Why COVID-19 Contact Tracing Is Important to Containment
Originally published by: Forbes — April 17, 2020
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Editor’s Message: One of the primary tools medical professionals are using to follow and contain the spread of infectious diseases like the COVID-19 Coronavirus is something called “contact tracking.” This is a multi-step process of trying to ascertain who a positively-identified infected person came in contact with while they were contagious. This is likely a term readers will hear more and more often as governments consider viable strategies for repealing “stay at home” orders. The follow article provides an in-depth look into how contact tracking works and why it is a vital tool in the fight to contain the spread of disease.
Vice Admiral Mark Mellett, Chief of Staff of Ireland's Defence Forces (left) and Paul Reid, CEO of Health Service Executive (HSE) with Defence Forces cadets who are being trained to assist with the staffing of the call cente handling contract tracing for coronavirus patients at Dr Steevens' Hospital in Dublin. (Photo by Brian Lawless/PA Images via Getty Images)
Contact tracing may sound like taking your contacts out of your eyes and then drawing circles around them. But that’s not what the Centers for Disease Control and Prevention (CDC) and different public health officials are talking about about when they are referring to contact tracing. It is a public health technique that’s been around for a long time, much longer than selfies, smartphones, apps, and hipster beards have been around. However, it is also what’s needed to help tackle the COVID-19 coronavirus pandemic. And it’s not as easy as moving your pencil around your lenses.
In this tweet, Robert R. Redfield, MD, Director of the CDC, indicated that contact tracing will be an important part of the response strategy to the COVID-19 coronvirus, otherwise known un-affectionately as the severe acute respiratory syndrome–related coronavirus-2 (SARS–CoV-2):
As we begin the process of Opening Up America Again, we will be aggressively focused on early #COVID19 case recognition, isolation, and contact tracing. These are the fundamentals of public health that we continue to implement to keep our Nation open. pic.twitter.com/Hu5svECDem
— Dr. Robert R. Redfield (@CDCDirector) April 17, 2020
The concept of contact tracing is fairly straightforward. When someone is discovered to be infected with a certain pathogen (that is, a certain disease-causing microbe), you then try to determine everyone whom that person may have had effective contact with while the person has been infectious. And everyone means everyone.
If you refer to this person as the index case, which is the person of interest who may be spreading a disease, the goal then is to identify everyone whom that index case may have already infected. It can also identify who may have infected the index case in the first place so that you can possibly do a contact tracing for the person who infected the index case. All of this will allow you to draw a map or diagram of who infected whom. Or who was infected by whom. Such a diagram can then help determine what needs to be done next to prevent the pathogen from spreading any further by isolating, quarantining, or treating all of those who may be infected before they can spread the microbe to others. But more on this later.
So how do you do contact tracing as part of a test-trace-isolate strategy? Follow these steps:
Step One: Identify the index case.
This is the “test” portion of the “test-trace-isolate” strategy. A person is an index case only if you know that the person has the infectious disease. If there were a “turn-you-into-a-cat-wearing-a-sailor’s-hat” infectious disease, it might be easier to spot an index case. However, for most infectious diseases, especially COVID-19, it is a lot harder to detect a real case without actually doing testing.
Step Two: Define an effective contact.
The next step is to define what constitutes an effective contact for the particular microbe of interest. An effective contact is one in which transmission of the infectious pathogen could have possibly occurred. The definition depends on the infectious disease and how specifically it is transmitted.
For example, if the infectious disease is a sexually transmitted disease (STD) like chlamydia or gonorrhea, an effective contact is not just saying hello to each other or exchanging a firm handshake loaded with innuendo. You actually have to get to at least third base with the other person, meaning have sex and not play a weird one-on-one baseball game. Therefore, if the index case has an STD, don’t count everyone whom that person may have passed at the grocery store, library, and workplace, unless, of course, that person is strikingly promiscuous. Only count those people with whom the index case got it on, did the nasty, bumped uglies, or whatever euphemism you want to use for having sex.
For a respiratory virus like the COVID-19 coronavirus, an effective contact is a lot broader than it would be for an STD. An effective contact could be coming within six feet of the index case, having physical contact with the index case like exchanging a handshake, or touching the same object such as a doorknob or Chris Hemsworth’s biceps without washing your hands afterwards. For the COVID-19 coronavirus, determining an effective contact can be more challenging since it’s not yet completely clear how contagious the virus may be and what are all the ways that it can be transmitted. It certainly seems to be more contagious than the flu.
Step Three: Determine the time frame during which new infections could have occurred.
Once you define what is meant by an effective contact, try to determine the period of time that you need to walk backwards to identify and count all the effective contacts. This depends on how long ago the index case could have been infected and then become infectious.
So let’s figure out how much time could have passed after an index case was initially infected. The first phase is the incubation period, which is the time between when the infection initially occurred and when the person becomes infectious, that is, able to infect others. For the COVID-19 coronavirus, the incubation period seems to be between two and 14 days.
Ah, but then you’ve got to count the time between the person becoming infectious and then developing symptoms. This may be anywhere between a day to several days. This is a dangerous time as far as spread of the virus is concerned. Essentially, the index case has a secret that even he or she may not know yet. The index case doesn’t have symptoms so may make little effort to stay away from others but can still pass along the virus. At the same time, others may say, “hey index case, you look healthy, let’s go about our regularly business and exchange hugs and yell ‘wooo’ at each other while spewing droplets into each others’ faces,” except that no one is really named “index case.”
In fact, a study recently published in Nature Medicine found that people may actually be most infectious right before symptoms appear, based on the amount virus detected in samples from people’s throats. In fact, the study authors estimated that 44% of people got their infections from people who didn’t have symptoms at the time.
Finally, you got to estimate how long the index case has had symptoms. All in all, the length of time since the index case first got infected will be:
=Incubation period + Length of time asymptomatic but infectious + Length of time with symptoms
And the length of time that the index case could have infected others will be:
=Length of time asymptomatic but infectious + Length of time with symptoms
If then the person was asymptomatic but infectious for two days and then had symptoms for seven days, then you want to determine all the possible effective contacts that the index case may have had for the past nine days. Basically, you ask the index case to recall every person he or she may have come into closer contact with over the past nine days.
This gets even more complicated if the index case happens to test positive for COVID-19 coronavirus but hasn’t developed symptoms and may never end up developing symptoms. As I wrote previously for Forbes, close to 20% of everyone infected with SARS-CoV2 may never develop symptoms. In this case, you’ve got to try to estimate the length of time asymptomatic but infectious by the following:
=Time since infected - incubation period
Step Four: Interview the index case to identify all of the potential effective contacts.
Oh, memories, misty water-colored memories. That’s what this step may rely on when you interview the index case. The index case will have to recall exactly whom he or she may have had an effective contact with during the aforementioned time frame. That may seem easy, except that it’s not.
Again this is trying to figure everyone, that’s everyone, whom the index case may have gotten within six feet of, exchanged physical contact, and touched the same objects within the time period during which the index case may have been in infectious or contagious. Heck, it can be difficult remembering what food item you just put in your mouth and if it was actually a food item, let alone where exactly you went and whom you encountered. The interviewer has to be skilled at eliciting memories by offering the right prompts such as, “ok, how exactly did you get on the gigantic stuffed unicorn? Was someone there to help you up there? If so, do your recall the person’s name and what he or she looked like?”
Step Five: Locate the potential effective contacts.
Once you’ve figured out who all these potential effective contacts are, the next step is to locate all of these folks, which ain’t necessarily easy. Finding that “dude, in the grocery store who was wearing the ‘I heart the Kardashians’ T-shirt and tried to grab the same rutabaga that I was grabbing,” isn’t much to go on when trying to locate contacts. Even if you are able determine a person’s name, tracking down that person can be like trying to finding a Kardashian T-shirt in many haystacks.
Once you find a potential contact, the challenges don’t necessarily end. That contact may disregard your inquiries or even be very suspicious of you. After all, random calls from strangers don’t always get the best reactions from people. You’ve got to earn the person’s trust so that he or she will be willing to comply.
Keep in mind that people may not be willing to admit that they had contact the index case. This can be especially problematic if there stigma associated with such a contact or having a disease. For example, this can be a major issue with STDs. This tweet (https://twitter.com/reesewaters/status/1250815749721141250) is reminder that not everyone is willing to admit that they may have crabs.
OK, maybe these aren’t quite the same crabs as the sexual transmitted ones.
Step Six: Isolate or quarantine all potential effective contacts.
The aim is to potentially isolate or quarantine all of these possible effective contacts as soon as possible. Isolation and quarantine are pretty much the same thing: keep a person away from having contact with others so that he or she can’t further spread the virus. The only difference is that isolation is for people who are known to have a disease and quarantine is for people who may have the disease. In either case, a person will have to stay away from all others until it is clear that the person is no longer infectious.
All of this is the “trace-isolate” part of the strategy, because “trace-isolate-or-quarantine” is a little harder to say. Speed is of the essence because any delay means that these potential effective contacts could in turn make effective contacts with other people who in turn can make effective contacts with others. You can see how things could rapidly get out of hand (and into nose and mouth.) Getting all potential effective contacts isolated or quarantined before they can spread the virus to anyone else is the way to break the chain of transmission and effectively contain the virus.
Typically, doing contact tracing requires people, lots of people. These folks have to be properly trained to do the different aforementioned steps. Again, all of this may sound easy if the index case has spent most of the time at home, except for one trip to the local market to fight for toilet paper. But the more active the person, the longer its been since the person first became infectious, and the more suspicous the people involved are, the more difficult the tasks. Moreover, convincing a person to be isolated or quarantined is not always the easiest thing to do.
Step Seven: Store, integrate, and analyze the contact tracings and contact network.
Remember that one set of contact tracings is just part of the broader public health picture and response to try to contain the infectious disease. Therefore, public health officials need to collect the different contact tracings that have been conducted in an area to establish how these tracings may intersect. For example, Bubba may have been exposed to several different infectious people such as when Karen demanded to see his manager, Felicia said bye, and Chad shared a story about his bros. From the different contract tracings, public health officials can then construct a unified diagram of the overall contact network. Think “six-degrees of Kevin Bacon” and you’ll realize that everyone is highly interconnected in different ways. A social network diagram, or sociogram for short in case you don’t have time to say “network dia”, is a graphical representation of how people are interconnected. It can use circles to represent each person and then a line between two circles if the two people have had an effective contact.
Here is an example of a sociogram from Kayla de la Haye, PhD, a leading social network analysis expert and Assistant Professor of Preventive Medicine at the Keck School of Medicine of University of Southern California (USC):
This is a sociogram of Grade 8 students and their friendship network. Each student is represented by a circle and lines between circles represent social connections. (Image: Courtesy of Kayla de la Haye, PhD)
This is a social network diagram of students in an eight grade with each circle representing a student and lines between the circles representing friendship. You can see how interconnected the network is. It also makes you feel bad for the circles on the side with no connections.
Step Eight: Integrate all of this with other responses to the infectious disease.
People take photos as the rooms at the Grand Hotel are illuminated to form the word "zero" after Taiwan reported no new COVID-19 coronavirus cases for two consecutive days, in Taipei on April 17, 2020. (Photo by Sam Yeh / AFP) (Photo by SAM YEH/AFP via Getty Images)
Test-trace-isolate should be part of an even broader response strategy. Based on the number of cases and deaths, both Taiwan and South Korea have been able to control the COVID-19 coronavirus much more effectively than other countries like the U.S. and U.K. Taiwan and South Korea have used a whole scientific system of responses that included early action, social distancing, and shoring up health care capacity as well as test-trace-isolate that fit together in a coordinated manner. To help with contact tracings, Taiwan and South Korea rapidly developed and used mobile technology to help identify index cases and potential effective contacts.
Now other countries are trying to follow their examples. David Phelan wrote for Forbes about how the U.K.’s National Health Service (NHS) is developing their own smartphone app to help with contract tracing. Apple and Google are pairing up to develop an app that can help identify if you’ve come into contact with someone diagnosed with COVID-19, as covered by Zak Dorfman for Forbes. Such apps can detect when your phone is close to someone else’s phone, assuming that the other person is also using the app. In essence, these kinds of apps will be able to construct a social network diagram for all those using the app, showing who came into contact with whom. Then if a person enters into the app that he or she is infected with the COVID-19 coronavirus, everyone who is registered as contacting that person will be notified. The utility of these apps will of course depend heavily on how many people agree to use the apps and keep their COVID-19 status updated. If the only people using the app are you and some guy named Winston who is 500 miles away from you, it’s not going to be very helpful.
Ultimately, such apps could facilitate contact tracing but won’t be necessary if enough people can be available to do the tracings. Regardless, until a vaccine or specific treatment for the COVID-19 coronavirus can be developed, test-trace-isolate will be an important strategy to help contain the virus and a key to “re-opening” the country. After all, how can you decide to relax social distancing when even a few infected people who aren’t isolated could easily lead to a new surge in cases?