Infection 7-12 Flashcards
What is a surface?
Interface between a solid and either a liquid or gas
What are common viruses on the skin?
Papilloma
Herpes simplex
What are common bacteria on teh skin?
+ Staph aureus
+ Coagulase negative staphylococci
+Corynebactrium
- Enterobacterium
What are common fungi on the skin?
Yeasts
Dermatophytes - athletes foot
What are common parasites on the skin?
mites
What are microbiota?
“Commensals”
Micro-organisms carried on skin and mucosal surfaces
Normally harmless or even beneficial
Transfer to other sites can be harmful
What parts of the body are considered to be external?
Skin GI tract Resp tract Urinary tract Make contact with external environment
What is a prosthetic surface infection?
Internal infection from external origin Eg: - IV lines - peritoneal dialysis catheters - prosthetic joints - cardiac valves - pacing wires - endovascular grafts - ventriculo-peritoneal shunts
What is native valve endocarditis?
viridans Streptococci usually common in mouth, may get into blood stream when gums bleed.
Heart valves damaged by turbulent blood flow become good site for bacteria to colonise as they have similar receptors to those in the mouth.
What bacteria may cause native valve endocarditis?
viridans Streptococci Enterococcus faecalis Staph aureus HACEK group Candida (fungi)
What bacteria commonly cause prosthetic valve endocarditis and what other diseases might they cause?
coagulase negative staphylococci
Staphylococcus aureus
May also be the cause of prosthetic joint infections or cardiac pacing wire endocarditis
What are the processes in the pathogenesis of infection at surfaces?
Adherence to host cells or prosthetic surface
Biofilm formation
Invasion and multiplication
Host response - Pyogenic (neutrophils -> pus)/Granulomatous (fibroblasts, lymphocytes, macrophages -> nodular inflammatory lesions)
What does quorum sensing control?
Sporulation
Biofilm formation
Virulence factor secretion
What are the 3 principles of quorum sensing?
Signalling molecules - autoinducers (AI)
Cell surface or cytoplasmic receptors
Gene expression - co-perative behaviours and more AI production
How do microorganisms cause disease?
Exposure Adherence Invasion Multiplication Dissemination
What are the challenges of management of a surface infection?
Adherent organisms
Low metabolic state/small colony variants
Poor antibacterial penetration into biofilm micro-organisms
Dangers/difficulties of surgery
What investigations are done to confirm the origin of infection for surface infections?
Blood cultures
Tissue/prosthetic material sonication and culture
What is the aim of treatment of a surface infection?
Sterilise tissue
Reduce bioburden
What treatment is given for a surface infection?
Antibacterials
Surgery - resect infected material
What preventative mechanisms are in place against surface infection?
Natural surface: - Maintain surface integrity - prevent bacterial surface colonisation - Remove colonising bacteria Prosthetic surfaces: - Prevent contamination - Inhibit surface colonisation - Remove colonising bacteria
What is a biofilm?
combination of the proteoglycans produced by the bacteria and the host immune response (neutrophils and platelets) that surround the bacteria.
Allows the transfer of nutrients to the bacteria and waste away, aswell as protecting the bacteria from host immune response and antibiotics.
What is catheter fever?
Transient gram negative septicaemia from catheter removal/ insertion
How can infection from IV lines be prevented?
Use silver coated lines - poor adhesion to silver therefore less likely to be infected
What type of infections may not be transferrable from person to person?
Food/water - food poisoning organisms
Environmental - Legionella pneumophila
Animals - Rabies
Name some infections which require a vector for transmission.
Malaria, dengue - mosquitos
toxoplasmosis - cats
Lyme disease, spotted fever - ticks
What is an endemic disease?
A disease which is spreading at the usual background rate
What is an outbreak of disease?
Two or more cases linked in time and place
What is an epidemic?
A rate of infection greater than the usual background rate.
What is a pandemic?
Very high rate of infection spreading across many regions, countries and continents
What is R0 in infection?
The average number of cases one case generates over the course of its infectious period in an otherwise uninfected, non-immune population
What are the reasons for new outbreaks, epidemics/pandemics?
New pathogen (antigens, virulence factors, antibacterial resistance) New hosts (non-immunes, healthcare effects) New practice can cause patient and pathogen to come into contact with each other (social, healthcare)
What is an infectious does?
Number of micro-organisms required to cause infection. Varies by micro-organism, presentation of micro-organism and immunity of potential host
What does an epidemic curve show?
Number of people infected at each time interval
Susceptible -> infected -> recovered
How can pathogens and vectors be intervened?
Reduced/eradicated:
- antibacterials including disinfectants
- decontamination
- sterilisation
- eliminate vector breeding sites
What interventions are used on patients to remove/prevent infection?
Improved health - nutrition, medical treatment
Immunity - passive eg maternal antibody, intravenous immunolglobulin. Active - vaccination
What interventions occur in practice to prevent infections?
Avoidance of pathogen and it’s vector:
- Geographic
- Protective clothing, equipment - long sleeves, trousers against mosquito bites, personal protective equipment in hospitals - gowns, gloves, masks
- Behavioural - safe sex, safe disposal of sharps, food and drink prep.
What interventions can be used in everyday life to prevent infection?
Safe water
Safe air
Good quality housing
Well designed healthcare facilities
What is herd immunity?
When vaccination of a sufficient proportion of the population provides immunity for the entire population
What are the consequences of control of disease?
Good:
- Decreased incidence or elimination of disease/organism e.g. smallpox, polio
Bad:
- Decreased exposure to pathogen -> decreased immune stimulus -> decreased amtibody -> increased susceptibility -> outbreak
- Later average age of exposure -> increased severity e.g.. polio, hep A, chicken pox, congenital rubella syndrome
How does immunodeficiency affect infections?
Increase in frequency and severity
What other diseases is immunodeficiency associated with?
Autoimmune diseases
Malignancy
What age group are most people who are diagnosed with immunodeficiency?
> 50% >18
What is an immunocompromised host?
State in which the immune system is unable to respond appropriately and effectively to infectious microorganisms
Qualitative or quantitative defect of one or more components of the immune system
What are the key components of the innate immune system?
Innate barriers
Phagocytes
Complement
What are the key components of the adaptive immune system?
B cells and antibodies
T cells
How are immunodeficiencies recognised and diagnosed?
Infections suggesting underlying immune deficiency defined as “SPUR”:
- S - severe
- P - persistent
- U - unusual
- R - recurrent
How are immunodeficiencies classified?
Primary - Intrinsic defect - Single-gene disorder/ polygenic/ polymorphism
Secondary - Underlying disease or condition affecting immune components - decreased production/ increased loss or catabolism
How can primary immunodeficiencies be further classified?
B cell
T cell
Phagocytes
Complement
What is the incidence rate of immunodeficiencies?
1:400 - 1:400000
Occur in the first month of life
80% patients <20 yrs
70% male
What is the most common B cell immunodeficiency disease?
Common variable immunodeficiency - Inability of B cells to mature to plasma cells
What is impaired B cell development known as?
Bruton’s disease (X-linked)
What is the presentation of patients with primary antibody deficiencies?
Recurrent upper and lower respiratory bacterial infections -> bronchiectasis
GI complications including infections (Giardia)
Arthropathies (including Mycoplasma/Ureaplasma sp)
Increased incidence of autoimmune disease
Increased incidence of lymphoma and gastric carcinoma
What is the management of a patient with primary antibody deficiencies?
Prompt/prophylactic antibiotics
Immunoglobulin replacement therapy
Management of respiratory function
Avoid unnecessary exposure to radiation
What is the presentation of patients with primary phagocyte deficiencies?
Prolonged and recurrent infections: Skin and mucous membranes Osteomyelitis Deep abscesses Commonly staphylococcal (catalase +ve) Invasive Aspergillosis Inflammatory problems (granuloma)
What is the management of a patient with primary phagocyte deficiencies?
Prophylactic antibiotics/anti-fungal gents
Interferon-g (CGD)
Steroids (CGD)
Stem cell transplantation
What is Di George syndrome?
Lack of thymus - defect in thymus embryogenesis and incomplete development => T cell deficiency
What is severe combined immunodeficiency?
Absence of functional T-lymphocytes which results in a defective antibody response due to either direct involvement with B-lymphocytes or due to improper activation of the B cells due to non-functional T helper cells.
Most severe form of immunodeficiency. Multiple types depending on gene mutated
What are the symptoms of DiGeorge syndrome?
CATCH-22 Cardiac abnormalities Abnormal facies Thymic hypoplasia Cleft Palate Hypocalcaemia 22 is the chromosome abnormalities
What is the management of DiGeorge syndrome?
Neonatal cardiac surgery Supplement to correct hypocalcaemia If <4 cellmicrolitre, prophylaxis with antibiotics Bone marrow transplantation Use only X-raddiated and CMV (-) blood No live vaccines
How does SCID present?
Failure to thrive Protracted diarrhoea Hepato-splenomegaly 90% of SCID have low lymphocyte count High susceptibility to fungal and viral infections
What viral infections are common in patients with SCID?
Pneumocystis pneumonia Varicella-zoster virus Herpes viruses Cytomegaloviruse Epstein Barr virus
What is the management of a patient with SCID?
Short term: - no vaccines - only irradiated CMV-blood products - aggressive treatment of infections - prevention of new infections - prophylactic antibiotics and anti-fungals IVIG Long term: - bone marrow / stem cell transplantation - gene therapy
What does a deficiency in C1, 2 or 4 compliment components cause?
Immune-complex disease
What does C3 complement component deficiency cause?
Recurrent bacterial infection
What causes recurrent Neisserial infection?
C5, 6, 7, 8 or 9 compliment component deficiencies
What might cause a secondary immune deficiency?
Malnutrition Infection Liver disease Lymphoproliferative diseases Drug-induced neutropenia Splenectomy
What factors might cause neutropenia?
Drugs Autoimmune infections Bone marrow infiltration with malignancy Aplastic anaemia Vitamin 12/folate/iron deficiency Chemotherapy Exposure to chemical agents Radiotherapy
What is the management of neutropenia?
Treat suspected neutropenic sepsis as an acute medical emergency and offer emeperic antibiotic therapy immediately
Assess patient’s risk of septic complications
What is an asplenic patient more at risk of?
Increased susceptibility to encapsulated bacteria
OPSI (overwhelming post-splenectomy infection) => sepsis and meningitis
What is the management of an asplenic patient?
Penicillin prophylaxis
Immunisation against encapsulated bacteria (at least 2 weeks after splenectomy if poss)
Patient information; Medic alert bracelet
What are the immune functions of the spleen?
Blood borne pathogens
Antibody production - acute: IgM, long term: IgG
Splenic macrophages remove opsonized microbes and remove immune complexes
What might cause increased loss or catabolism of immune components?
Protein-losing conditions - nephropathy, enteropathy
Burns
How is the specific type of immunodeficiency recognised and diagnosed?
Age Sex Site(s) and frequency of infection(s) Type of organism(s) Sensitivity and type of treatment Family history
What are the investigations carried out to diagnose an immunodeficiency?
Full blood count and differential
Exclusion of secondary immunodeficiency
Tests of humoral (antibody) immunity
Tests for cell mediated immunity - lymphocytes
Tests for phagocytotic cells - neutrophils
Tests for complement
Definitive tests - molecular testing and gene mutation
