Flashcards in Infections in the Immunocompromised Host Deck (21):
What is the definition of the immunocompromised host?
Disruption of specific defence of an organ/system. Humoral/cellular.
What are the common features of infections in the immunocompromised?
- Can often predict the infection if you know the underlying disease and immune deficit
- Often organsims of low pathogenicity/opportunistic infections
What innate defences may be disrupted?
- Skin (barrier, sebum, normal flora) – iv or urinary catheters, surgery and burns
- Interferons, complement, lysozyme, acute phase proteins
- Mucous membranes (tears, urine flow, phagocytes)
- E.g. Lungs – goblet cells, muco-ciliary escalator. Cystic fibrosis
- Normal commensal flora in gut – antibiotic treatment alters flora e.g. C. difficile, Candida spp.
How are immunodeficiencies classified?
- Congenital or primary
- Acquired or secondary
Which cell presents the 2nd line of defence?
- Neutrophils (NE) very important after initial breach of innate defences
- Less NE – increasing infection
What are the possible neutrophil defects that may be present?
- Qualitative defects (e.g. lose ability to kill or chemotaxis) or
- Quantitative defects (less present)
What are the features of qualitative neutrophil defects?
– Chemotaxis – rare, congenital, inadequate signalling, abnormality in receptors or NE movement
–Killing power - inherited, Chronic Granulomatous Disease. NE fail to mount a respiratory burst in phagocytosis. Deficient in NADPH oxidase so hydrogen peroxide not formed. At risk of Staph. aureus infections
What are the features of quantitative neutrophil defects?
eg - cancer treatment, bone marrow malignancy, aplastic anaemia caused by drugs
Esp. imp. when 50% will develop an infection. Highly lethal if not treated quickly with correct antibiotics – empirical therapy, >50% those with Pseudomonal infections will die in 24hrs if not treated
What sort of infections might you see in neutropenic patients?
- Bacterial infections – Gram negative bacilli (e.g E. coli), Gram positive cocci (e.g. S. aureus ) - often normal flora. E.g. Coagulase negative staph
- Fungal infections – Candida spp. , Aspergillus spp.
What treatment is given for infections in neutropenic patients?
Broad spectrum. An aminoglycoside and an antipseudomonal penicillin, 2nd line treatment e.g. a carbapenem, then antifungals, remember viruses
What are the potential T cell deficiencies?
- Congenital – rare
- Acquired – drugs e.g. ciclosporin after transplantation (decreases graft versus host disease and rejection), steroids
- Acquired – viruses e.g. HIV
What kind of infections might you see in patients who are T cell deficient?
- May be intracellular
- BACTERIAL – Listeria monocytogenes (food), mycocteria – MTB, MAI
- VIRAL – e.g. leukaemia and transplanted pnts - HSV, CMV (pre–emptive treatment), VZV. Serological testing, prophylaxis and treatment with e.g. aciclovir and ganciclovir
- FUNGAL – e.g. Candida spp., Cryptococcus spp.
- PARASITIC - Cryptosporidium, symptomatic treatment only. Toxoplasma. Strongyloides - may get gram -ve sepsis as larvae move.
What are hypogammaglobulinaemias?
- Antibody problems
- Congenital - rare
- Acquired – multiple myeloma, chronic lymphocytic leukaemia, burns
What sort of infections do you see in patients with hypogammaglobulinaemias?
Usually encapsulated bacteria e.g. S. pneumoniae in the resp. tract or e.g. Giardia lamblia or Cryptosporidium in GIT
What kind of infections would you see in complement deficiency?
- Encapsulated bacteria. Need complement to help kill organisms. Earlier defect in pathway then greater no. of organisms may infect.
- Classical and Alternative
- e.g. C5-8 then Neisseria meningitidis is important – lysis not achieved via membrane attack complex as MAC not formed. 50-60% pnts will have 1 episode of disease in life
- Frequent, serious S. pneumoniae infections as poor quality opsonisation
- Hereditary and very rare
What are the potential consequences of a splenectomy?
- Spleen - source of complement and antibody producing B-cells, removes opsonised bacteria from blood.
- Streptococcus pneumoniae, Haemophilus influenzae type B, N. meningitidis, malaria
- High mortality, vaccination, prophylactic penicillin, education – seek help if unwell
What are biologics?
- Antibodies or other peptides
- Inhibit inflammatory cytokine signals e.g.tumour necrosis factor or TNF, inhibiting T-cell activation, or depleting B-cells.
What are the immunological risks of biologics?
Risk of tuberculosis, herpes zoster, Legionella pneumophila, and Listeria monocytogenes.
What are the consequences of organ transplantation?
Anti-rejection treatment suppresses cell mediated immunity to stop effects of cytotoxic and natural killer cells. Degree of immunosuppression varies on how closely the donor and recipient are matched.
What infections are possible in organ transplantation?
1. The initial disease (e.g. HBV, liver transplant)
2. Surgery and hospital admission (e.g. ventilator acquired pneumonia, S. aureus wound infection)
3. Organ receipt (e.g. Toxoplasmosis, CMV), patient matching
4. Opportunistic infection during initial immunosuppression (initial 3/12, e.g. CMV, Aspergillus)
5. Later opportunistic infection (after 3/12, e.g. Zoster, Listeria)