Intro to ID 1 Flashcards
What is a commensal?
- a microorganism that is a normal inhabitant of the human body
- either microbe or host derives benefit
- neither is harmed
What is a pathogen?
- a microorganism capable of causing disease
- includes commensals and noncommensals
What temperature indicates a fever?
38 C (100.4 F)
What is the main non-infectious cause of a fever?
Drug-induced
malignancies, blood transfusions, auto-immune disorders
What are the causes of false-negative fevers?
absence of a fever when a patient actually has an infection
- antipyretics
- corticosteroids
Overwhelming infections may cause patient to be hypothermic
What are the systemic signs of an infection?
- hypotension (SBP <90)
- tachycardia (>90 bpm)
- tachypnea (>20 RPM)
- fever (>38C or <36C)
- increased/decreased WBC
At least two of the bottom 4 criteria are needed to meet SIRS
What are the systemic symptoms of an infection?
- chills
- rigors (cold sweats)
- malaise
- mental status changes
What local signs and symptoms indicate an infection?
- symptoms referable to specific body system (flank pain)
- pain and inflammation
- inflammation in deep-seated infections
May be absent in neutropenic patients
What is the normal range for WBCs?
4,500 - 11,000 cells/mm^3
What are the non-infectious causes of elevated WBCs?
- steroids
- leukemia
stress, RA, pregnancy
What are the functions of mature neutrophils?
PMNs, polys, segs
- most common WBC
- fight infections
What are the functions of immature neutrophils?
bands
- increased during infection = “left shift”
What are the functions of eosinophils?
0-8% of WBCs
- involved in allergic reactions & immune response to parasites
What are basophils associated with?
0-3% of WBCs
- associated with hypersensitivity reactions
What are lymphocytes associated with?
20-40% of WBCs
- humoral (B-cell) & cell-mediated (T-cell) immunity
What are the functions of monocytes?
0-11% of WBCs
- mature into macrophages
- serve as scavengers for foreign substances
What is leukocytosis and what infections is it associated with?
- increased neutrophils +/- bands
- associated with bacterial infections
What is leukopenia?
abnormally low WBC that may be a sign of overwhelming infection
poor prognostic sign
What is lymphocytosis and what infections is it associated with?
- increased in B-cells and T-cells
- associated with viral, fungal, or tuberculosis infections
What is ANC?
Absolute Neutrophil Count
- total number of circulating segs and bands
- segs are mature neutrophils which have segmented nucleus
- bands are immature neutrophils which lag that feature
What is neutropenia?
- ANC <500 cells/mm^3
or - ANC expected to decrease to <500 cells/mm^3 in the next 48 hours
ANC <100 cells/mm^3 is termed profound neutropenia
Why is ANC important?
- risk of infection dramatically increases as ANC decreases
- start to worry when ANC is <1000 cells/mm^3
- ANC < 500 is associated with substantial risk of infection
What are the acute phase reactants that are evaluated when assessing for infection?
- ESR (erythrocyte sedimentation rate)
- CRP (C-reactive protein)
- PCT (procalcitonin)
How are ESR and CRP used in the diagnosis of infection?
erythrocyte sedimentation rate
- elevated in the presence of an inflammatory process; however, it does NOT confirm infection
- often elevated in presence of infection, so serial measurements can be useful to determine response to treatment
What are the normal ESR ranges?
- 0-15 mm/hr –> males
- 0-20 mm/hr –> females
What is the normal CRP range?
0-0.5 mg/dL
What is the role of PCT (procalcitonin) in the diagnosis of infections?
- magnitude of elevation provides useful diagnostic information
- more specific for bacterial infections than the acute phase reactants
- serial measurements every 1-2 days useful to assess response to therapy and when to d/c abx
What do the different ranges of PCT indicate?
- <0.05 mcg/L –> normal
- <0.25 mcg/L –> low risk of infection
- > 0.5 mcg/L –> antibiotics should be continued
Differentiate between colonization and infection:
- colonization is when a potentially pathogenic organism is present at the body site but is not invading host tissue or eliciting a host immune response
- infection is when a pathogenic organism is present at the body site and is damaging host tissue and eliciting host responses and symptoms consistent with an infection
Define MIC:
minimum inhibitory concentration
Minimum inhibitory concentration is the lowest antimicrobial concentration that prevents visible growth
What is a breakpoint?
A breakpoint is an MIC or zone diameter value used to categorize an organism as susceptible, susceptible-dose dependent, intermediate, resistant, or non-susceptible
Define Susceptible (S):
- Isolates with an MIC at or below or a zone diameter at or below the (S) breakpoint are inhibited by the usually achievable concentrations of antimicrobial agent when normal dosing regimens are used
- (S) indicates it will likely result in clinical efficacy
Define susceptible-dose dependent (S-DD):
S-DD implies susceptibility is dependent on the dosing regimen used
Define Intermediate: I
Isolates with MICs approach achievable blood or tissue concentrations and response rates may be lower than for susceptible isolates
Define resistant (R):
- isolates not inhibited by usually achievable concentrations of agent with normal dosage schedules
- clinical efficacy has not been reliably demonstrated
Define non-susceptible (NS):
- used for isolates for which only susceptible breakpoint is designed
- if MIC is above or zone diameter is below the susceptible breakpoint, isolate is categorized as NS
Which test is the gold standard when identifying a pathogen?
MIC testing (broth dilution)
What is the drawback of using disk diffusion (Kirby-Bauer) for susceptibility testing?
CANNOT derive a MIC from the zone of inhibition
Only results are susceptible, intermediate, or resistant
What are key things to remember when evaluating the results of susceptibility tests?
- Look for drugs that say S or S-DD
- MICs are unique to bug-drug combos and therefore they CANNOT be compared between abx
What is the benefit to automated testing systems?
saves space
Which rapid diagnostics test for bloodstream infections gives a susceptibility profile?
PhenoTest BC Kit
What is empiric therapy?
- starting abx before identification and susceptibility results are known
- the abx selected should cover most common pathogens
- usually very broad coverage and may require 2-3 different abx
What is directed (targeted) therapy?
- abx therapy selected after organism identification and/or susceptibility is known
What is the difference between empiric and targeted therapy?
- empiric is just the first abx we pick before we know anything
- targeted is picked based upon test results
What is de-escalation?
- process of empiric –> directed
- selecting an abx with the narrowest spectrum of activity
Can be stepwise or all at once
What is spectrum of activity?
what anti-microbial does the drug cover
What is an antibiogram?
- annual summary of institution-specific anti-infective susceptibility
- used to pick empiric options
What is the rule of thumb when picking an empiric therapy off an antibiogram?
Pick a therapy with at least 80% of susceptibility
Which genetic variations are important to consider during antibiotic selection?
- G6PD deficiency
- HLA-B*5701 allele
How is antibiotic therapeutic response monitored?
- culture and sensitivity reports
- WBC, temp, physical complaints
- therapeutic drug monitoring (serum concentration)
What are the factors to consider in antibiotic selection?
- Indication
- Source
- Pathogens
- Spectrum of Activity
- Resistance patterns
- PK/PD parameters
- Monitoring parameters
- Duration of therapy
Infections scare people so really practice memorizing drugs
Define antimicrobial resistance:
AR
AR occurs when germs develop the ability to defeat the drugs designed to kill them
germs - bacteria, fungi, viruses, or parasites
What is the purpose of antimicrobial stewardship?
AMS
- optimize clinical outcomes while minimizing unintended consequences
- reduce healthcare cost without adversely impacting quality of care
What are the core elements for an AMS program?
- Leadership commitment
- Accountability –> PharmD or MD
- Pharmacy expertise
- Action
- Tracking
- Reporting
- Education
What are examples of AMS strategies?
- antibiotic de-escalation
- requiring approval from ID Steward prior to use of certain abx
- antibiotic timeout
- creation of optimized order sets for different disease states
