Chronic respiratory infection Flashcards
Learning outcomes
- Outline the range of chronic infections that can occur in the respiratory tract
- Identify patient risk factors for chronic respiratory tract infection
- Describe how antimicrobial resistance can arise in chronic respiratory tract infections
- Demonstrate an understanding of patient specific factors that need to be considered when choosing an antimicrobial which may influence the choice of antimicrobial (i.e. know colonisation with resistant organisms)
- Describe broad spectrum and narrow spectrum antimicrobials and the contribution of broad-spectrum antimicrobials to antimicrobial resistance
Tuberculosis
•Tuberculosis: granuloma formation in lungs as primary infection
a person will be infected with Mycobacterium tuberculosis in their lungs and there will be a reactive lymphadenopathy in the local lymph nodes draining the lungs. TB organisms are phagocytosed incompletely by macrophages, other macrophages then attack these and lymphocytes surround those macrophages. This generates a pathological process known as a granuloma.
•Latent TB affecting one quarter of the worlds people
•Cell-mediated immunity contains the infection
•Mycobacterium tuberculosis slow growing with a lipid rich cell wall
•TB resistance a global public health emergency
Cystic fibrosis
•CF the commonest autosomal recessive inherited condition in UK
•Chlorine channel transport abnormality leading to viscous mucoid secretions
•Step-wise alternations in respiratory organisms
•Strep pneumoand H. Influenzae
•Staph aureus
•Pseudomonas aeruginosa
The genetic lesion of cystic fibrosis leads to an increased viscosity of mucosal secretions across many epithelia in the body. In the lungs this leads to the accumulation of the secretions for which the patient has regular physiotherapy. In addition the thick secretions seen in CF are an excellent, nutritious substrate for the growth of many bacteria
Bronchiectasis
•Bronchiectasis: primary infection and inflammatory response
•Long term loss of lung architecture
•Widened airways with more secretions pooling
•Step-wise colonisation with unusual organisms
•People with CF and Bronchiectasis can be colonised with non-tuberculous mycobacteria
Bronchiectasis is a disease where there is loss of the normal lung architecture. This generally results from an infective insult, and the inflammatory response to that. The end result is widening of the airways, a loss of gas-exchange surface area and a pre-disposition to further respiratory infections.
The pathology of bronchiectasis means that patients with this condition are susceptible to recurrent respiratory tract infections
Risk factors for common RTI’s
- Chronic Obstructive Pulmonary Disease
- Cigarette smokers
- Also occupational dusts like coal
- Air pollution
- Chronic allergens
- Repeated exacerbations, especially in the winter
- Viruses, bacteria and non-infective exacerbations
- Altered epithelia and microbiome
- Aerobic gram negatives
How antimicrobial resistance can arise in chronic RTIs
- Tissue damage/ metaplasia of the epithelium
- Loss of columnar pseudostratified epithelium and muco-ciliary escalator
- Possible ‘squamous’ transformation
- Alterations in microbiome
- And loss of microbial clearance
How antimicrobial resistance can arise in chronic RTIs- contd
- Antibiotics represent a hostile environment for bacteria
- Bacteria genetically prepared to adapt to hostile environments
- Point mutations during replication can be enough to develop a resistant strain
- Promiscuous horizontal sharing of genetic material- elements like plasmids
- Resistance an inevitable result of antibiotics
How antimicrobial resistance can arise in chronic RTI’s
•Chronic conditions lead to more healthcare ‘exposures’
•Exposure to healthcare settings = exposure to more resistant bacteria
•Hospitals – the place where we cram all the sick people together
•Dependency, exposure to antibiotics, staff contacts facilitate bacterial sharing
•Infection prevention and control limits transmission of resistant strains
Patients who have to spend a lot of time in contact with healthcare workers or health care institutions will therefore tend to be exposed more resistant strains of bacteria
Patient specific factors that must be considered when choosing an antimicrobial
Firstly: is this really an infection? The history and examination are central
Secondly: what is causing this infection? Our microbiology knowledge help us here, and our ability to choose and interpret tests
Empirical or best guess treatments started pending investigation results
Review, amend or stop treatment after observing patient progress and understanding test results.
Patient specific factors that must be considered when choosing an antimicrobial- contd
- Previous results may be relevant in patients with chronic conditions
- Antimicrobial sensitivity results typically take 48 hours
- Empirical treatment takes account of the most recent previous results, or the pattern of previous results
- Treatment gets amended with the results from the current episode.
- In some patients we may ‘screen’ for some particular resistant organisms – prior healthcare, transfers, outbreaks
- The presence of these resistant strains will change our prescribing decisions
- Screening should be with sensitive tests•Low false negative rate
- A negative test has confidently excluded the condition
- Sample the part of the body most likely to have the bacteria•Nose and groin for MRSA
Describe Broad Spectrum and Narrow Spectrum Antimicrobials and the Contribution of Broad-spectrum Antimicrobials to Antimicrobial Resistance
- Broad spectrum cover = wide variety of medically important bacteria killed
- Advantage: most potential pathogens are covered and killed
- Disadvantage: broad spectrum agents usually leads to broad spectrum resistance
- Infection doctor balances risks and benefits
- Antibiotic stewardship:•’an organisational or healthcare-system-wide approach to promoting and monitoring judicious use of antimicrobials to preserve their future effectiveness
Gram staining and antibiotics
See lecture 55 for flow diagrams
