Infection Flashcards
Give some examples of ways a patient could get an infection
STI Vector Airborne droplets Contaminated food or water From another part of the patient
What is an infection and how does it cause disease?
Invasion of a hosts tissue by microorganisms.
Disease caused by microbial multiplication, toxin production and host response
What is the difference between horizontal and vertical transmission?
Horizontal is via contact/inhalation/ingestion
Vertical is mother to child before or after birth
What are the stages of disease?
Exposure, adherence, invasion, multiplication, dissemination
What are some determinants of disease?
Pathogen - virulence factor, inoculum size and anti microbial resistance
Patient - site and co morbidities
How do we know if a patient has an infection?
History - symptoms/exposure
Examination - organ dysfunction
Investigation - full blood count, C-reactive protein, imaging
What are the 4 types of microbe?
Virus, bacteria, fungi and parasites
What are the different types of virus?
DNA/RNA, Single/double strand, enveloped/non enveloped
What are some different types of bacteria?
Crocus, spirillus, bacillus
Give some examples of types of parasites and fungi
Parasite - Protozoa/worms
Fungi - yeast/molds
Outline an infection model
A patient and pathogen come together and an infection occurs. It is then managed before an outcome is reached
How could we class antibacterial drugs?
Bactericidal/bacteriostatic
Broad/narrow spectrum
Target side
Chemical structure
What would be the ideal features of an anti microbial?
Selective toxicity, few side effects, reaches site of infection, can be given orally or IV, long half life and doesn’t interfere with other drugs
What are the main classes of antibiotic and give an example of each
Cell wall synthesis - B lactam/glycopeptide
Protein synthesis - tetracycline, aminoglycoside, macrolide
Cell membrane function - polymixin
Nucleic acid synthesis - quinolones
Outline the mechanism of action for penicillin
Inhibit the penicillin binding proteins which stops the catalysing of cross links in bacterial cell walls
How can antibiotic resistance develop?
Drug inactivating enzymes produced
Target altered
Uptake altered - decrease permeability/increase efflux
What is SIRS?
Systemic inflammatory response syndrome Any two of: Temperature 38 Heart rate >90/min Respiratory rate >20/min WBC 12x10^9
What is bacteraemia?
Presence of bacteria in the blood
What is sepsis?
Systemic response to infection - SIRS + documented/suspected infection
What is severe sepsis and septic shock?
SIRS + organ dysfunction/hypoperfusion
Sepsis + low BP despite receiving IVF
Outline the inflammatory cascade
Endotoxins stimulates local production of cytokines to start inflammatory response and promote wound repair. They enter the circulation and stimulate GF, macrophages and playelets to try and restore homeostasis.
SIRS - homeostasis not restored
How is coagulation caused in SIRS and what are the potential consequences?
Cytokines initiate thrombin production and inhibit fibrinolysis. Causes microvascular thrombosis and therefore ischaemia, dysfunction and failure
What other investigations should be done to confirm sepsis?
FBC, PCR, CRP, blood sugar, liver function, blood gas
What are the sepsis six?
High O2 flow Blood cultures IV antibiotics Serum lactate IVF resuscitation Urine output measurement
What are some potential complications of sepsis?
Irreversible hypotension Respiratory failure Renal failure Increased inter cranial pressure Ischaemic necrosis
What are some methods of preventing sepsis?
Vaccine
Antibiotic prophylaxis
What is the immune system?
Cells and organs that contribute to immune defences against infectious and non infectious conditions
What is an infectious disease?
When a pathogen succeeds in evading and/or overwhelming a hosts immune defences
What are the roles of the immune system?
Recognise pathogens
Contain/eliminate infection
Regulate itself
Remember pathogens
What are the differences between the innate and the adaptive immune system?
Innate: fast, recognises groups of pathogens, no memory, no intensity change
Adaptive: slow, recognises one pathogen, immunological memory, increasing intensity
What is the first line of defence?
Barriers - physical (skin), physiological (vomiting), chemical (low pH), biological (normal flora)
What is the second line of defence?
Phagocytes, chemicals and inflammation
Outline the steps involved in destroying a bacteria
Adherence of microbe to phagosome
Ingestion by phagocyte forming a phagosome
Fuse phagosome with lysosome
Digest with enzymes
Residue put in body and removed from cell
What are healthcare infections?
Infections that arise as a consequence of health care
What are things that can be done to the patient to prevent healthcare infections?
Optimise their condition
Antimicrobial prophylaxis
Physical barriers - isolate/protect
What are some things that can be done for healthcare workers and the environment to prevent healthcare infections?
Make sure workers are healthy and vaccinated
Clean the surfaces and medical equipment. Good food hygiene
What is the importance of taking a travel history?
Imported diseases
Different strains
Infection prevention
What are the causative organisms and the transmission route for malaria?
Plasmodium falciparum, vivax, ovale and malariae
Female mosquito
What are some signs and symptoms a malaria patient will present with?
1-3 week incubation
Headache, cough, malaise, arthalgia, myalgia, fatigue
Fever, sweats and chills in a 3-4 day cycle
Few signs +- splenomegaly
What investigations should be done if you suspect malaria?
Blood smear, FBC, LFT, U+E, glucose
How do you treat malaria?
Falciparum - quinine/artemisinin
Others - chloroquine +- primaquine
How can malaria be prevented?
Assess risk
Bite prevention
Chemoprophylaxis
What is main causative organism for enteric/typhoid fever and what is the transmission route?
Salmonella enterica - gram -ve cocci
Foecal oral from food/water
What signs and symptoms do you expect to see in a patient suffering from typhoid fever?
Fever, headache, abdominal discomfort, constipation, dry mouth, rash, hepatsplenomegaly
7-14 day incubation
What investigations should be done for typhoid fever?
Anaemia, lymphopenia, LFT, blood and faecal culture
How would you treat typhoid fever? And prevent it?
Azuthromycin or ceftriaxone
Food/water hygiene and vaccine
Describe the HIV virology
Enveloped, single stranded, RNA retrovirus
Describe the pathogenesis of HIV
The viral RNA is transcribed to ssDNA and integrated into the host cell genome
How is HIV diagnosed?
Presence of virus antibodies in the blood
PCR on a genome
What are the types of drugs used to treat HIV?
Fusion inhibitor, entry inhibitor, reverse transcriptase inhibitor and integrate inhibitor
Describe the virology of Hep B
Enveloped DNA virus
How can hep B be transmitted?
Mother to infant, sexual, percutaneous
Describe the change in incidence of symptomatic and chronic infections as age changes
More likely to get symptoms as you get older (from <10% up to 50%) but less likely to get a chronic infection (from 90% down to 3%)
How is Hep B prevented?
Vaccine
Describe the virology of Hep C
Enveloped, ssRNA virus
How is Hep C transmitted?
Mainly blood borne
Occasionally vertical or sexual
How is Hep C treated?
With the aim of curing - antivirals, interferons and ribavarin
What is CRP?
An acute phase protein produced by the liver
How does presence of a pathogen lead to acute phase proteins production?
Pathogen –> macrophage/monocytes –> cytokines (IL-6) –> liver –> acute phase proteins
What is the function of CRP?
Opsonisation - enhance binding
What is CRPs clinical use?
Rapidly produced and easy to measure in response to infection, trauma, surgery, burns, infarction, inflammation and cancer
What are microbiota?
Micro-organisms carried on skin and mucosal surfaces that are normally harmless or beneficial
How can a patient infect themselves? Give an example of each route
Invasion - strep pyogenes - pharyngitis
Migration - E. coli - UTI
Inoculation - coag negative staphylococcus - joint infection
Haematogenous - viridans strep - endocarditis
Give examples of external and internal infections
Cellulitis, pharyngitis, conjunctivitis
Endocarditis, osteomyelitis
Give examples of prosthetic infections and the causative organism
Prosthetic valve endocarditis - coag -ve staphylococci
Joint infections - coag -ve staph and staph aureus
Pacing wire - coag -ve staph and staph aureus
Explain the pathogenesis of a surface infection
Adhere to host cells/prosthetic surface using pili or fimbriae
Biofilm formation
Invade and multiply
Host response - pyogenic or granulomatous
What is the problem with bio films?
Difficulty in removing bacteria
How do you diagnose surface infections and what are some challenges?
Blood culture
May need sonication
They adhere and may be low numbers
How do you treat surface infections and what are some challenges?
Sterilise or remove the surface
Poor penetration due to biofilm and the risks of surgery
How do you prevent surface infections?
Maintain surface integrity, prevent/remove colonisation
Define hypersensitivity
Antigen specific immune responses that are inappropriate/excessive and result in harm to the host
Explain the two phases of hypersensitivity reactions
Sensitisation phase - first exposure
Effector phase - clinical pathology upon re-exposure
What type of hypersensitivity is an allergy?
Type 1
Name some common allergens
Mites, pets, pollen, insect venom, medication and food
Outline the pathway leading to an allergic response
Plasma cells produce IgE and this along with irritants stimulate mast cells to produce histamine, cytokines, leukotrienes and prostaglandins which cause an increase in vascular permeability, vasodilation and bronchial contraction
How is an allergic reaction diagnosed?
History and testing blood for mast cell products
Skin prick and challenge tests
What are some visible allergic reactions?
Wheel and flare
Urticaria
Angioedema
Wheezing
How does an epipen work?
reverse vasodilation and airway obstruction and inhibit mast cells
How do you manage allergic reactions?
Remove allergen
Educate - epipen use, symptom recognition
Medic alert bracelet
Drugs - antihistamine, corticosteroids, anti IgE, epipen
Allergen desensitisation
Give examples of source - person, person - person and vector - person conditions
Food - food poisoning, environment - legionella, animals - rabies
Influenza, norovirus
Mosquito - malaria/dengue, tick - Lyme disease
Define endemic rate, outbreak, epidemic and pandemic
Background rate
2+ cases linked by time and place
Rate of infection greater than the background rate
Very high rate of infection spanning countries and continent
What is R0?
Average number of cases one case generates in uninfected, non immune population
What are some reasons behind outbreaks?
New pathogen - new antigens/antibiotic resistance
New host - none immune
New practise
What interventions can be done to prevent outbreaks?
Remove pathogen - decontaminate/sterilise or kill vector
Improve patient health - nutrition, medication, vaccination
Improve practise - protective clothing, behaviour (safe sex and needles)
Environment - clean water and air
What are the consequences of Antimicrobial resistance?
Treatment and prophylaxis failure
Economic costs
What methods to achieve Antimicrobial stewardship are in place?
Persuasive - educate and remind
Restrictive - formulary restriction and authorisation
Structural - computer records and expert advice
What microbes cause disease in cystic fibrosis and the order they occur in?
H influenza
Staph aureus
Burkholderia cepacia
Explain cystic fibrosis
Autosomal recessive defect in the CFTR protein causing less chloride to move into the mucus and therefore making it thicker. This blocks ducts and gets colonised
How does diabetes increase risk of infections?
Hyperglycaemia and acidaemia - reduce humoral immunity and lymphocyte/leukocyte function.
Micro/macrovascular - causes poor perfusion and infection
Neuropathy - less sensation so ulcers and skin infections. Incomplete bladder emptying cause UTIs
Define immunodeficiency
State in which the immune system is unable to respond appropriately and effectively to infectious microorganisms
What are the criteria for diagnosing immunodeficiency?
Spur
Severe, persistent, unusual, recurrent infections
What are the types of primary immunodeficiencies in order of commonness?
B cell - 50%
T cell - 30%
Phagocyte - 18%
Complement 2%
Give some examples of B cell problems
Common variable immunodeficiency - B cells don’t mature to plasma
IgA deficiency - B cells don’t become IgA
Bruton’s disease - impaired B cells
Hyper IgM
How might a patient with immunoglobulin deficits present? How are they managed?
Recurrent respiratory infections and GI problems
Prophylactic antibiotics, immunoglobulin replacement therapy, manage respiratory function
Give some examples of phagocyte deficiencies
Leukocyte adhesion deficient
Chronic granulomatous disease - no respiratory burst
How might a patient with phagocyte deficiency present? How are they managed?
Recurrent infections - ulcers, abscesses, invasive aspergillosis
Antibiotics, antifungals, immunise, surgery, stem cells
Chronic granulomatous disease - interferon and steroids
Give examples of T cell deficient conditions
Di George - no thymus
Severe combined immunodeficiency
How is Di George diagnosed and managed?
Catch 22 - cardiac abnormalities, abnormal facies, thymol hypoplasia, cleft palate, hypocalcaemia, 22 chromosome
Neonatal cardiac surgery, give Ca2+ supplements, bone marrow and antibiotics
Give an example of a complement deficiency
C1 inhibitor deficient
Hereditary angio oedema
Give some causes of secondary immunodeficiencies
Reduced immune components - malnutrition, infection, liver, neutropenia, splenectomy
Increased loss or catabolism - burns and protein losing conditions
What is the spleens function?
Kill encapsulated pathogens - H influenza, strep pneumoniae, neiserria meningitidis
Produce IgM and IgG
Remove opsonised microbes and immune complexes
