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Catching and spreading the flu

Find out how the flu spreads from person to person, and who is at the greatest risk of getting complications of the flu. Rishi is a pediatric infectious disease physician and works at Khan Academy. These videos do not provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read or seen in any Khan Academy video. Created by Rishi Desai.

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  • What was the word he said at when he was talking about the diabetic person? "I've drawn for you now someone with a ( ), which is diabetes, meaning they have some medical condition."
    (19 votes)
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  • hopper jumping style avatar for user jessica
    Are you equally contagious to others during the entire flu (Jan 10-17 in the case of the example in the video)? I grew up thinking that you are most contagious at the beginning of the flu, and less contagious at the end. Is that true?
    (19 votes)
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  • leafers ultimate style avatar for user eightsquare
    I can understand why pregnant women and the elderly are at a high risk of catching the flu, but why are diabetics at high risk too? Isn't diabetes related to another system altogether?
    (12 votes)
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    • old spice man green style avatar for user Alf Lyle
      Diabetics have a hard time controlling their blood sugar levels, and in extreme cases this can lead to death. The lack of appetite, fatigue, and changes in activity levels associated with the flu as well as the body's sometimes extreme response to the infection put a severe stress on maintaining control of blood sugar levels. This instability in blood sugar levels makes it much harder for a diabetic to deal with the complications of the flu. Since these risks are reduced by getting a flu shot, it makes especial sense for diabetics to get one.
      (17 votes)
  • marcimus pink style avatar for user Nadine
    Pregnant people are in the high-risk category and can develop complications, but would there be any complications of the flu that would effect their unborn child?
    (4 votes)
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    • old spice man green style avatar for user Alf Lyle
      Any distress to the mother will affect the unborn child. The mother's body does try to shield the child at the expense of the mother, but such shielding can never be perfect. Also, since at times the flu can lead to fatal complications to the mother, the child will die as well unless it is well enough along in development to survive a Cesarean section.
      (6 votes)
  • purple pi purple style avatar for user emilymorphew
    At he talks about RNA. What is RNA?
    (2 votes)
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  • leafers seedling style avatar for user joyaltheagallen
    hey I am the users son and I have asthma and I always wanted to know how 2 get rid of asthma for good cause I can't stand taking puffers eny more! >:|
    (3 votes)
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  • blobby green style avatar for user Michael Rawson
    How long after contamination does it take for symptons to appear?
    (4 votes)
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  • female robot grace style avatar for user Anna
    okay one time a couple of years ago I felt awful. it was from october 23 to november 23. I didn't get a flu shot ever because I don't think the vaccine is useful for really good immunity. the very first day I had sore throat and stuffy nose as well as a cough. I didn't have many constitutional symptoms. I might have had a fever but that is about it. I kept feeling like that for a month. I know that the range of time that you can have the flu is 3 days to a few months. the range you can have the cold is somewhere in a week. I was sick for a whole month though and then I felt better. I knew I had ILI and I was wondering if I had mild flu for a month. also I didn't get a flu test but I knew it was likely to be influenza.

    And I didn't have any symptoms of a secondary infection from another virus or a bacterium causing viral or bacterial pneumonia respectively, just the primary infection.

    I have a few questions.
    1) Could I have had viral pneumonia caused by the same virus that lasted much longer than the initial infection without realizing it?
    2) Can I do anything to prevent myself from having viral pneumonia from the same virus or a different virus besides taking antivirals which only do good during the first few days of the infection?
    (4 votes)
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    • hopper cool style avatar for user SofiyaMarkova
      1.No. the same influenza strand could not cause a month long infection and you also can’t be infected with the same exact virus. “When you fall ill, your immune system creates antibodies specific to the strain of virus you have. Those good guys stick around to make sure you never get the same exact virus again” (Josh Miller, D.O.)
      What most likely happened is you got different viral infections because your immune system was weakened from the flu you original got. “If someone catches another virus on the tail end of their flu, they may continue to experience lasting symptoms of influenza such as exhaustion, sneezing, coughing and congestion”. (Dr. Robert Strang).
      You are saying you did not have another virus, but how would you know that? “Flu viruses continually change over time. This constant changing enables the virus to evade the immune system, so that people are susceptible to the flu throughout life”. It could have been the influenza virus but of a different type. It would make sense for you to have the same symptoms.
      But then again, people can die from the flu so their symptoms would last a long time.





      2. You can get vaccinated against the viruses. It is best to keep clean (wash hands and use sanitizer) so that if the virus gets on you it is washed away or killed before effecting the body, eat healthy and get enough sleep so your body is not weakened in which case the virus will have an easier time effecting the body, be mindful of who and what you touch as a preventive measure, and boost your immune system through hydration and cold showers along with many other techniques.
      Tips on preventing viral infections: https://www.verywellhealth.com/preventing-colds-and-flu-2966798
      Tips on strengthening immune system: https://www.health.harvard.edu/staying-healthy/how-to-boost-your-immune-system

      Sources:
      https://abcnews.go.com/Health/Wellness/fight-off-flu/story?id=14956614
      https://www.ctvnews.ca/health/have-a-month-long-cold-it-s-probably-not-the-flu-1.3255473
      (1 vote)
  • leaf green style avatar for user es2295
    Is feeling flu-like symptoms for 3 to 7 days assuming that one receives antivirals? Or is it 3 to 7 days regardless of whether one receives treatment or not?
    (2 votes)
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  • leaf green style avatar for user Elias Nafziger
    Can you infect people with the flu after you caught it and recovered? If so, for how long?
    (1 vote)
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    • male robot johnny style avatar for user Cheenu Tiwari
      By the time you feel better, there are still a few flu viruses remaining in the body (simply because they have not been eliminated yet). The contagious period lasts from 5 days to a week after diagnosis, and it can be even longer in children. So if you recover from the flu within the time span of 5-7 days or earlier, you can still have a chance of spreading viruses. I believe this might be one of the more contagious parts of the flu progression in the body because you are better and therefore are more likely to have contact with others.
      (3 votes)

Video transcript

So today's January 11, 2013. I'm just going to circle the date on my little calendar here. And let's say I came home from work and I just felt really lousy, just awful. Fevers, sore throat, cough, body aches, you name it. This is the first day I've been feeling like this. And up until now, since the new year started, I was feeling really great. I had no symptoms. I was going to work. Feeling myself. So all these days I was feeling good. And then all of a sudden the 11th hit and I just got, all of a sudden, these symptoms. So I'm already suspecting the flu based on what we know. It started abruptly. I've got the symptoms for it. And a few questions start popping up in my head. The first question I want to know is, when can I expect to start feeling better? That's usually the first thing people want to know. So let's think about what we know about the flu in terms of how long the symptoms usually last. Because that's going to help us predict when I can expect to start feeling myself again. So we know that usually symptoms last for three to seven days. So I'm going to say, OK, all these days I'm going to expect to feel kind of the same maybe. I might start feeling a little bit better by the 16th or 17th. But that would be seven days. So these are the days I can expect to feel kind of lousy. And on average I should start feeling myself again maybe by the 18th and 19th. I should start feeling the way I normally do. So according to this calendar I would start feeling better by January 18. That would be my target date. And this isn't exact. This is just a rough idea. So what's the next thing that people usually try to figure out about the flu? They always want to know, who did they get it from? They always want to figure out who the culprit was. Who gave the flu to them. So I'm no different. I want to know who did I get it from. And so I think back and I say, well, I felt good on the 10th and I felt pretty lousy on the 11th. And your instinct might be to say, well, of course I probably got it on January 10. On Thursday. But, in fact, you have to go a little bit further back. Sometimes you can get it back as far as four days. So I'm going to circle the days that I could've potentially gotten the flu from somebody. And it turns out it could've been any time this week. So I'm going to write that down. So January 7th to January 10th. That's the window in which somebody gave me the flu. Now how do I know that I got it from somebody? Maybe I got it from the doorknob. Or maybe I got it from the remote control that someone was touching. And those kinds of environmental objects, sometimes you can get diseases from there. But with the flu you generally get it from another person. And the reason is, is because you've got this RNA that's protected by an envelope. Remember this green layer here, this double layer, is a lipid or a fat bilayer. It's got two layers of lipid or fat. And this is what we've been calling our envelope. This is the envelope. Now because it's got an envelope it means that the virus is actually more sensitive to the environment. The main way, then, that the influenza virus will get you sick is when you get it directly from another person because this envelope actually makes it very sensitive to the environment. It doesn't really do well when it's out in the environment by itself. So usually you get it directly from somebody. Maybe they cough or they sneeze. Maybe they get it on their hands and they shake your hand. Usually directly from another sick person. So really if I want to know where I got it from I need to brainstorm and think, who did I encounter between January 7 and January 10 that was sick? Now I also want to know, who could I've given the flu to? I'm a conscientious person. I don't want to give the flu to other healthy people if I can avoid it. It turns out you can actually spread the flu-- I'm going to circle it in purple here-- one day before you even have symptoms. So on the 10th of January, this is the day before I was sick, when I was actually feeling really healthy, I could have already been spreading the flu to other people. On that day. On January 10. And of course all these days when I'm sick I could also spread the flu. And that's more intuitive. Because I've got sneezing and coughing and other symptoms. But the interesting one is that on January 10 through the 17 I could have actually spread the flu around. So January 10, which is again a day before my symptoms through the 17th, I could have started spreading the flu. So to know exactly who I gave the flu to I've got a really brainstorm and think well who did I interact with on January 10th. Starting with that date. Well, of course I see my family every day. So family. And I'm a worker, an employee. So my coworkers. I would see them. And there are other folks, too. Like friends. I may, maybe not yet, but perhaps I might have dinner or meet up with some friends. Or I might actually even see some strangers. Sometimes I like to take the bus and I may see some strangers or I might shake someone's hand randomly. And so these are all the different folks who I've got to brainstorm and think about in terms of who I might give the flu to. Or who I might have already given the flu to. Maybe yesterday, January 10. Now let me actually bring up a little bit more canvas. Make some space. And think about these groups of people who I may interact with. In terms of family, for me, my closest family is my fiance. So I live with my fiance and I'm going to draw a picture of my fiance here. And my fiance is generally healthy. And so that's her right there. And then of course there are some other folks. Let's say some coworkers. Maybe I have a coworker-- I'm going to do in a different color-- who is over here also feeling pretty good. And looks healthy. But actually has diabetes, which is an important medical condition. And let's say I have some family friends. I'm going to draw a friend here. Here is my friend. And my friend happens to be pregnant right now. So this is my friend and she is pregnant. Over here. And she's got, of course, then, a little fetus inside of her. So this is my pregnant friend. And my pregnant friend has a two-year-old daughter. So a little two-year-old daughter over here. Two-year-old and my friend herself is pregnant. So I've got my coworker with diabetes. I've got a pregnant friend and a two-year-old daughter. And finally, let me actually go to strangers. Let's say I was actually on the bus. Or maybe I'm going to ride the bus. And here's a stranger on the bus. And this stranger is in a wheelchair. This is a wheelchair here. So this is a stranger who is riding on the bus with me one day and perhaps I help her off. And she thanks me by shaking my hand. So perhaps this elderly lady shakes my hand. And she's a stranger to me, but now I've potentially given her the flu as well. So while I had the flu I actually came into contact with some people that we would consider high risk. I've drawn for you now someone with a comorbidity, which is diabetes, meaning they have some medical condition; someone who is pregnant; a young child; and someone who's very old. And of course over here we have my fiance. And she's healthy and has no medical conditions. But do you think she's going to be too happy if she finds out that I gave her the flu? Probably not. So she's not going to be too happy with me either. So it's really important for me to keep all these different people in mind and know that I don't want to give other people the flu. Especially people that are high risk. These are high risk individuals. So why do we care so much about these high risk individuals? Well, it's because they develop complications of flu. And this is what it really boils down to. You remember we initially talked about all the hundreds of thousands of people in the US and around the world that get hospitalized for the flu. And then the numbers of people that die from the flu. Well, overwhelmingly it's people in this group. This high risk group. And the things that they get, the kind of complications they get, are many. Actually, flu leads to many different types of complications. And I'm going to draw out just a few of them for you. I don't want to give you an exhaustive list. But I want you to at least get an appreciation for the kinds of things we're talking about. So, for example, let's say these are your lungs. I'm drawing two branches of your lungs. And this is going to your left lung and the other branch is going to your right lung. So this is your trachea splitting up. And you know that the flu, the influenza, is going to affect the cells in your respiratory tree. So it's going to affect these cells and it's going to cause inflammation. You're going to get a big immune response. And if that response is really big, let's say you have a big response, and if it's around these airways here, these bronchioles-- let me actually extend this out a little bit, so you can at least appreciate where the arrow's going. If the response is really strong in the bronchioles, we call that bronchitis. So someone might actually develop bronchitis as a result of getting the flu. Now someone else might actually have a big inflammatory reaction in these little air sacs. Your lungs end in thousands and thousands of little air sacs. And if that happens, then you might call that pneumonia. You might say, well, this person has pneumonia. Finally, you have smooth muscle. Actually, lots and lots of it. Smooth muscle that wraps around the bronchioles. And sometimes with the flu you actually can trigger twitichiness of that smooth muscle. It starts spasming. And when that happens we know that sometimes as an asthma attack. So you can actually get an asthma attack related to the flu. So all sorts of things like this can happen. And it's awful. These are things that can actually land you in the hospital. Or can cause death, as well. So these are the kinds of complications. And there are other ones. Things like ear infections and sinus infections and many, many other things as well. But here I just wanted to show you a few of the complications that people get. And show you and remind you that it's usually the high risk people that you have to worry about.