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Introduction to Clinical Infectious Disease Practice


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

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

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
  • Interpret micro lab reports contaminant vs.
    normal flora vs. pathogen
  • Antimicrobial stewardship
  • Infection control

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

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

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
  • Streptococcus gallolyticus bacteremia
  • Neisseria meningitis
  • Recurrent giardiasis
  • Pneumococcemia without pneumonia
  • Non-healing wound

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

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,

common variable immunodeficiency
tumor necrosis factor
Exposures for Clinical ID
  • Indoor - hot tub, recruits/dormitory, GI virus,
  • 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,

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
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

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
  • Human tendency to rely on technology to make the
    diagnosis e.g. nuclear scans, urinalysis

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

The Gram Stain
Gram Stains of Common Bacterial Pathogens
Gram Stains (Cont.)
Acid Fast (Kinyoun) Stain
Mixed Morphology on Culture Plate
Mycology Lab Basics How Fungi Differ from Common
  • 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

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
  • Very little susceptibility testing outside of HIV

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

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
  • 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

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

Consequences in Antimicrobial Rx
  • Liberal or broad spectrum use
  • Conservative or narrow spectrum use
  • Less chance of not covering the etiologic
  • 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,
  • Allows non infectious, or self-limited
    infectious etiologies to be easily recognized

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