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Introduction to Clinical Infectious Disease Practice

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Introduction to Clinical Infectious Disease Practice Applying Microbiology to the Practice of Medicine Key Aspects of Clinical ID Determine if ... – PowerPoint PPT presentation

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Title: Introduction to Clinical Infectious Disease Practice


1
Introduction to Clinical Infectious Disease
Practice
  • Applying Microbiology to the Practice of Medicine

2
Key Aspects of Clinical ID
  • Determine if the patient infected, and with what
  • Determine risk factors or exposures
  • Assess if the patient is contagious/address
    public/preventive health issues
  • Advise for/against invasive, dangerous, or
    expensive procedure(s)
  • Guide empiric and definitive Rx, if any is
    needed, discontinue/avoid uneccesary
    antimicrobials
  • Interpret micro lab reports contaminant vs.
    normal flora vs. pathogen
  • Antimicrobial stewardship
  • Infection control

3
Is the Patient Infected
  • No symptom or sign is 100 specific for infection
  • Easier to know what the patient has if you know
    what he/she doesnt have
  • Common mimics of infection autoimmune diseases,
    hematologic malignancy, drug reactions

4
  • Why this particular organism e.g. look for
    occult colon cancer

5
Infection Looking Beyond the Diagnosis
  • Clinical scenario
  • Additional consideration
  • Occult colon cancer
  • Complement deficiency
  • Common variable immune deficiency
  • Occult myeloma
  • Contiguous osteomyelitis or prosthetic device
    infection
  • Streptococcus gallolyticus bacteremia
  • Neisseria meningitis
  • Recurrent giardiasis
  • Pneumococcemia without pneumonia
  • Non-healing wound

6
Risk Factor Assessment in ID
  • Host immune status
  • Exposures travel, animal, close contacts,
    occupation

7
Risk Assessment in ID
  • Endogenous immune deficiency
  • Exogenous Immune deficiency
  • Extremes of age
  • Cellular immune defect(HIV, alcoholism,
    liver/renal disease)
  • Humoral immune defect(HIV, myeloma, CVID)
  • Anatomic defect(Atopic dermatitis,
    COPD/bronchiectasis, neutropenia, burns)
  • Other immune defects (granulocyte defect or
    deficiency, complement deficiency, Fe overload,
    hyperglycemia/acidosis, pregnancy)
  • Vaccine status
  • Corticosteroids
  • TNF antagonists
  • Organ rejection inhibitors
  • Cancer chemotherapeutics
  • Infectious agents (cytomegalovirus, HTLV1,
    influenza)

common variable immunodeficiency
tumor necrosis factor
8
Exposures for Clinical ID
  • Indoor - hot tub, recruits/dormitory, GI virus,
    healthcare
  • Outdoor woods, zoo, local vs. distant travel
  • Animals obvious (pets, work) vs. less obvious
    (ticks, mosquitoes, rodents)
  • Geography endemic mycoses, parasites
  • Prior Rx antimicrobials (false negative
    cultures, allergic reaction, C. difficile), or
    mask key signs or symptoms (analgesics,
    antipyretics)

9
Public Health and ID
  • Immediate contagion risk TB, zoster, anthrax,
    plague, scabies
  • Potential or future exposure influenza, group A
    strep, RMSF, MRSA, C. difficile, multi-drug
    resistant organisms
  • Laboratory personnel coccidioides, tularemia,
    hemorrhagic fever viruses
  • Tracking of exposed (PPD, STD partners)

Rocky mountain spotted fever Methicillin
resistant s. aureus
10
Guiding Patient Evaluation Dollars and Danger,
Tissue is the Issue
  • Decision to do a test or procedure can be
    influenced by financial gain, workload,
    incomplete understanding of diagnostic rationale
    or risk/benefit ratio
  • Since ID docs dont perform the procedures and
    dont read the scans, minimal bias can exist
  • Lack of specific diagnosis must be weighed
    against risk of test/procedure
  • Specific diagnosis, removal or drainage of
    infected sites may improve healing but not be
    justified

11
Micro Lab Results for the Clinician
  • Many docs have unrealistic expectations or
    limited understanding of clinical labs
  • Micro in particular so, because of added
    parameters of contaminants, normal flora,
    fastidious growth, effects of antimicrobials
  • Serologic, histological and nuclear (PCR) testing
    can have varying sensitivity and specificity for
    different organisms and from different labs
  • Susceptibility results require clinical
    correlation
  • Human tendency to rely on technology to make the
    diagnosis e.g. nuclear scans, urinalysis

12
Pitfalls in Micro Lab Culture Results
  • Do not assume nurses or physicians know optimal
    specimen type, collection technique, or what
    organisms to pursue
  • Tissue, fluid always preferred over swab
  • No technique is beyond contamination, and few
    organisms are always clinically relevant by there
    mere presence
  • Antibiotics can affect results even if given
    within weeks

13
The Gram Stain
14
Gram Stains of Common Bacterial Pathogens
15
Gram Stains (Cont.)
16
Acid Fast (Kinyoun) Stain
17
Mixed Morphology on Culture Plate
18
Mycology Lab Basics How Fungi Differ from Common
Bacteria
  • Fungi generally grow slower
  • Environmental contaminants common
  • Candida spp. often expected flora
  • Susceptibility testing far less reproducible or
    clinically correlated
  • Many pathogenic molds rarely isolated from blood

19
Virology Lab Basics
  • Too inefficient to routinely culture many
    relevant viruses
  • Viruses causing chronic infection (e.g. herpes
    CMV) can be detected by serology, histology or
    culture yet still not be clinically relevant
  • PCR assays expanding beyond clinical correlative
    data
  • Very little susceptibility testing outside of HIV

20
Basic Serologic Responses
21
Complement Fixation Serology
22
Infection Control
  • Goes along with antibiotic stewardship
  • Recognize trends in drug-resistant isolates,
    nosocomial infections
  • React to contagious pathogens, outbreaks (e.g.
    swine flu)

23
General Rules for Antimicrobial Use
  • Cheapest, narrowest spectrum agent with the most
    clinical data preferred
  • Such a selection optimized by knowing exact Dx,
    and/or likely organisms involved
  • No one or even 2 drugs can cover every
    possibility
  • All antibiotic usage, no matter how efficient,
    will result in some degree of serious morbidity
    and promote drug-resistant isolates
  • Empiric Rx. Must weigh risk of inappropriate or
    unnecessary use and above consequences

24
Antimicrobial Stewardship
  • Tempting, but impractical for ID docs to
    completely control use of certain drugs in hopes
    of minimizing inappropriate use
  • Colleagues will learn from our approach-
    especially with new drugs communicate our
    rationale for Rx choices

25
Consequences in Antimicrobial Rx
  • Liberal or broad spectrum use
  • Conservative or narrow spectrum use
  • Less chance of not covering the etiologic
    agent(s)
  • Improves outcomes in situations where any delay
    in starting Rx. increases mortality
  • Greater costs, more side effects, drug resistance
  • If patient improves on multiple IV drugs, but no
    definite diagnosis made many err on liberal side
    for continuing or completing
  • May miss window for initiating Rx
  • May be inadequate to cover resistant or
    unexpected etiology
  • Minimizes cost and adverse drug reactions,
    resistance
  • Allows non infectious, or self-limited
    infectious etiologies to be easily recognized

26
Disk Diffusion MIC
-Inexpensive, -Cant be automated, -Good
clinical correlation except for
fastidious organisms
27
E-Test for MICs
-Antibiotic gradient -Expensive -Best for 1 or 2
drug testing or fastidious organisms
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