[MUSIC PLAYING] SPEAKER: Now let's talk about how SARS coronavirus-2 is transmitted between people. There are two main ways that SARS coronavirus-2 is transmitted between people that you need to remember. So as you know, infected people have the virus in their respiratory tract and their mouths, noses, and throats. Droplets and aerosols are two types of respiratory particles that come out of our nose, mouth, when we're talking laughing, coughing, sneezing, or even singing. And droplets are larger. Aerosols are smaller and can be quite small. But both come out of your respiratory tract. Sometimes you can see them when they're large, but sometimes they're so small and you don't really notice them. But they're there anyway. And if someone is infected with SARS coronavirus-2 then those droplets and aerosols that come out can have the virus in them. And then those respiratory particles, if they land on someone else's face, in their mouth, nose, or eyes, or if they're inhaled by someone else, they can infect someone else. If you're sitting close with someone-- if you're talking with them or you get a cough in the face or you're inhaling their exhaled breath, if you're sitting nearby someone, then the virus they shed can travel far enough to infect you. The second way the virus is transmitted that you need to know about is through contact with surfaces that have viruses on them. This kind of transmission is much less likely than through the respiratory droplets and aerosols, but it's still possible. So if those infectious respiratory droplets get on surfaces or they're on an infected person's hands and that person touches a surface like a table or a doorknob, they can leave the virus on that surface. And then the virus can survive or stay on that surface for some period of time. And it can contaminate the hands of other people. So if you touch that surface that has virus on it and then your hands touch your mouth, nose, or eyes, the virus can infect you that way. That's why hand washing and cleaning are also an important part of preventing transmission, because people can get infected through their hands. In hospitals, patients have procedures done that may increase transmission. But that's a specific setting. And we're really focused here, in this lecture, on how transmission happens in communities, in homes and workplaces, and out and about-- so outside the hospital setting. So as you already know, people who are infected with this virus will have infectious virus in their respiratory droplets and aerosols. So again, when you cough, talk, sing, sneeze, those viruses and those droplets can travel up to six feet, which is a pretty long way. And aerosols can travel even a bit farther. And those viruses again, can land and eyes, noses, mouths of other people, or be inhaled and infect them that way. And as we already mentioned, they could also land on surfaces. Aerosols can travel a bit further than larger respiratory droplets. And if you're in an enclosed space with limited air movement, then transmission can happen even further than six feet away. Others can Inhale those and be infected. And that's how transmission primarily happens. That's why mask use can be one great way to reduce transmission. This is primarily to keep infectious droplets and aerosols from contaminating the environment. So if someone who is infected is wearing a mask, then there are fewer infectious droplets and aerosols that would be coming out of their mouth and nose. Wearing masks is also a great way to prevent people from infecting others and can reduce the amount of virus that you're exposed to in an environment. Something to keep in mind is that SARS coronavirus-2 is transmitted very efficiently. So this virus transmits between people in ways that make it very difficult to detect and stop. People are infectious before they have symptoms. And so they may be infecting others and not even know it. Some people never develop symptoms. And so they could also infect other people without knowing that they themselves are infected. So it's important for us to test symptomatic people and identify who they've had contact with quickly, to try to limit the spread. This is done through contact tracing. And you'll hear more about in this course. Now that how the disease is transmitted, it makes sense that transmission is more likely to occur the closer the contact you have with someone else. So people who have physical contact with an infectious person or have close contact are more likely to be infected. By close contact, we mean people who are within six feet of the infectious person for 15 minutes or more. There's nothing magical about these thresholds, but these are guidelines where we know or have some good evidence that risk is higher. And why do we talk about six feet? Well, that's the distance that most of these infectious respiratory droplets and aerosols are most likely to travel. And 15 minutes means that you've been around them long enough so that you may have come into contact with some of these infectious particles. That's what we call a closed contact. And closed contacts may have never had actual physical contact with a patient. But they're close enough so that they could be at risk for transmission. People who share an environment with someone who's infected are at some risk for infection themselves. An example of a shared environment would be an office space, or even sharing a meal at a restaurant, if you're close enough to the person. If you're indoors where ventilation is poor, respiratory particles can travel even beyond six feet. And others sharing those kinds of spaces are also at risk. So sharing food, sharing bathrooms, that's another great example of a shared environment where infection can be transmitted. Sharing a bed is another way that transmission could occur, again, because you're in close contact or physical contact with someone who has the disease. For all these reasons, transmission is much more likely between people who live together. Because they're often having physical contact, as well as sharing spaces. So if living with someone who's infected increases risk of transmission, there are some types of living conditions that dramatically increase the risk for transmission. Sometimes we call these congregate housing settings. And it means essentially, when there are many people living in very close quarters. Prisons and jails are examples of congregate housing, as our group homes, dormitories, or shelters. These places are all at high risk for very quick spread of the infection, because people are living close together and sharing spaces. Nursing homes are a setting that represent a worst case scenario for COVID-19 transmission, because they're congregate housing situations where everyone is at high risk for infection and residents are at increased risk for severe disease. So nursing home residents are at high risk for severe disease, because they are older. They may have multiple underlying medical conditions. And they need multiple interventions, often such as feeding or assistance with toileting. That means they have frequent and close contact with other people. Staff are at increased risk of exposure and infecting residents if they become infected. And nursing homes aren't hospitals. So they're not set up to care for people with severe infections, and may not always have infection control protocols in place to limit spread. So these are places where we really need close intervention to reduce risk to residents and staff. [MUSIC PLAYING]
