Introduction to Epidemiology (Nursing)

by Heide Cygan, DNP, RN

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    00:01 This is an introduction to epidemiology.

    00:06 Epidemiology is a word that we hear often in nursing.

    00:09 But we don't always know what it means.

    00:11 And because we don't know what it means, it can be a little bit scary.

    00:15 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.

    00:26 So let's first break it down into three parts.

    00:31 Epi simply means being above.

    00:34 Demi, that's our population.

    00:38 Ology is the study of.

    00:42 So when we bring it all together, epidemiology is studying that which is above what is expected in the population.

    00:51 Epidemiology is used to find the causes of health outcomes and diseases in our population.

    00:57 In epidemiology, the public health nurse sees the patient as the community as the population.

    01:04 This means that individuals are viewed collectively as an aggregate.

    01:08 So let's take a look at some common terms that are important in epidemiology.

    01:13 Let's start with incidence.

    01:15 Incidence is the number of new cases of a disease within a population over a specific period of time.

    01:23 It's the number of newly diagnosed cases of a disease.

    01:26 So for looking at the incidence of a disease this year, we're looking at the number of new cases this year.

    01:34 Incidence is a measure that allows us to determine an individual's probability of being diagnosed with the disease during a specific timeframe.

    01:44 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.

    01:55 So let's say we're using epidemiology to explore a specific type of cancer.

    02:00 We know that over the course of one year, three people have been diagnosed with this specific type of cancer.

    02:07 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.

    02:18 We use the three who are newly diagnosed as the numerator, and the 200 of total population as the denominator.

    02:26 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.

    02:41 To better explain this, imagine a sink.

    02:45 The fresh water flowing from the faucet and remaining in the sink represents the new cases of disease this year.

    02:52 This is the incidence.

    02:53 Now remember this example because we're going to come back to it.

    02:58 Okay, let's move on and talk about another important term.

    03:02 Prevalence.

    03:03 Prevalence is the number of existing cases of a disease in a population at any given point in time.

    03:10 This would mean examining a specific disease and learning how many cases exist in the population today.

    03:17 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.

    03:26 Prevalence rate is the total number of cases of disease existing in the population divided by the total number in the population.

    03:36 So let's continue on with our example that we use for incidents.

    03:41 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.

    03:50 Now let's imagine that prior to that time period, two people were living with cancer.

    03:54 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.

    04:02 We use the total population or 200 as the denominator.

    04:06 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.

    04:20 So let's go back to our sink analogy.

    04:23 Here we see that there's already water standing in the bottom of the sink.

    04:27 This represents people who already have the disease.

    04:30 That water plus the fresh water pouring in from the faucet which represents the incidence, the new cases of disease.

    04:37 Combined, this is prevalence.

    04:40 Incidence and prevalence are often confused with each other, but as we just saw, they're different.

    04:46 Incidence is the proportion of individuals in a population who develop a condition during a particular time period.

    04:54 Prevalence is the proportion of individuals within a population who have a condition at any particular or a moment in time.

    05:01 So incidence includes new cases only.

    05:04 And prevalence includes new and pre existing cases.

    05:09 When we're doing our calculations, this means that the main difference between incidence and prevalence is their numerators.

    05:15 The total healthy population or the denominator remains the same.

    05:20 Okay, so let's focus for just a minute on only the numerator.

    05:24 The numerator of incidence consists only of people whose illness started or was diagnosed during that specific time period.

    05:32 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.

    05:46 So when might you use one measure over the other? Well, let's think about this for a minute.

    05:51 Prevalence is based on both incidence and duration of illness.

    05:55 A high prevalence of disease within a population might be the result of high incidence or the result of prolonged survival without a cure.

    06:04 On the other hand, low prevalence might indicate low incidence, or a disease process that's rapidly fatal, or has a rapid recovery.

    06:14 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.

    06:24 On the other hand, incidence is often used with communicable diseases such as influenza.

    06:30 Let me share an example from a colleague who worked to improve outcomes for patients diagnosed with HIV.

    06:36 She was working in the community at a time when a new and effective intervention was introduced.

    06:41 Because of this intervention, fewer cases of HIV progressed to AIDS.

    06:46 And because of that, fewer people died.

    06:49 At the same time, she was also running an effective prevention program.

    06:54 So while incidents decreased, now remember, that's the number of new cases of disease, prevalence continued to increase because fewer people were dying.

    07:03 So in fact, an increase in prevalence and a decrease in incidence showed improvement in the community's overall HIV outcomes.

    07:13 Okay, time to shift gears a little.

    07:15 Now we're going to talk about morbidity and mortality.

    07:18 What is morbidity? Morbidity is simply another term for illness.

    07:23 Examples of morbidities are heart disease, Alzheimer's disease, cancer, traumatic brain injury.

    07:30 It's important to remember that morbidity is not death.

    07:33 It's simply a measure of illness.

    07:36 When people experienced morbidity, there's a disruption in their body's ability to function.

    07:42 They may have physical deficits, infections, or mental health challenges.

    07:46 Morbidity rates are simply a measure of how many people suffer from a particular ailment.

    07:51 So for example, the morbidity rate of depression is the rate of people who are diagnosed with depression.

    07:58 Prevalence is a measure that's often used to determine the level of morbidity in a population.

    08:03 And as we saw earlier, it's presented in people per 100,000.

    08:09 A person can have several morbidities simultaneously.

    08:12 These are what we call comorbidities.

    08:15 Morbidity statistics are important to public health nursing.

    08:18 They measure the extent of the nation's health.

    08:21 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.

    08:30 Okay, let's move on to mortality.

    08:32 What is mortality? Mortality is simply another term for death.

    08:36 And mortality rate is the number of deaths due to a disease in the total population.

    08:41 This is a measure that's also presented in people per 100,000.

    08:46 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.

    09:00 Now let's take a look at some calculations.

    09:02 Let's say that there are 25 deaths related to a specific disease in a population of 30,000.

    09:10 Those 25 deaths become the numerator, and the total population of 30,000 becomes the denominator.

    09:17 Based on this, the mortality rate for that population would be 83 per 100,000 people.

    09:24 Mortality varies based on the social determinants of health.

    09:27 This means that two people with the same illness or the same morbidity may have very different outcomes.

    09:34 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.

    09:48 Social determinants of health such as the built environment or their community support.

    09:53 As public health nurses, we often examine different groups of people within the population.

    09:58 We do this to expose vulnerabilities based on the social determinants of health.

    10:03 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.

    10:17 We have our incidence and our prevalence.

    10:19 Mortality is represented here by water dripping out of the sink.

    10:24 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.

    10:36 Remember the story I shared earlier about HIV.

    10:40 And that case, incidence decreased.

    10:42 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.

    10:53 Because mortality also decreased.

    10:56 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.

    11:08 And this happens because incidence is greater than mortality in this instance.

    11:14 Okay, and finally, one last term.

    11:17 Disability adjusted life years.

    11:20 This is a measure that's often used to summarize the health of an entire population.

    11:25 One disability adjusted life year represents one year of lost healthy life.

    11:31 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.

    11:43 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.

    11:53 And this sense this statistic combines morbidity and mortality into one single metric.

    11:59 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.

    About the Lecture

    The lecture Introduction to Epidemiology (Nursing) by Heide Cygan, DNP, RN is from the course Epidemiology (Nursing).

    Included Quiz Questions

    1. The study of the incidence and distribution of health-related events in specific populations
    2. The study of changes in structure and behavior in specific populations
    3. The study of how a specific disease affects the general population
    4. The study of how different populations come into contact with different populations
    1. Divide 20 by 1500
    2. Multiply 20 by 1500
    3. Subtract 20+10 from 1500
    4. Add 20 and 10 together and divide by 1500
    1. 0.3
    2. 0.25
    3. 0.005
    4. 0.05
    1. The rate of people who are diagnosed with CHF
    2. The number of people diagnosed with CHF in the last year
    3. The rate of people who have died from CHF
    4. The number of people who have died from CHF compared to the total population
    1. Disability-adjusted life year (DALY)
    2. Incidence
    3. Prevalence
    4. Morbidity-mortality ratio

    Author of lecture Introduction to Epidemiology (Nursing)

     Heide Cygan, DNP, RN

    Heide Cygan, DNP, RN

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