• Question: How important is it to find patient 0 in a pandemic such as COVID-19 ? And how would one go about finding/tracking patient 0?

    Asked by indigoblue on 28 Apr 2020.
    • Photo: Kim Liu

      Kim Liu answered on 28 Apr 2020: last edited 28 Apr 2020 8:41 pm


      Interesting question! I would speculate that Patient 0 is interesting for research purposes and learning about infection in general – there may be genetic factors which make some members of a population more efficient at carrying infection, or maybe even making viral mutation easier. Also, knowing patient zero will make modelling disease spread more accurate, and give a better idea of the source of the disease.
      I think being certain about patient zero is almost impossible for COVID-19 because a lot of carriers are asymptomatic; it is possible that the very first infected individual had no idea they were ill. However, I believe that contact tracing back to patient zero is most effectively carried by looking for the virus’ genetic material.

      I’m looking forward to reading what others will write! ~

    • Photo: Lindsay Robinson

      Lindsay Robinson answered on 28 Apr 2020:


      It’s important to find out where a pandemic has come from although to define it as patient zero or one particular person is maybe not as helpful. If you find where the disease has originated then you can study how it is transmitted and develop models to how the pandemic may progress. This allows planning for heathcare, lockdown strategies etc. You may be able to answer questions about whether or not it can be transmitted between species or how contagious it is. I’m not sure how you’d try to track down patient zero but I’d imagine it would be tracing common contacts and working backwards to the source. Defining an individual as patient zero had some ethical considerations because I don’t think it’s helpful to have someone become a scapegoat.

    • Photo: Melanie Krause

      Melanie Krause answered on 28 Apr 2020:


      I am a virologist but I don’t work on coronaviruses. I have just read an article in the Guardian with the leading German scientific advisor Christian Drosten, where he was asked the same question. This is what he answered:
      Q: Will it be useful to identify patient zero – the first human to have been infected with this virus?
      A: No. Patient zero is almost certain to have acquired a virus that is very similar to some of the first sequenced viruses, so it wouldn’t help us solve our current problem. I don’t think you could even argue that it would help us prevent future coronavirus pandemics, because humanity will be immune to the next Sars-related coronavirus, having been exposed to this one. Other coronaviruses could pose a threat – a prime candidate is the Middle East respiratory syndrome (Mers) virus – but to understand that threat we have to study how Mers viruses are evolving in camels in the Middle East.

    • Photo: Spyros Lytras

      Spyros Lytras answered on 28 Apr 2020:


      Great question! Finding a patient 0 is not very interesting and probably impossible. The way we track viruses nowadays is by looking at the virus genomes. All living organisms and viruses have a genome. You can think of this as a piece of text that defines this particular organism or virus. Viruses are very good at changing their genomes (what we call mutating). Most of these changes have no effect on how the virus spreads or infects people, but they are a great way of tracking how the virus moves.
      Imagine the virus genome as a set of colourful Christmas lights. The virus in patient 0 only has green lights. Now think that every time the virus passes through 100 people one of its lights can turn from green to blue, red or yellow. This means that the genome of all viruses that infected the first 100 (or so) people are all the same (all green lights). So even if we had a sample from patient 0 it would be very hard (nearly impossible) to know that this was virus 0, just because its genome would look exactly like that of the first 100 viruses.
      Looking at virus genomes, however, is very interesting for tracking how the virus progresses past patient 0. If the first two lights in a UK and a US virus are blue, but the same two lights are green in a virus from China then it’s more likely that this particular virus moved from the US to the UK (or the other way around).
      Things get more complicated since the coronavirus has about 30,000 of these fairy lights that you can compare, but this is the most modern way scientists use to track how the virus moves.
      So the patient 0 virus is not very interesting, because it looks very similar to all the early viruses in the pandemic. What is interesting is all the new cases, and seeing how the virus spreads in real time, so that it’s easier for us to stop it!
      If you’re really interested in how we track the virus there is a really nice (and colourful) website called nextstrain https://nextstrain.org/ncov/global that shows all the virus genomes we have and how they relate to one another! Some parts of the website can be a bit technical, but you can just browse through it by clicking on the different genomes.

    • Photo: Nina Rzechorzek

      Nina Rzechorzek answered on 28 Apr 2020: last edited 28 Apr 2020 10:18 pm


      Hi indigoblue – great question; I’m not a virologist so I point you to the latest evidence on COVID-19 (see link on this page). It is certainly interesting from an academic perspective to understand how patient 0 arose, how they got infected in the first place, and why they were susceptible to infection. There are many factors relating to the virus and the host (human) that will play a role in this, but ultimately an emerging zoonosis (disease that spreads between other animals and humans) can occur at any time, and it will happen again. However, in the face of an active pandemic, I think resources are better spent on controlling the spread of the virus, understanding how it is transmitted, and how we can prevent infection, rather than on hunting down patient 0. Just as every virus is different, each time a new viral disease emerges in humans, the characteristics of patient 0 may also be different, so knowing ‘this’ patient zero may not predict aspects of the next one. Once the pandemic is under control, identifying and controlling new ‘clusters’ of infection as quickly as possible will be critical – and that requires testing, tracking, and tracing infections and any contacts infected people may have had with others. This is how we will have to control this disease until an effective vaccine is available. Although several aspects of COVID-19 may be relevant to future emerging diseases, the vaccines currently in development cannot protect us from every new emerging viral disease in the future. So, some of the best lessons we can take away from the current pandemic are how to prepare better for managing the next outbreak (including how to halt transmission early-on, how best to coordinate resources and personnel, and how to make a vaccine as quickly as possible). The viral ‘genomic landscape’ is changing all the time; we need to be able to respond and adapt quickly, which means having more flexible lifestyles and (like all good science) plenty of contingency plans!

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