[MUSIC PLAYING] EMILY GURLEY: Hello, my name is Emily Gurley, and I'm an Infectious Disease epidemiologist at Johns Hopkins Bloomberg School of Public Health. Today, I'm going to talk to you about the basics of contact tracing for COVID-19. Once you finish this lecture, you should be able to do a number of things, including describe what contact tracing is and how it can be used to stop transmission of SARS coronavirus 2. You should be able to define what we mean by a case of COVID-19, and also be able to define what a contact means. You should be able to explain the meaning and purpose of isolation and quarantine. You should be able to calculate how long a case should isolate and how long a contact should quarantine based on what we know about the infectious period. You should be able to describe the connection between the infectious period and isolation and quarantine, and importantly, you should also be able to identify high risk settings for transmission that might require extra action beyond regular contact tracing efforts. So let's talk now about contact tracing and how it's used for COVID-19 prevention. Every case of COVID-19 that's diagnosed requires action. We have to act, and there are a number of ways that we have to act. First, we need to support the person who is infected. It's important that we act to ensure that they have access to medical care and any social services they may need. They need to be able to access treatment. Right now, we only have basic supportive treatments available, but one day if we have other treatments or curative treatments, they would need to be identified so they can be offered those curative treatments. We also need to act to be sure that those cases are limiting their contact with other people. This is important, because someone who is infected can infect others. And part of our goal as public health practitioners is to prevent the spread of COVID-19. So when we diagnose a case, we need to find them, offer them medical support, and also make sure they're changing their behavior to limit their contact with other people to reduce the risk of transmission. Next, we have to also identify all the people that they may have infected. We have to notify them about their exposure and offer them some social services that they may need. If they develop signs and symptoms, we also need to make sure they have access to medical care and offer them treatment. And importantly, we need to limit their contact with other people. So once we find people who've been exposed, those people could become infectious and then infect other people. So if we can get them to change their behavior, we can limit transmission onward. So the basic idea behind contact tracing is that if we can limit contact between people who are infected and others, then we can limit opportunities for this virus to be transmitted, and this is vitally important for COVID-19. This is one of the best ways that we can limit the spread of this disease. Let's also recall the timeline of infection and infectiousness. So here we can see that someone has been infected. You can see in the orange line their incubation period, and that's the time between when they become infected and when they develop signs and symptoms. Then you can see in the blue line, after they develop signs and symptoms, how long they'll have the disease. And then in yellow, you can see, again, the time period that this person is infectious. And that means the time period when they can infect other people. This timeline shows that people can infect others up to two days before they themselves feel ill, particularly on the day of illness and throughout their illness period. Now, if we assume that someone was infected or exposed to this person and infected on the day that person became sick, if we assume they have a five day incubation period, they're going to become ill five days later. We can also think about their infectious period, which would begin two days before they became sick and would last throughout their illness period. So the point of contact tracing is to find those contacts and ask them to stay home so that they don't infect anybody else. And as you may recall, that window of opportunity to find them before they themselves become infectious and could infect someone else is pretty quick. And so this is important to keep in mind when you are finding contacts and tracing contacts. This whole system of finding cases and contacts has to happen on a very short timeline to be optimally effective. Isolation and quarantine, which we'll define shortly, can have a big impact on reducing transmission, because they serve to limit contact between people who are infectious and others. And as we know, stopping just one transmission chain can prevent many future cases. As you can see here, if each infected person infects two other people, an outbreak can grow very quickly. However, if we can stop just one of those people from being infected at each step, we can really have a big impact on the total size of the outbreak and reduce transmission. [MUSIC PLAYING]
