Since 31st December 2019 there has been an outbreak of a new coronavirus in China. It originated in the city of Wuhan, and over the past 22 days has spread rapidly, including cases in several cities outside China. Initial reports suggested it originated in a seafood market in the city, which had me hoping it was the world’s first fish-to-human infectious disease, though I think we need to wait a while before we establish exactly where it started. It appears to have achieved human-to-human transmission, which is unusual for these zoonotic (animal-origin) viruses. International media are of course reporting breathlessly on it, and you can almost feel them salivating over the possibility of another SARS-style catastrophe. But how dangerous is it?

In this blog post I would like to use some initial data and reports to make an estimate of how dangerous this disease is, for those who might be considering traveling to (or canceling travel to) China. I’d also like to make a few comments on the reporting and politics of this disease, and infectious diseases generally.

The Case Fatality Ratio

For the sake of easy writing, let’s call this new disease Dolphin Flu, since it originated in a fish market. The main measure of how deadly any infectious disease is is its case fatality ratio (CFR), which is the number of people who die divided by the number of people infected, multiplied by 100. It seems to be a natural law of infectious diseases that the more infectious a disease is the less fatal it is, and anyone who has played that excellent pandemic game on their phone will know that there is a cost associated with a disease being infectious, which is usually that – like the common cold – it spreads fast but kills no one. Understanding the CFR is important to understanding how nasty a disease is likely to be. Here are some benchmark CFRs:

  • Untreated HIV: 100% (i.e. 100% of people infected with HIV die if they aren’t treated)
  • Untreated Ebola: 80-90%
  • Malaria (Africa): 0.45%
  • Spanish influenza (1918): ~3%
  • Measles: 0.2%

Nature is pretty, isn’t she? It’s worth noting that Spanish Influenza was a global catastrophe, which had major political and economic consequences, so any disease with a CFR around the level of influenza that is similarly infectious is a very scary deal. Ebola and HIV are extremely deadly but also not very infectious (you have to have sex to get HIV, which means my reader(s) face almost zero risk). It’s the respiratory diseases (the lungers) that really worry us.

Calculating the Case Fatality Ratio for Dolphin Flu

In order to calculate the CFR we need to know how many people are infected, and how many have died. Official government data this morning (reported here) puts the death toll at 17 people, and we can be fairly sure that’s correct, so next we need to calculate the number infected. This excellent website tells us there are 555 confirmed cases, but this is not the right number to use for this calculation, because with all of these respiratory-type diseases there are many cases who never go to a doctor and/or never get confirmed. In ‘flu season we call these “influenza-like illnesses” (ILI) and they are important to understanding how dangerous the disease actually is. In fact for many of these diseases there is an asymptomatic manifestation, in which people get the disease and never really show any symptoms. So we need to have an estimate of the total number of cases including those that were not confirmed. Fortunately the excellent infectious disease team (who do a great course in infectious disease modeling if you have the money) at Imperial College have used the number of cases appearing at non-Chinese cities to estimate the total number of cases using data about travel flows from Wuhan city. Their headline estimate at this time is 4000 cases, with an uncertainty interval from 1000 to 9700.

Next we need some information on other diseases. The CDC website for seasonal flu tells us that in the 2017-2018 season in the USA there were 20,731,323 confirmed cases of influenza, 44,802,629 total cases (including unconfirmed) and 61,099 deaths. A Japanese research paper on the H1N1 pandemic tells me there were 637,598 total cases (including unconfirmed) and 85 deaths due to H1N1. The Wikipedia entry on H5N1 bird flu tells me there were 701 confirmed cases and 407 deaths (I think there were very few unconfirmed cases of bird flu because it was so nasty).

Putting this together, we can get the CFR for confirmed and unconfirmed Dolphin Flu, and compare it with these diseases, shown below.

  • Unconfirmed Dolphin Flu: 0.43%, ranging from 0.22% to 1.7%
  • Confirmed Dolphin Flu: 2.98%
  • Unconfirmed Seasonal Flu (2017-18 season, USA): 0.14%, ranging from 0.11% to 0.16%
  • Confirmed Seasonal Flu (2017-18 season, USA): 0.29%
  • Unconfirmed H1N1 (Japan): 0.01%
  • Confirmed H5N1 (Global): 58.06%

This suggests that Dolphin Flu is between 2 and 10 times as dangerous as seasonal influenza, and about as dangerous as malaria if you are infected with malaria in an African context (i.e you may not be able to afford and access treatment, and you’re so used to idiopathic fevers that you don’t bother going to the doctor until the encephalitis starts).

That may not sound dangerous but it’s worth noting that seasonal influenza is one of the most dangerous things that can happen to an adult of child-bearing age except getting in a car and childbirth. It’s also worth noting that depending on the degree to which the Imperial College team have overestimated the number of unconfirmed cases, Dolphin Flu could be heading towards half as dangerous as Spanish Influenza. We don’t yet know if it is as contagious as influenza, but if it is …

I would say at this stage that Dolphin Flu looks pretty nasty. I probably wouldn’t cancel travel, because it’s still in its early stages and the chance of actually getting it is tiny (especially if you aren’t in Wuhan). But tomorrow is Chinese New Year, the largest movement of people on the planet, so in a week I expect that it will be all over China and it may be much harder to go there without getting it. I guess in that context the decision to quarantine Wuhan makes sense – if it’s half as dangerous as Spanish Flu, it’s worth suffering the short term economic damage of shutting down one of China’s largest cities to avoid spreading a disease that could be a global catastrophe.

So, given that information, would you travel? And what decision would you make if you were an administrator of public health in China?

About Cover Ups and Authoritarianism

Media coverage of disease outbreaks almost invariably follows western stereotypes about the country where they happen. With Ebola it’s all about bushmeat-eating primitives who can’t understand modern medicine; with MERS it was secretive religious lunatics; and with anything coming from China it’s a weird mix of Sinophobia, orientalism and obsessions with China’s authoritarian government. Because China fucked up the SARS response, we can see Western media basically salivating at the chance to report on how they’re covering this up too. But it’s important to understand that unconfirmed cases are not covered up cases. With respiratory diseases there will always be unconfirmed cases and there will always be someone who slips through the net and goes traveling, spreading the disease to other cities. Indeed, with a completely new disease it’s entirely possible that there are asymptomatic cases that no health system can detect.

In fact this time around the Chinese response has been very quick, open and transparent. They notified the disease to the WHO on 31st December, probably very soon after the first cases appeared, and the WHO Director-General has been fulsome in his praise of the Chinese response. Within perhaps 10 days of notifying the disease to the WHO they had isolated the virus and developed tests, and now they have quarantined a city of 12 million people because they know that the impending Chinese New Year could cause major transmission risks. Before complete quarantine they had introduced fever checks at exit points to international destinations, another sign of taking the disease seriously. This is unlikely to be successful if the disease has an asymptomatic phase (since you get on the plane before you have a fever) but short of blood-testing everyone in the city, there is little more that anyone could expect the government to do.

How to handle western media panic

None of this will stop western media from playing to the west’s current fear of China, and once the disease is over you can bet they will start talking about how the Chinese response was too authoritarian. You can also bet that the mistakes the administration inevitably makes will be discussed as if they are hallmarks of a Chinese problem, rather than mistakes any government could be expected to make when trying to control a disease that spreads at the speed of a cough. And this will all be made worse by the way western media get into an absolute lather about infectious disease stories. So be cautious about stories about China’s cover-ups, about authoritarianism, and avoid believing disease panics. Check in with the WHO’s updates, read the Imperial College website, and be careful about the western media’s over-hyping of disease threats and Chinese collapse. For a balanced view of infectious disease issues generally (and excellent coverage of the tragic, ongoing Ebola Virus outbreak in DRC) I recommend the H5N1 blog. For understanding how to interpret risk, I recommend reading David Spiegelhalter’s twitter. And remember, when you’re balancing risks, that getting in a car, or choosing to have a child (if you’re a woman) are probably the two most dangerous things anyone in a developed nation can do in their lives. You don’t need to go to China to experience any of those risks!

Let’s hope that this disease turns out to be another fizzer, keep a level head, and don’t let western media hype scare us!

About the picture: The picture is from the Twitter thread of @CarlZha, an excellent independent Chinese voice. It’s a photo of some guys doing renovation work on a clinic somewhere in China. There isn’t actually a Zombie outbreak yet!