Infectious diseases Flashcards
What is systemic inflammatory response syndrome? SIRS
SIRS - 2/4 below
- temp >38 or <36
- HR >90
- RR > 30 or CO2 <32mmhg
- WCC >12,000 or <4000
What is sepsis and septic shock?
Sepsis - infection + 2 of (tachypnea, low BP, altered mental status)
Septic shock - sepsis + vasopressors + lactate >2
What is the transition of infection/SIRS into sepsis influenced by?
- organisms virulence and burden
- immune system: age, immune suppression
- organ vulnerability
- timeliness of interventions
In the steps leading up to sepsis, what influences pathogen entry and survival?
- tissue contamination
- foreign body insertion
- immune status
What does activation of the innate immune system involve?
- pro inflammatory cytokines, TNF-a, il1+6 activate immune cells
- ROS, NO, proteases - bacterial killing, vasodilation and permeability
- complement activated, mediates activation of leukocytes to attack organism
During infection, what alterations occur in the coagulation and endothelial system?
Activated endothelium - adhesion and migration, tissue edema
Coagulations - alterations = increase in procoagulant factors, and reduced anticoagulants
How does sepsis cause relative and absolute reduction in circulating volume?
Vasodilation and increased permeability
What organ dysfunctions are associated with sepsis?
Heart: reduced contractility, hypo perfusion and shock
Pericapillary edema - impaired oxygen delivery
How can bacteremia be classified? (5)
- site of origin - primary = endovascular, 2’= extravascular
- duration - transient, intermittent and continuous
- type - gram +ve/-ve, polymicrobial etc
- place of acquisition - community acquired or nosocomial
- patient groups - well, nosocomial, elderly, immunosuppressed
What are the exogenous mediators of bacteremia and septic shock?
Endotoxin - lipopolysacharide of gm-ve bacteria
Gram +ve - lipotechoic acid and peptidoglycan
Viruses - lyse host cells, complement and cell death and proinflammatory response via CD14/TLR3 or TLR4
What are signs and symptoms of sepsis/bacteremia in patients?
- abrupt onset
- shaking, chills, rigor
- fever on hypothermia
Less common - dyspnoea, delirium, renal failure, rash/toxic shock/DIC/purpura fulminant
How is a diagnosis of bacteremia made?
3 collections of blood cultures
- from different venopuncture sites within first 2 hours of presentation
- at least one aerobic and one anaerobic
What is the treatment of sepsis?
Pathogen - broad spectrum beta lactam usually started early then switch to most effective agent following pathogen identification
Host - IV fluids, inotropic, mechanical ventilation, glucocorticoids to curb inflamm.
How can sepsis be prevented for community acquired and nosocomial bacteraemia?
Community - vaccines
Nosocomial - minimising iatrogenic infection, hand hygiene, ventilator, IV, catheter mgmt
What can cause immunocompromised?
- Disease - acute leukaemia, AIDS, RA, diabetes
2. Iatrogenic - chemotherapy, DMARDs, steroids
What cells are involved in cell mediated and humoral immunity?
Cell mediated - neutrophils, NK, monocytes
Humoral - Antibodies, complement, lysosyme
What is mild, moderate and severe neutropenia?
Mild: 1000-1500 cells/uL
Mod: 500-1000 cells/uL
Severe: <500 cells/uL
What are causes of neutropenia? and what are the associated defects?
Inherited
Acquired: drug induced cytotoxics, bone marrow irradiation, cancer related, plastics anaemia
Defects - chemotaxis, opsonisation, intracellular killing
What are the effects of bone marrow irradiation/chemotherapy on the immune system?
Following irradiation, 14 days of neutropenia
First 12 days - chemo causes mucositis, so higher risk of gram -ve, streptococci, fungi and HSV infection
Later - graft vs host disease can develop where donor cells attack the body — immunosuppressants are given which immunosuppressed cell mediated immunity even more
How may a patient with neutropenic sepsis present?
- fever
- hypothermia
- hypotension
- clinical deterioration
What is a neutropenic fever?
temp >38.3 C OR sustained temp >38C for more than 1 hour, occurring in a patient with neutrophil count <500 cells/uL
Incidence of fever in a neutropenic patient increases with:
- severity of neutropenia
- prolonged duration of therapy
- comorbid factors, catheter, mucositis, use of monocloncal a/b
What are the most common causes of neutropenic fever and sites of infection?
Causes - gm-ve bacilli (P.Aeruginosa) and now gm+ve (s. aureus, s. epidermis, streptococci and enterococci)
Sites: bacteremia, pneumonia, pharyngitis, sinusitis, perianal lesions, skin lesions
How is a febrile neutropenic patient evaluated?
Evaluated: microbiology with 2+ sets of cultures, sputum and urine gram stain and culture AND imaging - CXR+ CAT
