Eli5; how we find “patient zero” when there is disease outbreak? (Like how they found who started the ebola outbreak in 2014)
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Contact tracing. Start with whoever has the disease right now, and use whatever info you can to determine who they’ve been in contact with during the past days/weeks/months – whatever the exposure/incubation period is. If any of those people also have or had the disease, repeat the process, and do it again and again and again until you get as close to the source as you can.
It’s easier to do this if the disease has a short exposure to symptoms period, a direct infection pathway, if the sypmtoms are serious and noticeable, and if there’s a decent health care system in place. It’s really hard to do this successfully if the symptoms are mild and it takes time for the illness to manifest.
First things first, Patient Zero was one guy, a specific patient who was “credited” with being the index case for HIV/AIDS. The general term for the first officially recorded case of a novel disease is “index case”, and it isn’t as big of a deal as movies often imply. It *is* helpful to trace the source of something like Ebola back to an animal reservoir, and from an epidemiological perspective you want to be sure that you’re at the end of the chain of infection.
In reality though you rarely know for sure who the index patient was overall or for a given outbreak, so it ends up being a bit de facto “who did health authorities notice first?” The Index Case is more of a result for how contact tracing and other epidemiological techniques work in practice than some sort of holy grail.
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The quick answer is that we don’t. The idea of patient zero is a misunderstanding that stems from the AIDS epidemic.
What people usually mean when they say patient zero though is the index case, which is the first documented case of an epidemic disease *within a population*. In other words, it’s not the person who started the pandemic or anything. That would be almost impossible to find out.
To find the index case though, you ask every known patient who they have had contact with in the time before they got sick, then you check if any of them have been sick and ask them the same question until you’ve found the common origin. Oftentimes there are more than one, especially with global pandemics like Covid.
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If someone hasn’t said it yet, this movie in the link below Snow portrays the father of epidemiology (how we map diseases), John Snow (no not GoT lol).
Essentially we use a link diagram….ask sick person where they routinely go, who they saw before they were sick, go to those places/people, and repeat.
-Only a BS in Public Health so not exactly an expert but we did do these as assignments during my time in school.
https://m.imdb.com/title/tt2061801/
Doctor to Patient 2: “Who’d you kiss?
Patient 2: “Patient 1”
Doctor to Patient 1: “Who’d you kiss?”
Patient 1: “Patient 0”
There’s you some Eli5
They try to figure out who the first person that got sick was. They ask the first people who got sick and work backwards until there is nobody left.
I saw a pretty cool show on this before. SHort answer they genitically test it. As they get results globally, using transmission rates, and mutations, the can show what cities it spread from etc etc..the show was pretty damn cool. They showed the previous years flu epidemic and where each of the outbreaks started, how it mutated where it travelled to etc, and were able to, obviously speak to people who had it to find out where they travelled from, when they noticed syptoms etc etc…quite a bit of detective work…
Gaëtan Dugas was alleged to have been patient zero and basically blamed for AIDS outbreak in the USA. This was later debunked
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