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Flashcards in Infection Deck (188)
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120

Which infection can only occur alongside HBV? In what ways? What is different about the two ways of dual infection?

HDV
Coinfection - severe acute disease with low risk of chronic
Superinfection - reactivation of HBV with high risk of chronic

121

Why does HDV need HBV?

HDV uses envelope of HBV

122

In what ways can pathogens infect the internal surface of the body or prothesis?
Examples of each

Migration - Escherichia coli - UTI
Invasion - Streptococcus pyogenes - necrotising fasciitis
Haematogenous - streptococcus viridans - infective endocarditis
Innoculation - coag -ve staphylococcus - prothesis infection

123

What are the varying causes of infective endocarditis in native and prosthetic valves?

Native and >1 yr prosthetics - Strep. viridans, Staph. aureus, Candida
<1 yr prosthetics - coag -ve staphylococcus

124

What are the stages involved in the infection of a prothetic joint? How are bacteria adapted for this?

Adherence - pili/fimbriae
Biofilm formation - ecf production, quorum sensing (signalling for neighbours to produce ecf)
Invasion and multiplication

125

How do biofilms aid bacteria?

Protection from immune system
Protection from abx
Nutrients
Chemically favourable environment

126

What are the clinical problems regarding biofilms?

Poor abx penetration
Hard to grow as must shake loose first

127

Define hypersensitivity reactions

Antigen specific
Immune response
Inappropriate or excessive
Harm the host

128

What are the four types of hypersensitivity reaction?

Type 1 - antigen interacts with IgE on MAST cells triggering mediators inc. histamine release
Type 2 - drug attaches to cell membrane of RBC becoming a hapten then bound by antibodies activating complement causing cell lysis
Type 3 - antibody antigen complex not removed from blood by phagocytosis so keeps activating complement causing endothelial damage - can be especially bad if trapped in endothelium
Type 4 - activation t cells by hapten protein complex, causes skin inflammation and rash

129

What is the prevalence of allergy?
What is the most common?
How common is it?

About 50%
Peanut
1:50

130

What is the hygiene hypothesis?

Low pathogen exposure (clean living, small family, increased abx, low dirt)
Favours increased th2 cd4 t cells which instigate second phase of an allergic reaction

131

What do mast cells release? What do they do?

Histamine - smooth muscle dilation (arterioles) and constriction (bronchioles)
Cytokines - stimulate CD4 TH2, promote eosinophils and inflammation
Chemokines - attract inflammatory cells
Leukotrines - increase vascular permeability

132

How can a diagnosis of allergy be made?

Skin prick testing
Blood test for allergen specific IgE
Allergy challenge

133

What controls are used in skin prick testing?
Where does it test for reaction

Heparin and saline
Epidermis

134

What are the signs of epidermal allergy, dermis allergy?

Urticaria
Angioedema

135

Management of allergy

Allergen avoidance!
Education to recognise and get help
Epipen
Medialert
Desensitisation therapy
Emergency anaphylaxis tx.

136

What levels of disease can transmissable infection cause?

Endemic disease - normal background rate
Outbreak - 2 or more cases linked in time and place
Epidemic - a rate of infection greater that background rate
Pandemic - very high rate of infection across many countries and continents

137

How can we classify if a disease is going to increase in cases, remain constant or decrease in cases?

R0 number - the number of people one case infects
If more than 1 then numbers will increase
If 1 numbers will be constant
If less than 1 numbers will decrease

138

What could lead to an new increase in number of infections?

New pathogens - e.g. Mutation, spread
New person - e.g. Migration, newborn baby
New practice - e.g. Air conditioning

139

How do the general pattern of cases in epidemics and outbreaks differ?

Epidemics tend to follow a bell curve distribution of incidence against time
Outbreaks tend to follow a much more random distribution - they can be large with excellent control or small with non. This can lead to the false belief a certain intervention is effective even when it isn't

140

What is a paradox in polio control regarding immunisation? How can this paradox be applied to a western disease?

Those not immunised are exposed later in life and thus experience more severe disease (increased paralysis)
More adult chickenpox and thus increased infertility

141

What are problems with antibiotic resistance generally?

Resistance is irreversible
Development has stalled
Use causes resistance even if appropriate

142

What are the problems with abx resistance?

Treatment failure
More severe treatments required
More expensive treatments required
Prophylaxis failure

143

What are the different classifications of resistance to abx?

Resistant - 1 or more agents in 1or 2 classes
Multi drug (MDR) - 1 or more agents in 3 or more classes
Extensively drug (XDR) - more than 1 agent in all but 2 classes
Pan drug (PDR) - all agents in all classes

144

What is the aim of abx stewardship?

Improve appropriate abx use
Achieve optimal clinical outcome
Minimise toxicity
Reduce cost
Limit resistance

145

What clinicians are involved in ABX stewardship?

Medical microbiologist
Infectious diseases physician
Antimicrobial pharmacist
Infection control nurse
Hospital epidemiologist

146

What types of intervention are there for antimicrobial stewardship?

Persuasive - education, consensus between clinicians, reminders, audits, feedback
Restrictive - limit abx on susceptability report, restrict formulary, require authorisation,
Structural - rapid lab tests to avoid general administration, computerised records

147

What type of abx stewardship intervention is most efficacious?

Initially restrictive but after several months both restrictive and persuasive

148

What are the outcomes seen from abx stewardship?

Non significant reduction in death rate
Significant reduction in length of stay
Significant increase in readmission (why!)

149

What is the pattern of infection seen in CF patients?

Birth - 3m = haemophillus influenzae
3m - 3y = staphylococcus aureus
3y - teens = pseudomonas aeruginosa
teens - 30s = atypical mycobacteria, candida, aspergillus