* Jack: not his real name. The account of Jack’s travels, including his companions, travel destinations and other details have been modified, but broadly represent the real-life scenario.
This is a fictionalised case study designed to highlight the principles of epidemiological reasoning.

It is NOT advice on whether to travel to China. We have based this case study on publicly available information about Wuhan Coronavirus emergence and spread at the time of writing, but it is very early stages in this outbreak, not all relevant information may yet be available, and the situation is likely to change rapidly over the coming days and weeks.

What is the Wuhan Coronavirus and where did it come from?

An unusual outbreak of pneumonia was first detected amongst patients in a hospital in Wuhan, a city of 11 million people in Hubei province in China in December 2019. Tests revealed this cluster was caused by a coronavirus previously unknown to scientists.

The new coronavirus has emerged from an animal origin, but it is unclear which species at this stage. Coronaviruses originating in bats were responsible for both Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS). In both cases, bat coronaviruses spread to other animals (known as ‘intermediate hosts’) – civets in the case of SARS, and camels for MERS, which may have been the source for the first human cases.

The first four cases of Wuhan Coronavirus were identified in people who worked at Huanan Seafood Wholesale Market in Wuhan. “Wet markets” are a common source of meat and fresh produce in Chinese cities, and many wet markets sell live animals. Animal species sold at Huanan Seafood Wholesale Market reportedly included poultry, snakes, giant salamanders, crocodiles, rats, marmots, porcupines, hedgehogs, otters, civets, dogs, foxes, wolf pups, deer and camel meat – but not, despite some media reports, koalas.

As of 20th January, Wuhan banned trade of live animals at food markets in response to this outbreak.

About Jack

Jack is a 57-year-old man living in Australia, who has booked a family holiday to China in 2 weeks’ time. Jack will travel with his wife Jill (54 years old), and their daughter Emily (34 years old) and her family, which includes her husband Mark (38 years old), and their children, Phoenix (6 years old) and Hunter (3 years old).

Jack has Type 2 diabetes, but it is well managed with medication. Jill had severe asthma as a child, and still has occasional flare-ups. She was originally concerned about being exposed to air pollution, but is now particularly concerned about contracting this new coronavirus as she’s heard it’s causing severe pneumonia.
Emily is pregnant with their third child, and she, Mark and their children are in good health.

Are Jack and his family at risk by travelling to China?

As there are no confirmed cases yet in Australia, we assume that Jack and his family are not at risk unless they travel to China.

Of course, this may change, as many countries outside of China have already confirmed cases, and there is potential for further spread. The risk of spread depends on the frequency and volume of international air travel, as well as biosecurity measures that are in place in the country of origin and country of destination. Researchers from James Cook University have made an interactive pandemic model publicly available that estimates risk of disease spread using international travel data (air travel and land crossings). Have a play with it here. By inputting some of the basic information known about the outbreak to date, such as the current number of cases, a preliminary R0 of 1.4 – 2.5, the current case fatality rate of 3-4% and a guess that the infectious period might be up to 20 days, the model suggests that Wuhan Coronavirus will first spread further in Asia, but is unlikely to lead to more than a handful of cases in Australia even in the absence of quarantine and other control measures. Basically – this virus does not seem to be easily transmitted between people, though if the virus mutates further, that may change.

But this information only helps us to know about international disease spread. We also need to consider disease spread within China.

Jack and his family are planning to fly into Guangzhou, and then visit Chengdu (to see the pandas), Chongqing (for a Three Gorges Dam cruise), Beijing and Shanghai, before flying home. They’re not going to Wuhan, the epicentre of the outbreak, but cases have been reported in all of the cities they are planning to visit.

Most of these cases are thought to have occurred in people who live in or have travelled to Wuhan Province, however as many as 50% of cases may have had no links to the wet market at the centre of the outbreak, or had contact with known cases.

Jack and his family’s travel itinerary in China, starting in Guangzhou and flying out of Shanghai.

To reduce the risk of the outbreak spreading further, China has imposed travel restrictions on people currently in Wuhan and neighbouring cities. However, an estimated 300,000 people may have left Wuhan via train in the 24 hours before restrictions were imposed, based on average passenger train travel statistics for the region.

This means Jack and his family could be at risk even if they don’t visit Wuhan.

Who in Jack’s family is most likely to get sick?

The median age of confirmed cases in China is 57 years old, the same age as Jack. Most deaths have occurred in older people. So far, younger people have been much less affected.

But why is it the case that older people are most at risk?

An obvious part of the explanation is that older people are more likely to have pre-existing conditions and overall poorer health status that weakens their immune system capacity to fight the infection. Older people are also more at risk of severe illness and death due to seasonal influenza for this reason.

What about Emily and her family? Pregnant women were particularly at risk during the swine flu (H1N1) epidemic in 2009, are they at risk from this new coronavirus?

To understand the population at risk, we need to understand not only who is getting sick, but also who is getting exposed to the virus. Wet markets in China are more frequently attended by older people in the first place – this may because they have more time to go shopping at wet markets during the day when younger people are at work, there may be generational preferences for wet markets versus supermarkets, and the population who works at wet markets may be older on average. These factors influenced the most recent bird flu outbreak in China (H7N9). Older men were the most affected population group, but it was found that in addition to having more health issues, they were also more likely to visit or work in wet markets.

So, it’s hard to say at this stage if the coronavirus will affect pregnant women, children and other vulnerable populations in younger age groups more severely, as many may not have yet been exposed.

What can people do to protect themselves?

Basic hygiene measures such as handwashing are critically important for preventing spread for a wide range of infectious diseases. As the coronavirus appears to be transmitted by direct contact or via respiratory secretions, handwashing remains an important practice.

What about facemasks? There have been mixed messages about the effectiveness of different types of facemasks for preventing respiratory diseases. A study last year found that when worn properly, standard surgical facemasks (similar to what you see many people wearing in public) are just as effective at preventing influenza infections in healthcare workers compared to more expensive N95 respirators.

However – facemasks are only effective if you actually wear them. In a recent study, less than half of people provided with facemasks to prevent influenza at home, work and other locations wore them most of the time, and they were no better protected against influenza than people who never wore facemasks.

Another study suggests that facemasks might be most effective at preventing a sick person from spreading the disease, rather than preventing a healthy person from being infected.

What are the unknowns?

In many outbreaks, the investigation doesn’t even start until it’s (nearly) over. China has been moving remarkably fast to understand and contain this outbreak, but at this early stage, there are still a lot of unknowns.

The source of the outbreak has not been completely identified, and there may still be infectious animals in circulation through other markets. An open question is where the animals at the Wuhan wet market came from. Live animals and meat are transported from across China through complex market chains, with intensively raised poultry and seafood arriving alongside live wild animals purchased from hunters or illicit breeders. It’s possible that the original viral spillover event (when the virus ‘jumps’ from one species to another) took place at a farm outside of Wuhan, which may be continuing to supply other wet markets. If this is the case, there is a risk of another outbreak starting elsewhere in China.

Alternatively, the spillover event may have taken place inside the market itself. Since the H7N9 epidemic, there have been restrictions in place on the length of time live poultry can be kept at wet markets – but this is not necessarily the case for other live animals. Caged animals of different species may be kept in close proximity for several days or longer until they are sold – and this substantially increases the risk of a virus passing from one species to another, possibly ‘amplifying’ in intermediate hosts before transmitting to people. The China Center for Disease Control reported that 15 environmental samples from Huanan Seafood Wholesale Market tested positive for the new coronavirus, but could not yet be definitely linked to an animal source. In this case, reducing travel from Wuhan, and banning live animals at Wuhan wet markets, could slow disease spread substantially.

We don’t know much about which population groups are most at risk of getting exposed, how easily the virus is spreading between people, or how many people are getting sick. If you recall – an early investigation found that many of the confirmed cases had not had contact with the Wuhan wet market, or people with symptoms of respiratory disease. This means that either – people are infectious before they have symptoms, or people with mild or asymptomatic infections can transmit the virus. If the former, this makes it much more challenging to detect infected people through measures such as fever screening (in contrast, during SARS, most people had symptoms before they could spread the virus). If the latter, it suggests that the spectrum of clinical disease is wide, and that many more people are likely infected than currently reported, because they are not sick enough to seek health care and therefore be diagnosed. This may mean that this virus is likely to spread easily, as these people will not be quarantined. In general, diseases that spread easily tend to make fewer people sick (‘low virulence’).

What should Jack do?

At this stage, the best advice is to monitor the situation. It’s likely to keep changing rapidly in the next two weeks. Jack should keep an eye on WHO advice and government travel advisories, and he and his family should seek medical advice about their specific risks.

One thing Jack shouldn’t do is panic. As ever, there’s a lot of hysteria in the media about this outbreak. Tabloids are screaming fears about a “killer virus” on their front pages. Keep in mind that firstly, the current death rate in confirmed cases in China is around 3-4%, and this is similar to seasonal influenza. Secondly, it’s very likely that many people with mild or asymptomatic infections are not coming to the attention of the health authorities, because they’re not sick enough to seek health care. This means the true death rate is likely to be much lower.

The chance of being exposed to Wuhan Coronavirus in China is relatively low due to the very high human population in China. However, the greatest risks of exposure are in places where people congregate, such as during travel by air, rail and bus, and in produce markets.

Finally – we should all keep in mind that this new coronavirus is yet another stark reminder that the majority of new human infectious diseases originate in animals, especially in relation to food production. One Health approaches remain crucial for prevention, early detection and response to new infectious diseases.