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
How is febrile neutropenic patient managed?
MGMT:
Urgently broad spectrum antibiotics IV (cover pseudomonas)
- tazocin (or cefepime or ceftazidime)
- + vancomycin if MRSA/patient in shock
- targeted treatment when pathogen identified
If fever persists past day 4 of a/b then consider fungal infection
- yeast (candida)
- mould (aspergillus, fusarium, zygomycetes)
Empiric anti fungal therapy = voriconazole, amphoterecin B, caspofungin
What are 3 ways to prevent neutropenic infection?
- modify environment - +ve pressure room, no flowers
- Meticulous line mgmt
- prophylaxis - A/B, antifungals, anti viral
What are the 3 stages at which infection can occur following solid organ transplant?
- Nosocomial/technical (donor or recipient) <1 month
- Activation of latent infection 1-6month
- Community acquired >6 month
What is the importance of the spleen in immune function?
- Produces IgM memory B cells
- sequesters opsonised encapsulated bacteria
- modulates effects of cytokines released during sepsis
What infections are splenectomy patients at risk of getting?
- encapsulated bacteria
- malaria and babieosis
- capnocytophagia
- S. aureus and gram -ve’s
How might patients with overwhelming post splenectomy infection present?
- fever, shivering, myalgia
- vomiting, diarrhoea, headache
- septic stick, DIC, multi organ failure
- Death (40-70% within in 24hours)
Patients with hyposplenia/splectomy have a 5% lifetime risk of developing:
Sepsis, pneumonia, meningitis
What is the mgmt and prevention of OPSI?
MGMT - recognise symptoms, resuscitation with fluid, cultures (blood, urine, CSF), empiric antibiotics - CEFTRIAXONE +VANCOMYCIN to cover s. pneumoniae, N. meningitides, H. influenza
Prevention - vaccinate, prophylactic a/b, SOS antibiotics (amoxycillin)
