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Catching and spreading the flu | Infectious diseases | Health & Medicine | Khan Academy

November 18, 2019

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.


  • Reply alexandrenr January 12, 2013 at 5:39 pm

    does this apply to type B and C flu as well or mostly type A? thanks in advance!

  • Reply khanacademymedicine January 13, 2013 at 5:33 am

    Applies to Type B, but Type C is a much milder illness (more like a common cold).

  • Reply Prasenjeet Ghosh January 13, 2013 at 4:04 pm

    Thank you for the education. I love your channel – you make things so easy to understand.

  • Reply Prodon January 13, 2013 at 11:10 pm

    Great Job!

  • Reply Gila Atwood January 15, 2013 at 6:55 am

    enjoying all your presentations and it's very cool to turn something which could be just seen as personal misery into objective science, beyond ourselves.. thumbs up! Fascinating channel generally, learning a lot!

  • Reply sdm aji January 18, 2013 at 2:15 am

    Rishi, does your uploads help with the first two years of medical school, I am starting my first year of medical school next Fall, and I was wondering how much watching them is going to be related to what I am going to be learning in medical school and USMLE Etc….. Thanks in advance

  • Reply khanacademymedicine January 18, 2013 at 6:49 am

    They should help out with medical school and the USMLE…that's my hope. =)

  • Reply TheLordShinnok January 23, 2013 at 8:37 am

    I used to get sick every few months but not anymore

  • Reply khanacademymedicine January 30, 2013 at 11:40 pm

    It's good to clarify the different types of diabetes (or any disease for that matter: herpes, neurofibromatosis, etc…). I will be sure to clarify whenever the specific type of diabetes is relevant to the video. If I forget, please let me know! =)

  • Reply jazzandtapioca1 January 17, 2016 at 11:12 am

    I have a question i get colds nearly every mounth i currantly have one is it normal ?

    What do i do if its not normal?

  • Reply Doctor K May 12, 2016 at 6:04 am

    that pregnant friend tho haha … anyway great job..

  • Reply Bob Ebitz January 29, 2017 at 2:14 pm

    Flu is known to be spread by particulars in the air, by skin contact, and ingestion.

    Now look around you do you have a drink container at your work station, is the top open? Is the drinking/lip area completely covered?

    Tops with straws sticking out of and slurpply lids are a landing field for stuff, it’s a good thing to have a total closed top (like a stein lid) that can be removed and replaced to keep your drink safe.

    Think of having your own drink container and protector/lid/cover with no holes, that you personally clean.

  • Reply caatabatic January 20, 2018 at 4:13 am

    who else is watching this because they think they have the flu?

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