>> Welcome back, everybody, to Inside Infection Control, our video blog here at CDC's Project Firstline. I'm Abby Carlson, I'm an infectious diseases doctor at the CDC. And it's great to have you here today. You may have noticed that a lot of the infection control recommendations for COVID-19 apply all the time, not just when you're caring for a patient that you know has COVID-19 or that you think might have COVID-19. Why is that? Why are steps like source control important all the time? It's because we know that many people who are infected with SARS-CoV-2, the virus that causes COVID-19, don't actually know it, because they aren't feeling any symptoms. They don't have fever or cough, shortness of breath, or other signs of disease. And even though they don't look or feel sick, they can still spread virus to other people. How does that work? On an earlier episode of our video blog, we talked about how viruses make you sick. When you feel sick, like with a fever and your cough, that's your immune system that's kicking in to fight the virus. You can check that episode out from our details. We've put a link to it as well in the comments. So, if you want more information on that, follow up there. But what's important to remember is that you can be infected with the virus, and your immune system can still be working, but you might not feel sick. You may have been infected recently, and you haven't started feeling sick yet, but you're going to in a couple of days, that is called presymptomatic infection. Or you may be infected and you will never feel symptoms at all. That is called asymptomatic infection. It's not clear why some people have milder cases of COVID-19 than others or why some people are infected with SARS-CoV-2 and never show any symptoms. But either way, when you're in this state of having the virus but not feeling sick, you still can spread that virus to other people and make them sick. How? Well, the virus in your body is there making copies of itself in your cells and spreading around. So, it's in your respiratory droplets. And those droplets come out filled with virus when you breathe, talk, cough, or otherwise push them out of your mouth and nose. Like when you're yelling or you're singing or exercising hard. And those respiratory droplets will spread places. They can be breathed in by others, and then the virus can start attacking that person's cells. Or they can fall on surfaces where they can be picked up and spread that way. Just one thing to note, although we're talking about COVID-19, it definitely is not the only disease that spreads from people who are infected but aren't showing any symptoms. Another really common one in healthcare is influenza, or flu. And it's a problem every year. So, to sum it up, what's important is to keep doing the recommended infection control actions, like masking for source control, to keep that virus from spreading, even if you don't know if you have the virus, and even if you aren't feeling sick, that way you're still protecting other people by having a mask on. As always, thanks for joining us. Please be sure to follow up with us. We're on Facebook, Twitter, and YouTube. Or you can meet us on the web; cdc.gov/projectfirstline.