Flashcards in Infection Deck (188)
Which infection can only occur alongside HBV? In what ways? What is different about the two ways of dual infection?
Coinfection - severe acute disease with low risk of chronic
Superinfection - reactivation of HBV with high risk of chronic
Why does HDV need HBV?
HDV uses envelope of HBV
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
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
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
How do biofilms aid bacteria?
Protection from immune system
Protection from abx
Chemically favourable environment
What are the clinical problems regarding biofilms?
Poor abx penetration
Hard to grow as must shake loose first
Define hypersensitivity reactions
Inappropriate or excessive
Harm the host
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
What is the prevalence of allergy?
What is the most common?
How common is it?
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
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
How can a diagnosis of allergy be made?
Skin prick testing
Blood test for allergen specific IgE
What controls are used in skin prick testing?
Where does it test for reaction
Heparin and saline
What are the signs of epidermal allergy, dermis allergy?
Management of allergy
Education to recognise and get help
Emergency anaphylaxis tx.
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
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
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
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
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
What are problems with antibiotic resistance generally?
Resistance is irreversible
Development has stalled
Use causes resistance even if appropriate
What are the problems with abx resistance?
More severe treatments required
More expensive treatments required
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
What is the aim of abx stewardship?
Improve appropriate abx use
Achieve optimal clinical outcome
What clinicians are involved in ABX stewardship?
Infectious diseases physician
Infection control nurse
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
What type of abx stewardship intervention is most efficacious?
Initially restrictive but after several months both restrictive and persuasive
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!)