Epidemiological Frameworks: Epidemiological Triangle (Nursing)

by Heide Cygan, DNP, RN

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    00:07 Here we have George, our public health nurse.

    00:10 As a public health nurse, he uses epidemiology to understand population health outcomes.

    00:17 And to do this, he needs to understand how diseases are spread from person to person.

    00:22 The epidemiological triangle is one framework that we can use to learn how diseases are spread, and how to stop the spread of disease.

    00:30 So here we have the epidemiological triangle, or what you sometimes hear called the host agent environment model.

    00:38 And the reason we call it that sometimes is because there's three parts of this model, the host, the agent, and the environment.

    00:46 So this model helps explain who has been harmed by the disease, what causes the disease, and the conditions that allow the disease to exist.

    00:55 So let's take a look at each part of the model.

    00:59 Let's start first with the host.

    01:02 And this model, the host is the susceptible human or animal who harbors and nourishes a disease causing agent.

    01:10 So this is the person who gets sick or is harmed by an agent.

    01:14 Now, there are several factors that influence the host susceptibility to an agent.

    01:19 Susceptibility is really just our ability or inability to resist harm caused by an agent.

    01:27 And there are several factors that influence our susceptibility.

    01:31 There are physical factors such as our age, our genetics, these all influence a host vulnerability to being harmed by an agent.

    01:40 We also have psychological factors to consider.

    01:43 This could be the amount of stress that we're under and our response to that stress.

    01:48 And finally, we have lifestyle factors.

    01:51 These play a major role in our ability to resist an agent.

    01:55 Some examples could be the amount of sleep that we're getting, or the amount of physical activity or the types of food that we're eating.

    02:03 These are really are healthy or unhealthy habits.

    02:07 The concept of resistance is important for public health nurses, people, or hosts, sometimes have a natural ability to resist agents.

    02:17 This is what we call inherent resistance.

    02:20 And typically, these people or hosts have characteristics that work in their favor that allow them to resist that agent.

    02:29 So for example, people who maintain a healthful lifestyle have a higher inherent resistance.

    02:35 These are individuals who are getting more sleep who are eating more healthful foods.

    02:41 So for example, if someone who has a healthy lifestyle is comes in contact with the influenza virus, they may not get sick because they have a high inherent resistance.

    02:52 It's important for us to remember that we can promote inherent resistance through preventative interventions that support those healthy lifestyles, not just for individuals, but also for populations.

    03:04 So let's move on to the second part of the framework, the agent.

    03:08 An agent is a factor that causes or contributes to a health problem.

    03:13 This is something that causes harm make someone sick.

    03:17 Agents can cause harm by being present, such as the bacteria that causes strep throat, when it's present, you get sick.

    03:24 Agents can also be harmful because they're missing.

    03:27 So for example, a low serum iron level can cause anemia.

    03:33 Now, there are five different types of agents, biological, chemical, nutrient, physical, and psychological.

    03:41 We have an entire other video about these specific types of agents.

    03:46 So if you haven't listened to it yet as soon as you're done with this one, watch that one next.

    03:53 And finally, we have the last part of the framework, the environment.

    03:57 The environment refers to all of the external factors surrounding the host that might influence their susceptibility.

    04:05 So here we're talking about things such as climate, or weather, safety of neighborhoods, safety of buildings, the quality of water, the availability of food, the presence of vectors, there's a lot going on in the environment.

    04:19 We should also consider the psychosocial environment.

    04:22 This refers to the social, cultural and economic conditions that can affect our health.

    04:28 This could be access to health care, income level, or even stress caused by worker school.

    04:35 These can all contribute to disease susceptibility.

    04:40 Now let's take a look at the entire model once more before we walk through an example.

    04:45 On the bottom left, we have the host.

    04:48 Now remember, the host is the person or the animal who's harmed by the agent.

    04:53 On the top, that's where we see the agent.

    04:56 The agent is what causes harm.

    04:59 And then on the bottom right, we have the environment.

    05:01 The environment or simply the conditions.

    05:04 The conditions that contribute to the susceptibility of the host.

    05:08 Now imagine in the center that we have the disease, When all of the pathways between the three factors are clear disease occurs.

    05:18 However, if we can break one of those pathways, then disease will not occur.

    05:23 So for example, you could work on strategies that stop the agent from ever coming in contact with the host.

    05:30 A really great one is social distancing.

    05:35 Or maybe you focus on the susceptibility of the host, and you encourage vaccinations as a way to make the host less susceptible to harm from an agent.

    05:45 You could also focus on the environment by improving access to care for those who need it most.

    05:52 Now remember, if you disrupt the pathway between any three parts of the model, you'll prevent disease.

    06:00 So let's take a look at a case study focused on HIV.

    06:06 Here we have the host.

    06:07 This is an individual who has human immunodeficiency virus or HIV.

    06:13 Because this person carries and nourishes the disease causing agent, they're considered the host.

    06:20 Now let's think about what could impact the host susceptibility.

    06:25 We know that people with other sexually transmitted infections are more susceptible to getting HIV.

    06:32 We also know that use of pre exposure prophylactic medication can decrease susceptibility.

    06:40 Let's move on to the agent.

    06:42 HIV is a viral infection that targets an individual's immune system.

    06:48 This makes a person more vulnerable to other infections.

    06:51 So thinking back to our five different types of agent, which type of agent would this be? Now if you said biological, you're right, HIV is a virus.

    07:03 As an agent, it's transmitted through direct contact with an infected person's bodily fluids.

    07:10 Okay, finally, the environment.

    07:13 Now there are a number of environmental factors that contribute to the risk of HIV.

    07:18 Specifically, the social determinants of health play a major role here.

    07:22 For example, communities with high rates of sexually transmitted infections, but lower opportunities for screening, reporting, and treatment, allow HIV to flourish.

    07:34 Low socio economic status limits access to care and treatment.

    07:39 And sometimes fear of discrimination can really discourage individuals from being tested or seeking care.

    07:45 These are all environmental factors.

    07:48 Now remember, all we have to do in order to stop transmission is to disrupt the pathway between two points of the triangle.

    07:57 Let's take a look at just one side.

    08:00 How would you disrupt the pathway between the host and the agent? So in this case, how would you prevent the person from coming in contact with the virus? Safer sex practices, such as condom use are one way to prevent the host from coming in contact with the agent.

    08:17 Now, as a public health nurse, you could educate individuals about condom use, or you could advocate for policies that ensure condoms are available widely in the community.

    08:30 Understanding how diseases are spread is the first step in developing interventions that keep communities healthier.

    About the Lecture

    The lecture Epidemiological Frameworks: Epidemiological Triangle (Nursing) by Heide Cygan, DNP, RN is from the course Epidemiology (Nursing).

    Included Quiz Questions

    1. The agent
    2. The host
    3. The environment
    4. The impact
    5. The intervention
    1. Inherent resistance
    2. Herd immunity
    3. Innate immunity
    4. Acquired resistance
    1. Organizing a vaccine clinic.
    2. Offering free child care to working parents.
    3. Organizing a winter coat drive.
    4. Offering nutrition counseling.
    1. Environment
    2. Host
    3. Agent
    4. Intervention

    Author of lecture Epidemiological Frameworks: Epidemiological Triangle (Nursing)

     Heide Cygan, DNP, RN

    Heide Cygan, DNP, RN

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