Skip to Main Content

One of the hopes of people watching China’s coronavirus outbreak was that the alarming picture of its lethality is probably exaggerated because a lot of mild cases are likely being missed.

But on Tuesday, a World Health Organization expert suggested that does not appear to be the case. Bruce Aylward, who led an international mission to China to learn about the virus and China’s response, said the specialists did not see evidence that a large number of mild cases of the novel disease called Covid-19 are evading detection.

“So I know everybody’s been out there saying, ‘Whoa, this thing is spreading everywhere and we just can’t see it, tip of the iceberg.’ But the data that we do have don’t support that,” Aylward said during a briefing for journalists at WHO’s Geneva headquarters.

advertisement

Getting a handle on how many people have actually been infected is crucial to assessing how dangerous this virus is. During the early days of an explosive outbreak with a new pathogen, it is hugely challenging to look beyond the people streaming into hospitals for care to see whether there are many more at home with a mild cold or manageable flu-like illness.

If large numbers of mild or virtually symptom-free cases are evading detection, that would suggest that estimates of the proportion of people who might end up in ICUs or might die during a Covid-19 epidemic would be lower than what has been seen to date in China.

advertisement

But if there aren’t large numbers of uncounted cases, the severity seen in China is what the rest of the world should expect as the virus moves to new locations, especially if it spreads to the degree seen in Hubei province, where the outbreak began.

“What [the data] support is that sure, there may be a few asymptomatic cases … but there’s probably not huge transmission beyond what you can actually see clinically,” Aylward said.

The claim was quickly challenged by an infectious diseases expert who serves on a committee that advises the WHO’s health emergencies program.

Coronavirus Coverage: Read the rest of STAT’s up-to-the-minute reporting on the coronavirus outbreak.

Gary Kobinger, director of the Infectious Disease Research Center at Laval University in Quebec, said it would be highly unusual for there not to be mild or symptom-free cases that are being missed. He pointed to the fact that outbreaks have popped up in countries far from China — including Iran and Italy — because people with mild infections were not detected and traveled to other places.

“There are mild cases that are undetected. This is why it’s spreading. Otherwise it would not be spreading because we would know where those cases are and they would be contained and that would be the end of it,” said Kobinger, who insisted that mild, undetected infections cannot be ruled out until people who haven’t been diagnosed with the illness can be tested for antibodies to the virus.

Those kinds of tests, called serology tests, are just becoming available in China, Aylward said.

“As long as we do not have good serology data, I think that it is completely speculative to say that there are no undetected cases,” Kobinger said.

Aylward pointed to an analysis from Guangdong province suggesting that, at least there, most of the infections were coming to the attention of health authorities.

When the virus started to spread in Guangdong — the province where the 2002-2003 SARS outbreak began — worried people flooded fever clinics to be tested. Of 320,000 tests performed, just under 0.5% were positive for the virus at the peak of transmission there, he said — which suggests that only 1 case out of 200 was being missed.

Transmission of the virus has subsided in Guangdong, and the number of positive tests at the fever clinics has declined; now only about 1 in 5,000 people tested at the fever clinics is positive for the virus, he said.

Aylward said that across China, about 80% of cases are mild, about 14% are severe, and about 6% become critically ill. The case fatality rate — the percentage of known infected people who die — is between 2% and 4% in Hubei province, and 0.7% in other parts of China, he said.

The lower rate outside of Hubei is likely due to the draconian social distancing measures China has put in place to try to slow spread of the virus. Other parts of China have not had the huge explosion of cases seen in Hubei, Aylward said.

A case fatality rate of between 2% to 4% would be catastrophic, if the virus spreads widely and infects a lot of people. Even a case fatality rate of 0.7% — which means 7 out of every 1,000 infected people would die — is sobering. It is seven times the fatality rate for seasonal flu, which is estimated to kill between 290,000 and 650,000 people a year globally.

An earlier version of this article included a reference to the case fatality rate of the 1918 pandemic that is contested in some quarters.

  • You wrote “A case fatality rate of between 2% to 4% rivals and even exceeds that of the 1918 Spanish Flu pandemic, which is estimated to have killed upwards of 50 million people.” That’s not true. The Spanish Flu killed around 3% of *the entire world population* at the time. That’s much higher than the fatality rates we’re seeing for COVID 19 for *the specific group of people who have contracted the disease*. COVID 19 has a higher fatality rate than the ordinary flu but definitely lower than the Spanish flu. The Spanish flu killed 10-20% of the people who contracted it.

  • We need to tell people that they must be prepared for this is the only way to survive a pandemic. People need to know, that they may get sick, and their sickness is not that bad and they most likely would not die if they treated their fever and hydrated themselves. However, a person may die if they cannot get a fever reducer. You not only can die to form the virus, but you can also die from not having simple meds to help you recover. Also, the USA government is saying have two weeks’ worth of food. Let me say it like this, you better have more than two weeks of food. Truck drivers will be sick, store employees will be sick and the warehouse people will be sick, with all this it means there will be shortages of food. We just do not know.

  • What kind of test is used to determine whether you have the virus. Is that a serology test, too? Could a person give the test to themselves, in their home (if it were delivered) and determine the results themselves? That would prevent people from going to a dr. or hospital and infecting others unnecessarily.

  • A couple of problems. As other comments note, this statement is wrong in terms of basic math:
    “When the virus started to spread in Guangdong — the province where the 2002-2003 SARS outbreak began — worried people flooded fever clinics to be tested. Of 320,000 tests performed, just under 0.5% were positive for the virus at the peak of transmission there, he said — which suggests that only 1 case out of 200 was being missed.”
    This describes the percentage of the population infected, but says nothing about the proportion of people who are asymptomatic — that would require a comparison with the number of people from the same population who were infected.

    This excerpt also makes no sense:
    “The lower rate outside of Hubei is likely due to the draconian social distancing measures China has put in place to try to slow spread of the virus. Other parts of China have not had the huge explosion of cases seen in Hubei, Aylward said.”
    The social distancing measures would impact the spread of the disease, but not the outcomes once people were infected. The high mortality rate in Hubei probably speaks more to poor conditions at hospitals where sick patients were being treated. If that is true, the 0.7% in other areas of China (sometimes reported as 0.4%, as compared to about 0.1% for the seasonal flu) is probably more in line with what we should expect in countries with the resources to handle an outbreak. Areas with fewer capabilities to respond the epidemic would have higher mortality rates. Of course all of this comes with caveats that we don’t have good enough data or understanding of the biology of this virus to make definitive statements.

    This is a serious issue, so please get your facts and basic reasoning straight. As it is, it is impossible to interpret whether this is a serious issue being mis-reported, or a flawed piece exaggerating the dangers of the epidemic.

  • I have an observation to make. Let me write it as a question.

    Why are there no cases reported of transmission by cargo from infected people?

    That can explain the mystery infections occurring around the world.

    Example – a factory in China packages some computers or computer parts and exports them to California in the USA. Someone unpacks them and gets infected hands and then it goes to the nose and the body. This person is then a spreader and someone is found to test positive without having any personal contact with any chinese or other travellers from infected areas.

    My next question is this:
    Reportedly California has only 200 test kits available. What are the implications of that,

    My third observation is this: Once the hospitals are full critically ill patients will die in greater numbers. They are not being treated.

    Fourthly. How many people will become infected world wide seems to me to be something that cannot be estimated. We may or may not have a vaccine before everyone is infected. And why would some people never be infected?

    • Relax. All viruses will lose their ability to invade human and animals, or basically, be dead in a few minutes after leaving their living medium, which usually is animal body fluid or animal cells. No virus can survive at a metal surface for more than 1 hour if the metal surface is not moisturized and if its temperature is far from human body temperature.

  • Regarding: ” just under 0.5% were positive for the virus at the peak of transmission there, he said — which suggests that only 1 case out of 200 was being missed.”

    That is not how it works. You need to divide the number of “missed cases” by the sum of the “missed cases” and the “tested positive cases” to get the “miss %”. What you are describing is essentially the % of the population that is infected.

Comments are closed.