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.
Medical-Surgical Nursing - Flashcards
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.