Infection: The immunocompromised host Flashcards
What is an immunocompromised host?
A state in which the immune system is unable to respond effectively to infectious microorganisms due to a defect in one or more components of the immune system
What are primary and secondary immunodeficiencies?
Primary immunodeficiency is congenital - due to either missing protein, missing cell or non functioning components.
Secondary immunodeficiency is acquired - due to a disease or treatment leading to loss of production/function of immune components, or catabolism of immune components.
When should you suspect a pt has an underlying immunodeficiency?
Infections are SPUR:
Severe - need hospitalisation, life threatening
Persistant - fails to respond to usual treatment
Unusual - unusual site or unusual MO (opportunistic)
Recurrent
What is the number 1 warning sign for a primary immunodeficiency?
A family history of PID
What are the 3 most common primary immunodeficiencies?
- Common variable immunodeficiency (very low IgG + low IgA or IgM)
- IgA deficiency - usually asymptomatic
- IgG - usually asymptomatic
What is SCID?
Severe combined immunodeficiency - there are very few T cells causing a B cell defect (don’t produce antibodies)
What is the likely diagnosis if the pt is:
Less than 6 months
6m - 5 yrs
Over 5yrs
Onset before 6m suggest T cell or phagocyte defect
Onset between 6m and 5yrs suggests a B cell/antibody or phagocyte defect (first 6m had maternal IgG)
Onset over the age of 5 usually suggest B cell/ antibody/ complement deficiency or secondary immunodeficiency (90%)
What are some of the supportive treatments for primary immunodeficiency diseases?
Prophylactic antimicrobials
Nutritional support - vit A and D good for immune system
Avoid live attenuated vaccines in severe PIDs eg SCID
What are some of the specific treatments for primary immunodeficiency diseases?
Regular immunoglobulin theraoy
SCID: haematopoietic stem cell therapy
Give some examples of secondary immune deficiencies
Most common is malnutrition HIV Liver diseases (synthesises proteins) Splenectomy Protein losing conditions eg nephropathy, enteropathy, crohns
What is the management for asplenic pts?
Life long penicillin prophylaxis
Immunisation against encapsulated bacteria (H influenzae, strep pneumoniae, neisseria meningitidis)
Medic alert bracelets and cards
What is the immune function of the spleen?
The spleen sensed encapsulated bacteria in the blood and the produces IgM and IgG. There are splenic macrophages which remove opsonised microbes - if they aren’t opsonised then they can be removed.
What are some laboratory investigations of immunodeficiency?
- FBC
- test antibody response
- lymphocyte count
- neutrophil count
- test complement function
