appears that the vast majority of cases are mild; however, for the elderly or sick already, it could be devastating, esp if you need ventilation. The problem is it doesn’t take much to overwhelm a facility. What happened in China was it was mismanaged from the start, and no one knew this highly contagious disease was spreading. Before they could clamp down and warn everyone, it had hit critical mass and took off. And literally took off because Wuhan residents fled before the lock down. Now that the world is watching, I suspect that while we might see located spreads, there shouldn’t be this enormous explosion of cases that occurred in China. However, that’s not to say there won’t be. It is just to say that people have now been warned and are taking more precautions. The Wuhan virus is as easy to catch as a cold, but as potentially unpleasant and deadly as the flu. Due to the ease at which in can be transmitted and the severe respiratory problems it can cause, even in a minority of cases, it can quickly overwhelm medical facilities. That’s what we are seeing now. The medical systems are their breaking point. And that could happen anywhere and of course, it isn’t pretty when it does. That’s why it needs to be taken seriously, so we can treat the ones we can, not overwhelmed our hospitals, and let the vast majority get well on their own without any medical treatment at all. Everyone has said this illness is not as deadly as SARS, unless, of course, you are elderly or have a weakened immune system and/or there is no hospital to provide respiratory support.
I cannot believe that the Chinese Officials were not aware sooner and now people are mocking it already .. This is a simplistic way of saying nothing .. The Global Community is not Honest about these diseases until it becomes the Overwhelming issues .. The News won’t report anything but how we don’t have to worry ??
I am not buying this ,