Novel coronavirus and border screening – Expert Reaction

Kiwis currently in Wuhan will be evacuated in a joint Australian-New Zealand operation, as a novel strain of coronavirus continues to spread from the area.

In the latest update from the World Health Organization (WHO), there have been over 6,000 confirmed cases of the novel coronavirus worldwide, with 68 cases outside of China. There have been 132 reported deaths within China.

The WHO will reconvene its Emergency Committee on Thursday in Geneva to advise whether the outbreak constitutes a Public Health Emergency of International Concern.

The SMC gathered expert comment on the coronavirus.

Professor David Murdoch, Dean and Head of Campus, University of Otago, Christchurch, comments:

“There are still many gaps in our knowledge about this novel coronavirus and, like everywhere else in the world, we are learning more each day about the virus and the infection it causes. Although there is still a lot we don’t know about the virus, the broad context of this outbreak is one with which we have some familiarity. Existing knowledge about similar viruses and their behaviour help us a lot.

“Respiratory viruses typically cause illnesses ranging from the common cold at the milder end of the spectrum through to infection of the lung tissue itself (pneumonia), which can be life-threatening. We are still working out where the novel coronavirus fits on this spectrum. Some coronaviruses that we encounter every year rarely cause anything more than the common cold, while SARS and MERS coronaviruses were responsible for outbreaks that caused pneumonia in a relatively high proportion of cases.

“An early report from China on 41 people admitted to hospital with novel coronavirus infection indicated that all had pneumonia and one third had other underlying medical problems. However, it is important to note that this report only includes cases who were unwell enough to be admitted to hospital. It is also important to bear in mind that we tend to hear more about the most severe cases in the early stages of a new disease, as these are the cases first brought to our attention. We still do not know the full spectrum of disease, including what proportion of those infected have mild or no symptoms at all. The proportion of cases who die is one marker of disease severity, and the information we have to date indicates that the known case fatality associated with infection with the novel coronavirus (~2% with current data) is less than with the SARS epidemic in 2002-2003. We still do not know why some people die from this new infection and some people do not. In general, those with more severe disease caused by respiratory viruses tend to be people with underlying medical problems and/or with impaired immune systems.

“Other critical information that helps develop prevention and control plans include an understanding of how easily the virus is transmitted between humans, the duration of transmission in humans, the mode of transmission, and potential sources of infection. Early information is that between 1.5 and 3.5 people will be typically infected by each case – similar to influenza, but much less than measles. There have also been reports of potential transmission while a case was without symptoms, but this has yet to be substantiated. Based on our understanding of the evolution and natural history of other respiratory viruses, including SARS and MERS, there is every expectation of non-human animal sources of infection, and we are already starting to hear speculation in this regard.

“While these details are becoming known and with greater certainty, public health authorities are justified in taken a cautious approach to prevention and control strategies, and have the challenge of making big decisions in the face of key knowledge gaps and rapidly changing information.”

No conflict of interest.

Associate Professor Patricia Priest, Department of Preventive and Social Medicine, University of Otago, comments:

“Screening at the border seeks to identify people who are infected and could pass that infection on to others, so that they can be isolated until they are no longer infectious, and treated as appropriate.”

What is best practice in border screening (e.g. self-reporting, thermal imaging)?

“Screening arriving travellers seems intuitively like a good idea but there is no one ‘best practice’ in border screening. Providing information about symptoms to arriving travellers – what to watch out for and how to seek healthcare if symptoms develop – is a straightforward and reasonable ‘first action’ whatever the infection. However, deciding whether to screen by asking questions and testing those with symptoms, thermal imaging, etc, requires consideration of a number of issues (see below).”

How effective is screening in detecting infection (appreciating there some unknowns around the virus)?

“For most respiratory infections, screening all arriving travellers is unlikely to prevent the introduction of the disease into New Zealand. Highly targeted screening may be useful in some cases. Unfortunately it is never possible to be sure whether border screening will be effective early on in our understanding of an emerging virus, because we need to know how it affects people and the way it is transmitted. Other important factors are the likely volume of potentially infected arriving travellers, and the other potential uses of the resources and people who would be carrying out screening. We have to use the information we do have to try to work out whether, on balance, the benefits of screening will outweigh the costs.

“Some examples:

“If the proportion of arriving travellers who are infected with the virus is very small, then unless the virus causes very specific symptoms that differentiate it from other infections, the balance of cost and benefit is likely to tip in favour of not screening.

“Most respiratory viruses cause symptoms that are very similar to each other, so it is not possible to differentiate 2019-nCov from other causes of coughs and colds by asking about symptoms or thermal imaging. However, if we are very concerned that the virus causes very severe disease we might accept a low pickup rate, if by doing so we have a reasonable chance of preventing the virus spreading into the community.

“This consideration comes into play when thinking about focussed screening. For example, direct flights from Wuhan, where the majority of cases are, would have been more appropriate to screen than flights from Australia, where widespread human to human transmission is not occurring and the chance that any of the very many arriving travellers is infected, is extremely small. It is important to be clear that even in Wuhan, the vast majority of residents are not currently infected, so the chance of picking up someone infected with the virus is still pretty small.

“If everyone who is infected with the virus has a high temperature, thermal imaging at the border would be useful in identifying them so that they can be treated and isolated, and thus prevent spread into the NZ population. On the other hand, if most people who have the virus do not (yet) have a high temperature when they come into the country, thermal imaging will not detect most of the people who may go on to infect others.

“At present, 2019-nCov is thought to have an ‘incubation period’ of about two to 10 days. This is the time from when someone is infected with the virus until they develop symptoms. If the infected person (who doesn’t yet know they’re infected) travels during that two to 10 day period, they will not have a high temperature on arrival at a NZ airport and so will not be detected with thermal imaging.

“It is worth bearing in mind that people who are sick are generally less likely to travel, so people who have a fever before departing are probably quite rare. So the people who could be detected by thermal imaging at the airport are the very small proportion of infected people who move from not having symptoms to having symptoms, over the period that they’re on the plane. This is why thermal imaging is not actually particularly useful for border screening, in most circumstances.

“If everyone who is infectious (i.e., can pass the virus on to others) has symptoms, then asking about symptoms at the border will help to pick up those people so that they can be isolated and treated. People who do not yet have symptoms cannot be detected by these means, so providing good information for them about what to do if they develop symptoms is crucial, so that they can be identified promptly and treated and isolated once they are sick, minimising the chances that they will pass the infection on.

“If it is possible for people who don’t have symptoms to pass the virus on, it becomes much more difficult to prevent spread in the population. At this stage there are a small number of situations where this is believed to have happened for 2019-nCov, but if it turns out to be common then screening at the border is unlikely to be effective enough at identifying people who might pass the virus on to others are to justify the cost. The resources that would be required for screening may be better deployed to ensuring that people who become sick once they’re in New Zealand can access health care and testing for the virus quickly and easily.”

What other measures can be employed to limit the introduction and/or spread of an emerging disease in the New Zealand context?

“While screening a large number of arriving travellers in the hope of identifying infected people may not be cost-effective, airlines are required to inform public health authorities at the destination if a passenger becomes obviously ill en route. Those passengers can then be tested and, if appropriate, isolated to prevent them infecting others.

“As noted above, ensuring that people who become sick once they’re in New Zealand can access prompt testing and treatment (if available), and isolation, is important in limiting spread. In this case, health services will need to ensure that interpreters or staff who speak relevant languages are easily available to facilitate this.

“For respiratory viruses such as 2019-Cov, standard respiratory hygiene rigorously applied is the best way we have to prevent infection from being introduced and spread. Cover your mouth and nose when you cough or sneeze (use a tissue which you throw away or clean hands immediately afterwards); clean your hands regularly by thorough washing and drying or using hand sanitiser; avoid close contact with anyone who is coughing and sneezing, and if you’re feeling unwell, avoid going to places where you will be in close contact with others; stay home if you’re sick!”

No conflict of interest.