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This is an introduction
to epidemiology.
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Epidemiology is a word
that we hear often in nursing.
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But we don't always
know what it means.
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And because we don't
know what it means,
it can be a little bit scary.
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Today, I'm going to break down
some basic concepts
in epidemiology
that will help you
become knowledgeable,
and hopefully a little less
anxious about this big word.
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So let's first break it
down into three parts.
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Epi simply means being above.
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Demi, that's our population.
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Ology is the study of.
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So when we
bring it all together,
epidemiology is studying that
which is above what is expected
in the population.
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Epidemiology is
used to find the causes
of health outcomes and
diseases in our population.
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In epidemiology,
the public health nurse sees
the patient as the community
as the population.
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This means that individuals
are viewed collectively
as an aggregate.
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So let's take a look at
some common terms
that are important
in epidemiology.
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Let's start with incidence.
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Incidence is the number
of new cases of a disease
within a population
over a specific period of time.
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It's the number of newly
diagnosed cases of a disease.
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So for looking at the
incidence of a disease this year,
we're looking at the number
of new cases this year.
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Incidence is a measure
that allows us to determine
an individual's probability of
being diagnosed with the disease
during a specific timeframe.
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When we calculate incidence,
it's the total number of
new cases of a disease
divided by the number of
people at risk for that disease
in the population.
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So let's say we're
using epidemiology
to explore a specific
type of cancer.
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We know that over
the course of one year,
three people have been diagnosed
with this specific
type of cancer.
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This is out of a total
population of 200 people,
these 200 people are at risk,
but do not have cancer at
the beginning of the time period
at the beginning of the year.
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We use the three who are
newly diagnosed as the numerator,
and the 200 of total
population as the denominator.
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Based on this calculation,
we would say the incidence
of this type of cancer
in the population
was 0.015,
or 1500 people per
100,000 population.
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To better explain
this, imagine a sink.
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The fresh water flowing from the
faucet and remaining in the sink
represents the new
cases of disease this year.
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This is the incidence.
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Now remember this example
because we're going
to come back to it.
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Okay, let's move on and talk
about another important term.
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Prevalence.
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Prevalence is the number of existing
cases of a disease in a population
at any given point in time.
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This would mean
examining a specific disease
and learning how many cases
exist in the population today.
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Prevalence is a measure
that allows public health nurses
to determine a person's
likelihood of having a disease
at any given point in time.
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Prevalence rate is the total
number of cases of disease
existing in the population
divided by the total
number in the population.
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So let's continue on with our
example that we use for incidents.
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Now remember,
we found that for that one year
time period that we measured,
three people were
diagnosed with cancer,
that's three out of 200.
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Now let's imagine that
prior to that time period,
two people were
living with cancer.
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What we do here is simply
add the newly diagnosed
to those who are living with
cancer to create the numerator,
that would be five.
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We use the total population
or 200 as the denominator.
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Following this calculation,
we find that the prevalence of
this cancer within the population
is 0.025
or 2500 per 100,000
people in the population.
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So let's go back
to our sink analogy.
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Here we see that
there's already water
standing in the
bottom of the sink.
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This represents people who
already have the disease.
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That water plus the fresh
water pouring in from the faucet
which represents the incidence,
the new cases of disease.
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Combined, this is prevalence.
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Incidence and prevalence are
often confused with each other,
but as we just saw,
they're different.
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Incidence is the proportion
of individuals in a population
who develop a condition
during a particular time period.
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Prevalence is the proportion
of individuals within a population
who have a condition at any
particular or a moment in time.
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So incidence includes
new cases only.
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And prevalence includes
new and pre existing cases.
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When we're doing
our calculations,
this means that
the main difference
between incidence and
prevalence is their numerators.
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The total healthy population or
the denominator remains the same.
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Okay, so let's focus for just a
minute on only the numerator.
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The numerator of incidence
consists only of people
whose illness started
or was diagnosed
during that
specific time period.
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The numerator for prevalence
includes all the people
who are ill from
that specific cause
during that time period,
regardless of when the illness began,
and includes not only
the new cases again,
but also pre existing cases.
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So when might you use
one measure over the other?
Well, let's think
about this for a minute.
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Prevalence is based on both
incidence and duration of illness.
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A high prevalence of
disease within a population
might be the result
of high incidence
or the result of prolonged
survival without a cure.
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On the other hand,
low prevalence might
indicate low incidence,
or a disease process
that's rapidly fatal,
or has a rapid recovery.
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Prevalence is often measured for
a chronic disease, such as diabetes,
which has a long duration,
and the date of onset is
really difficult to pinpoint.
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On the other hand,
incidence is often used
with communicable diseases
such as influenza.
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Let me share an
example from a colleague
who worked to improve outcomes
for patients diagnosed with HIV.
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She was working in
the community at a time
when a new and effective
intervention was introduced.
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Because of this intervention,
fewer cases of HIV
progressed to AIDS.
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And because of that,
fewer people died.
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At the same time,
she was also running an
effective prevention program.
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So while incidents decreased,
now remember, that's the
number of new cases of disease,
prevalence continued to increase
because fewer people were dying.
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So in fact, an
increase in prevalence
and a decrease in incidence
showed improvement in the
community's overall HIV outcomes.
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Okay, time to
shift gears a little.
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Now we're going to talk
about morbidity and mortality.
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What is morbidity?
Morbidity is simply
another term for illness.
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Examples of morbidities
are heart disease,
Alzheimer's disease,
cancer,
traumatic brain injury.
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It's important to remember
that morbidity is not death.
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It's simply a
measure of illness.
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When people
experienced morbidity,
there's a disruption in their
body's ability to function.
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They may have physical deficits,
infections, or mental
health challenges.
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Morbidity rates are
simply a measure
of how many people suffer
from a particular ailment.
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So for example,
the morbidity rate of depression
is the rate of people who are
diagnosed with depression.
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Prevalence is a
measure that's often used
to determine the level of
morbidity in a population.
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And as we saw earlier,
it's presented in
people per 100,000.
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A person can have several
morbidities simultaneously.
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These are what we
call comorbidities.
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Morbidity statistics are
important to public health nursing.
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They measure the extent
of the nation's health.
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These data help in the
investigation of patterns of illness,
and can point public
health nurses to populations
who are most in
need of intervention.
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Okay, let's move
on to mortality.
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What is mortality?
Mortality is simply
another term for death.
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And mortality rate is
the number of deaths
due to a disease in
the total population.
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This is a measure that's also
presented in people per 100,000.
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For public health nurses,
mortality statistics
are often used
as the foundation
for formulating plans
and policies that prevent or
reduce premature mortality,
an aim to improve the
quality of life for populations.
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Now let's take a look
at some calculations.
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Let's say that
there are 25 deaths
related to a specific disease
in a population of 30,000.
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Those 25 deaths
become the numerator,
and the total population of
30,000 becomes the denominator.
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Based on this, the mortality
rate for that population
would be 83 per 100,000 people.
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Mortality varies based on the
social determinants of health.
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This means that two people
with the same illness
or the same morbidity
may have very
different outcomes.
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If one person is
economically stable,
and able to pay for treatment,
this will positively
impact their outcomes.
09:40
In fact, two people who
have the same access to care
may still have different outcomes based
on their social determinants of health.
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Social determinants of health
such as the built environment
or their community support.
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As public health nurses,
we often examine different groups
of people within the population.
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We do this to
expose vulnerabilities
based on the social
determinants of health.
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This allows us to identify
groups who would benefit most
from public health
interventions.
10:08
And doing so, we work
to decrease early mortality
and decrease health disparities.
10:14
So let's go back
to our sink analogy.
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We have our incidence
and our prevalence.
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Mortality is represented here
by water dripping out of the sink.
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So those who died due to illness
are no longer counted in our
incidence and in our prevalence.
10:30
Now let's use our sink analogy
to examine the relationship
between incidence
prevalence and mortality.
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Remember the story I
shared earlier about HIV.
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And that case,
incidence decreased.
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This means that the number
of new cases decreased.
10:45
If we look at our sink,
what we would see is that
flow of water from the faucet
would slow down,
it go down to a slow drip.
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Because mortality
also decreased.
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This means we would lose less
water from the drain in the sink.
11:00
With those two things combined,
the overall amount
of water in the sink
would actually increase the
prevalence would increase.
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And this happens because
incidence is greater than mortality
in this instance.
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Okay, and finally,
one last term.
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Disability adjusted life years.
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This is a measure
that's often used
to summarize the health
of an entire population.
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One disability
adjusted life year
represents one year
of lost healthy life.
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This statistic is
used to estimate
the gap between the
actual health of a population
and the ideal scenario in
which everyone in the population
would live well into
old age with full health.
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Disability adjusted life years
include the potential years of
life loss due to premature death,
and years of healthy life lost
due to being in poor health.
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And this sense this statistic
combines morbidity and mortality
into one single metric.
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Well, epidemiology
can be complex,
it doesn't need to
be overcomplicated.
12:04
I hope this introduction gave
you some foundational knowledge
that will help you navigate
and better understand statistics
that are often used in
public health nursing.