Testing, contact tracing, and quarantining

Testing, contact tracing, and quarantining

This is the third installment in a series on COVID-19.

How do you deal with an epidemic?

A respiratory disease epidemic ends after each person consistently spreads it to fewer than 1 person, on average.  That can happen in many ways. You can choose not to try to stop it, depending on factors like its severity and method of spreading.  If it isn't bad enough and there is no immunity from getting it, it might be reasonable to just let it keep going, and just get used to it. Or maybe it is really bad, but still there is no immunity, so you still just get used to it and treat the symptoms, like with HIV.

You might also let it keep going if it isn't that deadly and people become immune once they get it.  Reaching so-called "herd immunity" takes enough people in the population having it that the remaining carriers have almost nobody to spread it to.  Current speculation is that COVID-19 would need 70% to 90% of people to get to this herd immunity.

So, you can learn to live with it.  You can reach herd immunity.  Or you can contain it.  If it is sufficiently bad, the normal approach to an epidemic is to figure out who has it and keep them from spreading it to others. How?  Test well, contact trace the positives to find where it came from and every contact they had, and quarantine all positives and possibilities. 

Testing

At this juncture, you want to test for the current presence of the SARS-CoV-2 virus.  Viral testing finds those with living viruses right now, as opposed to those who have had the virus at some point.  This is trickier than it might at first appear, as the testing has to differentiate from other viruses and do all sorts of other microbiology, science-y things, with virtually no room for error.  You might think that scientists around the world would work together on this, and you would be partly right.  But importantly wrong, as the US chose to create its own method of testing, and the first couple of months of attempts had major problems. And there are some indications those problems may not be altogether gone.

There is a much bigger problem with testing, which is the supply chain. You need the swabs to take the test, and the swabs are odd for a few reasons, including their long "poke the brain" nature; and the swabs are proprietary. You need the reagent, which also can run out, especially when the whole world is trying to get it. You need the transport media and the RNA extraction kits. And then you have to have the right devices to use the proprietary swabs and reagents.  And staff to do all of this stuff, while still doing normal healthcare.  And Personal Protective Equipment (PPE) for all your staff, which has its own supply chain problem. And the tests have to come back quickly enough to be useful.

Anyway, once you fix all of this, you have to keep fixing it, until you have a robust testing strategy.  You know this when you have a low positivity rate with a high number of tests (if you can agree on definitions, of course).  That means you definitely need to be consistently less than 10% positive (the WHO recommends 5%), and the lower the positive rate, the better.  

So, you fix the pragmatic issues of testing, and move on.

Contact tracing

Once you have found a positive, you hire a bunch of people (like 100,000 or maybe significantly more for the US) to act like virus detectives and find everyone these positives had contact with.  You definitely find from whom they contracted it, and you can keep going back until you reach someone you already knew.

This is pretty hard to do in a small epidemic with a relatively small group of infected, and it is basically impossible in a large one because there are too many possibilities to find the certain cause.

And there are a lot of pragmatic concerns here, too, like sharing information with others tracing. And having enough contact tracers. And people answering the phone and telling you the truth.  It turns out that many people don't.

And once you find them, they need to quarantine.

Quarantining

The CDC says you should isolate for at least 10 days since symptoms first appeared (or you tested positive if asymptomatic) and it has been at least 24 hours with no fevers, and symptoms have improved.  Keeping yourself away from everyone for a couple of weeks is hard.  First, you had to answer the phone, and then you had to agree to do it.  You have to not go to work and not spend time with others. If the number of people that have to quarantine is small, everyone else can pitch in and help, like bring you food and groceries, etc.  Of course, you may very well get or be sick. 

It turns out that lots of people don't quarantine, even when told to do so.

But, if testing, contact tracing, and quarantining work, this is the one sure-fire way to stop an epidemic.  But you need to get the number of people down to a small amount, and limit the amount of contact tracing needed.  How?

Shutdowns

When everything went crazy in China and then Italy, the rest of the world took notice. If people don't intermingle, there is less likelihood of spreading the disease, and fewer people to trace. Remember that an epidemic ends when each person spreads it to fewer than 1 person, on average.  That can be made a lot easier if everybody stays away from everyone else ... like the whole world quarantining.

But, of course, some people didn't actually quarantine.  Some couldn't, like doctors and firefighters and police. And some wouldn't.  But shutdowns absolutely decrease spreading the disease.

(Of course, that's not all they do -- there are lots of secondary effects that we'll discuss in a later post.)

Antibody testing

There is another relevant type of testing: Was I infected previously?  Antibody testing can be a useful mechanism to discover infection rates, herd immunity, specific immunity, and other nifty things.  Of course, they take supplies and PPE and need their devices and supply chains.  Oops.

Oh, and they need a working test.  And it helps if you know whether any immunity at all is conferred, and if so, what level of antibodies are needed, or even if whatever immunity is conferred by the antibodies at all.  Unfortunately, none of this has been true, and antibody testing hasn't yet been as helpful as many hoped (though it eventually will tell us much).

Dealt with!

So, if you shutdown everything for a few weeks, and when you come out of shutdown you have sufficient testing, contact tracing, and quarantining, and everyone follows a few simple rules, you can get an epidemic under control.  Or ... at least enough under control that it is manageable until vaccines are ubiquitous.

Everyone needs to follow those simple rules, though ....