Infections of Immunocompromised host Flashcards
What is primary immunodeficiency?
Inherited (so quite rare)
- due to exposure in utero to environmental factors
What is secondary immunodeficiency?
An underlying disease state or treatment for a disease that inhibits/wipes out part of the immune system
- common
Why are numbers of immunocompromised patients increasing?
Improved survival at the extremes of life
Improved cancer treatment
Developments in transplant techniques
Developments in intensive care
Management of chronic inflammatory conditions
- immunomodulatory agents including steriods
What is the most common cause of morbidity and mortality in the immunocompromised host?
Infections - a specific deficiency increases susceptibility to pathogens normally eradicated by that defense mechanism
A specific deficiency increases susceptibility to pathogens
normally eradicated by that defense mechanism, but why is it not always that straightforward?
Basic patterns are recognisable, but organisms are unpredictable
Isolated deficiencies are rare as there is a complex interplay of pathways
- malfunction of one part often influences another
Underlying diseases and their treatment affect a range of mechanisms
Which parts of the immune system do cytotoxic drugs, irradiation and steroids affect?
Neutrophil function
- Chemotaxis
- Phagocytic activity
- Intracellular killing
If netrophil function is affected, which pathogens are most likely to infect a patient?
Gram positive cocci - staph aureus - coagulase negative staph - viridans strep - enterococci Anaerobes - bacteriodes - clostridia Gram negative bacilli - E.coli - pseudomonas aeruginosa - klebisella pneumoniae - enterobacter Fungi - cadida - aspergillus
Describe chronic granulomatous disease.
An X-linked inherited disorder (most common inherited)
Defect in gene coding for NADPH oxidase
- deficient production of oxygen radicals
- defective intracellular killing
Recurrent bacterial and fungal infections
- abscesses in the lungs, lymph nodes and skin
- inflammatory responses; widespread granuloma formation
What are the most common pulmonary infections in chronic granulomatous disease?
Aspergillus
Staph aureus
Nocardia
What conditions/drugs suppress cellular immunity?
DiGeorge syndrome - failure of T-cell proliferation
Malignant lymphoma
Cytotoxic chemotherapy
Extensive irradiation
Immunosuppressive drugs
Allogenic stem cell transplantation, especially in GvHD
- because of high dose steriod treatment
Infections - HIV, mycobacterial infections, measles, EBV and CMV
Which kinds of immunosuppresive drugs cause suppression of cellular immunity?
Corticosteriods
Cyclosporin - immunosuppressant used to prevent organ rejection
Tacrolimus - more potent than cyclosporin
Alemtuzumab - anti-CD52 monoclonal
Rituximab - anti-CD20 monoclonal used in rheumatoid arthritis
Purine analogues (fludarabine) - causes profound lymphopaenia used in cytotoxic chemotherapy
What are some causes of humoral immunity suppression?
Bruton agammaglobinaemia (primary, rare) Lymphoproliferative disorders cause decreased antibody production - CLL, multiple myeloma - preserved in acute leukemia Intensive radio/chemotherapy
What happens if someone doesn’t have a spleen, or it is under active?
Splenic macrophages eliminate non-opsonised microbes (encapsulated bacteria) with a specific opsonising antibody required for phagocytosis of encapsulated bacteria
- lack of this impairs activity of all phagocytic cells
What bacteria/viruses are most likely to affect someone with humoral deficiency, splenectomy or hyposplenism?
Strep pneumoniae
Haemophilus influenzae type B
Neisseria meningitidis
What are the physical barriers against microbial invasion?
Skin Conjunctivae Mucous membranes - gut - respiratory tract - GU tract
How do we protect out mucosal surfaces from colonisation?
Colonisation resistance occurs due to our normal flora
- they coat our mucous surfaces and stop colonisation of pathogenic organisms (e.g. C.diff)
How is our skin effective at preventing pathogenic invasion?
Desquamates - high turnover physically removes organisms from the skin surface
Dry
Slightly acidic pH
Temperature 5C cooler than the body, so the organisms can’t live
Secretory IgA in sweat
What impairs the integrity of the skin?
Chemotherapy/irradiation Cuts Abrasions Sclerosis Burns Surgical incisions - cellulitis common Lines/needles
Why are lines and needles important methods of infection in an immunocompromised host in a hospital environment?
Hickman lines - chemotherapy administration
Venflons
- used and wiggled too often
- organisms can travel up the venflon or sit in the port and wait for it to be opened
- S.aureus
- cellulitis due to disseminated S.aureus
How can organisms be introduced into the body and enter through mucosal surfaces?
Ventialtion - direct lines of access into respiratory tract
How can chemotherapy and irradiation impair the integrity of the GI tract?
High mitotic index and inflammatory response in the lymphoid tissue.
This causes mucositis -> pain, dysphagia, xerostomia and ulceration
- if the pH is affected, the organisms may be able to survive the stomach
This impairs GI function and its permeability
Nutritional status is altered
How does impaired nutritional status cause immunodeficiency?
Compromise integrity of the host defences
- Anorexia
- Nausea and vomiting
- Mucositis
- Metabolic derangements
Iron deficiency reduces microbial capacity of neutrophils and T-cell function
What is the clinical definition of severe nutritional deficiency?
less than 75% ideal body weight
or
rapid weight loss and hypoalbuminaemia
How can organ dysfunction lead to increased susceptibility for infection
Obstruction - build up of secretions increases susceptibility
CNS tumors/spinal cord compression
- loss of cough/swallow reflex
- incomplete bladder emptying
Diabetes mellitus - reduced opsonisation, chemotaxis
Stress - reduced T-cell function
