Have you guys been noticing that when they report the numbers of
covid on a daily basis that there's also this like
overarching number that seems to be a whole lot bigger
so for example they might report that there's only 29 active cases in one
place but there's over 300 per 100
000 also identified so how do we get to those numbers?
Well this is known as incidence versus prevalence and
what we're getting on a daily basis right now with our covid pandemic
is a lesson in epidemiology when it comes to reporting numbers based on
incidence and prevalence. So we're going to talk about those two factors
in this video, break down those numbers so they make sense to you
right after this.
Welcome back my name is Tammy and this is NurseMinder and on this channel we do
everything nursing so if you're new here consider subscribing below so that you
get the next video when it's released. Now before we head to the board so I can
kind of detail this up for you in pictures, I'm a visual learner I like to
see things, we're going to just first basically
define incidence and prevalence. So incidence is
the number of new cases PER a defined set of population over a determined amount
of time. So the new cases we hear those every
night, we had 157 new cases we had 86 new cases overnight.
That is one piece of information we need to identify
what the incident rate is. Now prevalence is really a factor of how many people
have it currently within the population overall. So let's go to the board and
just kind of look at those two things in more detail.
Now when it comes to incident rates we're looking at how many new cases per
a defined population and what that means in defined population is
that everybody who belongs in this category needs to have the
potential to become at risk or to move into a
diagnosis of whatever it is you're measuring. So in
this lesson we'll talk about covid but this could be tuberculosis, this could be
heart attacks, so if you were looking at heart attacks for example,
you would get rid of everybody who's under the age of 18 and maybe even under
the age of 30 and then that would reduce the
population size because four-year-olds don't have heart attacks.
All right so in this case because it's covid everybody is at risk we've had
no data that comes out to show that children are not at risk,
there's no difference between gender so far male and women are affected,
there's no ethnicity immunity based on where you live and where you
were born so everyone's at risk so the entire
population is in this defined set. So from here let's just
say this person this person and this person
become infected, we now have three new cases
in our population size of 10. So in order to create the risk factor so
say all of a sudden we had a mass group of people move into our community
and our community now is a thousand people we're going to multiply that by
1000 and that tells me that I have a
potential 300 people that will move from our defined population into
our new cases. So there's a risk that we can
identify and then we can plan to implement strategies to manage
the risk, just like we did with covid by making
sure we had enough staff and icu beds and ventilators.
That was part of the planning based on the risk that was assigned to it
and then we can also plan education, prevention, such as our swabbing and
vaccinations to meet the demand.
Let's just take these 10 people over here and let's just assume
or let's pretend for example's sake that they have decided
or they've come out with information that says anybody under the age of 10
is immune. We've never seen a case doesn't matter what we do
they just don't seem to get covid. So we're going to say that these two people
here are under the age of 10 so they no
longer count in our population base. They're not part of our defined
population anymore. so now I have a base population of only eight
people who are at risk of getting covid and moving into the
diagnosed cases. So we now have eight as our base population instead of ten
with that we're gonna say three people
become infected
so three out of eight will become affected if we multiply again by a
population size of a thousand
the incident rate the risk rate goes from
300 now to 375. The risk factor has increased because
the population size has decreased. All right so on September 7th
we have a 157 new cases in alberta so that's that new cases
for incidents what's the total population that's at risk in alberta is
4.428 million people. Now when we're talking
about this big of a number we'd like to break it down into per 100
000 people so when you do the math 157 divided by 4.428 million
times by 100 000 people you have an incident rate
of 3.5 people for every 100 000 in the province of Alberta
but as we know there are places that have higher incident rates
than others, some have zero cases some have hundreds of cases, so being
selective about the population that you're choosing for the area that you
live understanding how many new cases will
tell you what the risk level is to getting
that illness or disease. Now let's look at prevalence.
Now prevalence is different in the sense that it's looking at the number of
affected people, so this will include new cases but it
will also include the cases that were diagnosed yesterday where the person
hasn't recovered, 10 days ago if the person hasn't
recovered, and so this number will be higher
and it is over the total population not just that defined
subset all right. So let's look at covid numbers and look at prevalence
because this is what we often see in our map on line when we google those
numbers. Here we have an example of Vulcan county
this is September 7th here in Alberta. Note that they have a rate of active
cases per 100 000 and that is at 313 people. They only have 29 active cases
and the population size is only 9 245 so what do these numbers
really tell us? So we come back and look at prevalence,
remember prevalence is the number of people affected, and in that case it was
29 cases - that's how many active cases they currently have
right now, so remember active is new cases plus those who have been diagnosed
before, over the total population, and their
population was 9 245. So if we do
this math 29 divided by 9 245 and multiply that by 100 000 to represent
the prevalence per 100 000 people should that many people live in that country we
would earn that county, we would see they have
313
per 100 000. This again helps to provide information for planning
and to make sure that people are accessing the resources that they need.
But this doesn't tell the whole story. Remember that this is the number
affected and people can move in and out of this category
by recovery or death and we know that there are people who are dying
from covid and same thing with this total population
this can change with births and deaths. So that number is fluid as well.
So that is our lesson on incidence and prevalence, now when you're hearing the
nightly news you can go okay we have 157 new cases
but that's out of how many? and what does that look like for risk?
what is my actual potential risk if I was in a room of 100 people?
and of course prevalence looking to see where we're at currently with this
illness and that will help you to understand why
the planning is in place and why certain measures have been taken
to reduce the risk and to navigate the health challenges
that people are going to be coming up against.
Don't forget to comment below let me know what you've learned out about your
incidence and prevalence rate where you live. Is it as bad as where
I've just shared or is it better? let me know below. Until next time make
it a great day. Hey I know you're probably not ready to
get off your phone or go back to work just yet or maybe even turn the lights
off to go to sleep, so why don't you spend a little bit more
time here watching another video ;)