Med-Surg Immune System, part 3: Immune System Malfunction & Infection

by Cathy Parkes September 28, 2020

In this article, we give you a basic breakdown on what happens when things go wrong in the immune system — malfunction and infection.

In immune system malfunction we cover hypersensitivity, autoimmune reactions, and immunodeficiency.

For infections, we cover the chain of infection, the stages of infection, infection risk factors, and systemic vs. local infections.

You need to know these basics to understand your Med-Surg and Critical Care topics in the immune system! These topics are covered in our Medical-Surgical Flashcards (Immune system), and Cathy’s video follows along with the cards.

Immune system malfunction

Hypersensitivity

Hypersensitivity of the immune system occurs when the immune system has an exaggerated or inappropriate response to exposure to an antigen or allergen. Your immune system seeks to destroy that antigen or allergen, and goes overboard, which results in destruction of healthy body tissue in addition to the harmful cells.

Autoimmune reaction

An autoimmune reaction is easy to understand if you break down the word into its parts. Auto means self, and immune is obvious. In an autoimmune reaction, the body’s natural defenses recognize self cells as non-self cells and target them for destruction. An autoimmune reaction can be caused by genetic, hormonal, or environmental factors.

In this playlist, we cover multiple autoimmune diseases, including Systemic Lupus Erythematosus (SLE or just “lupus”), which is a chronic inflammatory disorder of the connective tissue.

Immunodeficiency

Immunodeficiency means an immune system that is deficient; the immune response is absent or depressed. This can occur due to an infection, medication, or genetic disorder. When a patient’s immune system is not functioning at full capacity, it places them at high risk for infections.

In this playlist, a major immunodeficiency disorder we cover is HIV/AIDs, which is a virus that attacks the body’s helper T cells.

Infection

Chain of infection

Causative agent

In the chain of infection, a causative agent is the agent that is causing harm, whether that is a bacteria (e.g., food poisoning), virus (e.g., Covid-19), or some kind of toxin (e.g., snake venom).

Reservoir

Within the chain of infection, a causative agent resides in a reservoir, which can be the human body, but it could also be the soil or a pond. This is the causative agent’s usual home.

Portal of exit

Within the chain of infection, the causative agent leaves the reservoir through the portal of exit, which could be through somewhere like the respiratory tract or the blood.

Mode of transmission

In the chain of infection, once the causative agent has exited the reservoir, it needs a mode of transmission, which is how it travels. The causative agent can be transmitted through droplets, contact, or airborne.

Social distancing to slow the spread of coronavirus is an example of an attempt to stop transmission. When people are not around one another, Covid-19’s modes of transmission fail. If someone sneezes inside their house, and you are inside your house across town, their droplets can’t get to you. However, if they sneeze and you guys are sitting in the same room, their droplets have very easy access to you.

Portal of entry

In the chain of infection, portals of entry are similar to portals of exit, and can include mucous membranes, open wounds, and the respiratory tract. You can think of these portals as exit and entry doors.

Susceptible host

Next in the chain of infection, the causative agent enters through the portal of entry into a susceptible host. A susceptible host is any person at risk of infection.

Stages of infection

Incubation period

The first stage of infection is the incubation period, where the pathogen enters the body and starts to multiply. There are almost always no symptoms during this incubation period.

Prodromal stage

In the prodromal stage of infection, the pathogen continues to multiply, and the host will see the onset of general symptoms. General symptoms are usually malaise, maybe fever, just not feeling well — you know something is off with your body.

Illness stage

In the illness stage of infection, you will see onset of specific symptoms related to that particular infection. For example, in the illness stage of a respiratory infection, you would start to see runny nose and coughing.

Convalescence stage

In the convalescence stage of infection, symptoms subside and eventually disappear, and you have gradual recovery from your illness.

Risk factors

Risk factors that place an individual at higher risk for infection include:

  • Compromised immunity or disease (chronic or acute). For example, if a patient has a chronic illness like diabetes, they are definitely at a higher risk for infection.
  • Poor hygiene or sanitation
  • Crowded living environments. For example, a college dorm. If you are followed along with the chain of infection above, you know this is because you can’t prevent the causative agent’s mode of transmission from getting to other people. A crowded living environment is the opposite of social distancing.
  • IV drug use
  • Unprotected sex
  • Impaired skin integrity

Systemic vs. local infections

A patient with a systemic infection will have symptoms such as fever, malaise, chills, fatigue, tachypnea, and tachycardia.

In a patient with a local infection, which means an infection on one part of the body (e.g., an infected toe), symptoms will include edema, pain, erythema (redness), decreased function of that body part (e.g., can’t bend the toe), and warmth.

Exam Tip

On an exam, you might be asked about which patient to prioritize, a patient with a systemic infection vs. a patient with a local infection. You might be able to guess this, but you should always prioritize the systemic infection patient first! Systemic infections by definition are spread throughout the body, and have the possibility to affect organ functions like the brain, heart and lungs, and are therefore more acutely dangerous to the patient.


Full Transcript

In this video, we are going to talk about immune system malfunction as well as infection. If you're following along with cards, I'm on card number seven. Let's talk about the three main ways your immune system may malfunction.

One is something called hypersensitivity. This is where your immune system has an exaggerated or inappropriate response upon exposure to an antigen or allergen. So basically, your immune system is going after that antigen or allergen, and it kind of goes overboard, and it ends up causing inflammation or destruction of healthy body tissue as well.

Then we have an autoimmune reaction. This is where the body's normal defenses recognize self cells as non-self cells and target them. This may be due to genetic, hormonal, or environmental factors.

Then we have something called immunodeficiency. This is where we have an absent or depressed immune response. It could be due to an infection, medications, or genetic disorders. But basically, when the patient's immune system is not functioning at full capacity, it places them at high risk for infections.

Speaking of infection, let's talk about the chain of infection as well as the stages of infection.

So we have a causative agent. So that could be a bacteria, a virus, or some kind of toxin.

It resides in a reservoir, and that might be the human body, but it could also be something like the soil.

Then it leaves through the portal of exit, so that could be through the respiratory tract, or something like the blood.

It has a mode of transmission, so it may be transmitted through droplets, contact, or airborne.

And then it enters through the portal of entry into a susceptible host. So that's basically the chain of infection.

In term of the stages of infection, there are four stages.

The first stage is the incubation period. This is where the pathogen enters the body and starts to multiply. There are no symptoms during this incubation period.

Then we have the prodromal stage. This is where the pathogen continues to multiply, and we have the onset of general symptoms. So this may be like malaise, maybe fever, just generally not feeling very well.

Then we move into the illness stage. This is where we have the onset of specific symptoms related to that particular infection. So if it was a respiratory infection, now I'm getting the runny nose and the coughing, etc.

Then we have the convalescence phase this is where symptoms subside and eventually disappear, and you have gradual recovery from your illness.

Let's now touch on the risk factors that place an individual at higher risk for infection. These include compromised immunity, chronic or acute disease.

So, for example, if the patient has diabetes, that is a chronic illness, and it definitely places that patient at higher risk for infection.

We also have poor hygiene, poor sanitation, and crowded living environments.

So, for example, dormitories. I sent my daughter to the dorm last fall, and she had two roommates, plus a super crowded dorm. And she got so sick the first couple weeks of school because her immune system is basically just overwhelmed with all those other people and all of those germs. After the first couple weeks, her immune system kind of caught up and got a little tougher, and she's been healthy since. But those first couple weeks were kind of brutal.

Other risk factors associated with infection include IV drug use as well as unprotected sex and impaired skin integrity.

Then the last thing I want to go over here are the differences in symptoms between a systemic infection and a local infection.

So a patient with a systemic infection will have symptoms such as fever, malaise, chills, fatigue, tachypnea, and tachycardia.

If we are talking about a local infection, so just an infection on one part of the body, then symptoms will include edema, pain, erythema, which is a fancy name for redness, decreased function, and warmth in a particular area of the body.

So as you are answering exam questions and need to prioritize a patient, if you have one patient who has signs and symptoms of a systemic infection and another patient who has signs and symptoms of a local infection, you always want to prioritize your systemic infection patient first.

Okay. So hopefully, this video has been helpful. When I come back, we will talk about diagnostic tests that relate to the immune system and how to determine if a patient is fighting an infection, if they have inflammation in the body, that type of thing. So stay tuned, and I'll see you soon!


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