Week 9 - Chronic Health and Infections

Question 1

What are the different types of chronic disease?

Answer 1

• Congenital:
• – Genetic
• – Developmental
• Acquired:
• – Vascular
• – Infective
• – Traumatic
• – Autoimmune
• – Metabolic
• – Inflammatory
• – Neurological
• – Neoplastic
• – Degenerative
• – Environmental
• – Idiopathic

Question 2

What is the link between chronic diseases and infection?

Answer 2

They can predispose to specific and characteristic infections

• They cause a change in the structure or function of affected tissues/organs
• – This may have the potential for changing the interaction between the patient and micro-organism
• May be subsequently and further affected by changes caused by the altered presence of micro-organisms and the consequences of treatment

Question 3

What is the microbiology of acute exacerbations of COPD?

Answer 3

• Bacterial (may be present due to contamination)
• – Strep pneumoniae
• – H. influenzae
• – Moraxella catarrhalis
• – Psuedomonas aeruginosa
• – E. coli
• Viral
• – Respiratory syncytial virus
• – Rhinovirus
• – Parainfluenza virus
• – Human matapneumovirus
• – Coronavirus
• – Adenovirus
• – Influenza A virus

Question 4

Describe how infections impact on Down’s Syndrome

Answer 4

• Respiratory tract infections are more common in young people with down’s syndrome
  — Viral and bacterial
  — May be due to true immunodeficiency or to other factors
  • E.g. altered mucus secretion or the structure of the mouth and airways
• An otherwise healthy person with Down’s syndrome will probably not suffer many more serious infections than his or her siblings and will respond to vaccination

Question 5

How is immunity affected in Down’s Syndrome?

Answer 5

• Humoral immunity:
  — Decreased neutrophil and monocyte function
  — Normal numbers of neutrophils and monocytes
  — Immunoglobulin levels are lowered (in infants) or raised (in adults)
  o Normal or raised levels of serum IgA and secretory IgA
  — Lowered specific antibody responses upon immunisation
  — Normal or raised levels of C3, C4 and C5
• Cellular immunity
  — Altered distribution of T cell populations, but normal T cell numbers
  — Lowered T cell function
  — Altered T cell intracellular signalling
  — Abnormal cytokine production
  — Lowering of some, but not all, NK cell functions
  — Increased numbers of NK cells

Question 6

Describe the link between cystic fibrosis and infections

Answer 6

• Defect in CFTR leads to defects in Cl- transmembrane transport
• Mucus becomes dehydrated and thick, causing blockage in small ducts
• Colonisation of organisms may be due to:
  — Lung colonisation and infection with a procession of different organisms
  — Lung damage, antibacterial and steroid treatment
• Colonisation of lungs by: (in time order)
  — Haemophilus influenzae
  — Staph aureus
  — Pseudomonas aeruginosa
  — Burkholderia cepacia
  — Atypical mycobacteria
  • E.g. mycobacterium coloniae
  — Candida albicans
  — Aspergillus fumigatus
• Try to avoid contact of CF patients with other CF patients
  — Since can pass on organisms which may be fatal to each other
• Heterozygosity of CF may provide resistance to cholera, typhoid or TB

Question 7

Describe the link between diabetes and infections

Answer 7

• Hyperglycaemia and acidaemia impair:
  — Humoral immunity
  — Polymorphonuclear leukocyte and lymphocyte functions
• Diabetic micro- and macro-vascular disease result in poor tissue perfusion and increased risk of infection
• Diabetic neuropathy causes diminished sensation resulting in unnoticed skin
• ENT infections:
  — Malignant (can cause death) or necrotizing otitis externa
  • Pseudomonas aeruginosa
  • Infections starts in the external auditory canal and spreads to adjacent soft tissue, cartilage and bone
  • Patients typically present with severe ear pain and otorrhoea
  — Rhinocerebral mucormycosis
  • In patients with poorly controlled diabetes
  • Especially those with frequent episodes of DKA
  • Mould fungi
  • Organisms colonise the nose and paranasal sinuses, spreading to adjacent tissues by invading blood vessels and causing soft tissue necrosis and bony erosion
• Urinary tract infections
  — Neurogenic bladder due to diabetic neuropathy leads to defects in bladder emptying
  — Increased risk of asymptomatic bacteriuria and pyuria, cystitis and upper UTI
  — Causative organisms: enterobacteriaceae (e.g. E coli), Ps aeruginosa
• Skin and soft tissue infection
  — Predisposing factors:
  • Sensory neuropathy
  • Atherosclerotic vascular disease (decreased size of vessels so blood flow is slowed)
  • Hyperglycaemia (acts as a nutrient to bacteria)
  — Causative organisms:
  • Staph aureus (folliculitis, cellulitis)
  • Group A β-haemolytic streptococcus (cellulitis)
  • Polymicrobial, including: staph aureus, β-haemolytic streptococci, enterobacteriaceae, various anaerobes (diabetic foot ulcers, necrotising fasciitis)

Question 8

Describe pseudomonas aeruginosa

Answer 8

• Pseudomonas aeruginosa forms a thick mucus biofilm which antibiotics generally cannot penetrate
• – It is resistant to most oral antibiotics other than ciprofloxacin
• It is very difficult for oxygen to diffuse through this mucus layer
• A gram-negative, aerobic bacilli
• An opportunistic infection