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I.D. Pearls 2010. James R. Johnson, MD VA Medical Center University of Minnesota Minneapolis, MN. What I Will Cover…. Antibiotic Armageddon Basic principles Common fake-outs Myths and urban legends Tools of the trade Blood cultures, culture reports Specific conditions Diabetic foot

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I.D. Pearls 2010

James R. Johnson, MD

VA Medical Center

University of Minnesota

Minneapolis, MN

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What I Will Cover…

  • Antibiotic Armageddon

  • Basic principles

  • Common fake-outs

  • Myths and urban legends

  • Tools of the trade

    • Blood cultures, culture reports

  • Specific conditions

    • Diabetic foot

    • Staph. aureus bacteremia

    • Cellulitis

    • C. difficile

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We are here

Antibiotic Armageddon

New Antimicrobials



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New drugs

No drugs

“E.S.C.A.P.E.” Bugs

  • Enterococcusfaecium

  • Staph. aureus (MRSA)

  • Clostridium difficile

  • Acinetobacter baumanii (MDR)

  • Pseudomonas (MDR)

  • Enterobacteriaciae (MDR)

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Basic Principles

  • Define the pathogen

    • Any culture (from relevant site) beats none

    • Contact outside labs for early culture results

    • Reculture if new fever (etc.), new abx

  • Treat the patient, not the culture

  • Match aggressiveness of Rx to severity and tempo of disease

  • Source control

    • Drain, debride, discontinue devices

    • Imaging, interventionalists

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Basic Principles (cont.)

  • Antibiotics are not always benign; use with care

    • Allergy and ADEs (rash, GI, fever, cytopenias, renal, etc.)

    • Drug-drug interactions

      • TMP-SMZ, FQs, flagyl + warfarin --> high INR, bleeding

      • Linezolid + SSRIs --> seretonin syndrome

      • FQs, macrolides + (multiple drugs) --> long QT, torsades

      • FQs, doxy, mino + Ca, Mg, Al, Fe --> drug inactivation

    • Resistance: current bug, next bug, C. difficile, population

  • Treat as narrowly and briefly as possible

  • Contain the contagion (infection control)

  • Prevention (immunize, hygiene, vents & lines…)

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Common Fake-Outs

  • “Cellulitis”

    • Gout, stasis, dermatitis, bug bite

  • “Pneumonia”

    • Edema, effusion, atalectasis, aspiration, fibrosis, tumor, vasculitis, hypersensitivity

  • “UTI”

    • Asymptomatic bacteriuria, pyuria, vaginitis, contaminated sample

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Myths & Urban Legends

  • Taking all the antibiotics will prevent resistance

  • Osteomyelitis requires IV Rx

  • Triple-phase bone scan is good test for osteo

  • Antibiotic stewardship is about $, not patients

  • Best to double-cover Pseudomonas

  • Pyuria indicates clinical importance of bacteriuria

  • Bacteriuria should be eliminated before implants

  • BCs should be timed to match fever spikes

  • IV antibiotics are superior to PO

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Highly Orally Bioavailable Antimicrobials

  • Fluoroquinolones

  • Tetracyclines

  • Fluconazole

  • Metronidazole


  • Clindamycin

  • Linezolid

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Highly orally bioavailable agents include:


2. Gentamicin

3. Vancomycin

4. Fluconazole

5. Cephalexin

6. Metronidazole

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Demystifying Blood Cultures

  • “Set” = 2 bottles (aerobic, anaerobic)

    • Any bug can grow in either bottle

  • Sensitivity of BC

    • Volume, prior abx, organism, inoculum, cont. vs. intermit.

  • Specificity of BC

    • Proportion positive, organism(s), context, time to pos.

    • True: S. aureus, Strep, Pneumo, GNRs, Entc, yeast

    • False: CNS, diphtheroids, P. acnes, Bacillus, Clostridium

    • Variable: Strep viridans

  • Line vs. peripheral BC can help define source

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Demystifying Blood Cultures (cont.)

  • “R/O endocarditis” voodoo

    • just get 2-3 sets

  • Fungal BCs: are for histo, crypto, molds

    • Not Candida (for which routine BCs are fine)

  • AFB BC: AIDS, profound CMI defect

  • Viral BC: now replaced by (quant.) PCR

    • CMV, EBV, parvo B19

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Demystifying Culture Reports

  • First result reported is Gram stain (direct prep)

    • WBC (PMN, monos), epi’s, organisms

  • Next: preliminary culture result

    • “Catalase-pos. GPCs in prs. & clusters resembling Staph.”

    • “Oxidase-pos. GNRs” (code for Pseudomonas)

  • Then: formal ID and sensi’s; now automated

  • Final report may take longer, if multiple orgs.

  • NB: no routine sensi’s on CNS, Strep, low-count UC bugs, diphtheroids

  • Additional sensi’s often available; have to ask

  • “No PO options”--think of PO equivalents

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S. aureus: catalase & coag-pos. GPC

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Pseudomonas: oxidase-pos. GNR

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Common Errors in Interpreting Culture Reports

  • Confusing direct smear with culture

  • Confusing Staph. aureus with coag. neg. Staph.

    • Very different organisms

    • Very different clinical implications

  • Confusing MRSA, MRSE, MSSA, MSSE

  • Waiting for Godot (i.e., sensi’s on CNS, etc.)

  • Assuming culture is final when sensi’s appear on 1 organism from polymicrobial culture

  • Confusing bottles vs. sets (bacteremia)

  • Confusing UA with UC

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Duration of Therapy

  • UTI

    • ABU: none

    • Cystitis

      • Uncomplicated: 3d (women), 5-7d (men)

      • Complicated: 7-14d

    • Febrile UTI, pyelo, acute prostatitis: 7-14d

    • Chronic prostatitis: 4-12 weeks

  • HAP, VAP: 8d (15d if Pseudomonas)

  • CAP: 5-10d

  • Cellulitis: 5-14d

  • Osteo: 6 weeks

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Duration of Therapy (cont.)

  • Bacteremia

    • S. aureus: 14d (?10d?) - 6 weeks

    • CNS: 7d

    • Enterococcus: 14d

    • GNRs: 7-14d

    • Strep, Pneumococcus: 5-7d

  • COPD exacerbation: 7d

  • Acute Lyme, anaplasmosis: 7-10d

  • C. difficile: 10-14d

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Specific Diseases

  • Diabetic foot infection

  • Staph. aureus bacteremia

  • C. difficile

  • Cellulitis

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Diabetic Foot Infection

  • Ulcer is not an infectious disease

  • If clinical evidence of infection, get culture(s)

  • Assess severity & extent of infection

    • Minor, vs. limb-threatening, vs. life-threatening

    • Skin, soft tissues, bone, bloodstream

  • Flora varies (GPC, GNRs, anaerobes)

  • Drain, debride (amputate?), culture

  • May not need extended IV abx; delay PICC

  • Osteo not necessary to define early on

  • Vascularity? Neuropathy? Predisposing f’s?

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Staph. aureus Bacteremia

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Staph. aureus Bacteremia

  • Need to identify (i) source, (ii) metastatic foci

  • High-dose IV Rx; no good PO option

  • Daily BCs; can remain pos. w/o clinical signs

  • -lactams more rapidly cidal than vanco (MSSA)

  • Clinical impression insensitive for IE; need echo

    • Good quality TTE adequate?

  • Spine infection common; low threshold for MRI

  • Duration of Rx for SAB

    • Minimum 14d (?10d if “squeaky clean”?)

    • 4-6 weeks: deep focus, delayed response to Rx, ?MRSA?

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Percent of S. aureus that is Methicillin-Resistant



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Alternatives to Vanco for MRSA

  • IV

    • Linezolid (oxazolidinone)

    • Quinuprisin-dalfopristin (streptogramin)

    • Daptomycin (lipopeptide)

    • Tigecycline (glycylcycline)

    • Telavancin (lipoglycopeptide)

  • PO

    • TMP-SMZ (folate inhibitor)

    • Minocycline, doxycycline (tetracycline)

    • Linezolid

    • Clindamycin (lincosaminide)

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Which are superior to vanco for MRSA bacteremia?

1. Linezolid

2. Daptomycin

3. Tigecycline

4. Quinupristin-dalfopristin

5. Telavancin

6. None of the above

7. Beats me--that’s what ID is for!

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Acute gout

Stasis dermatitis

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  • Usually Staph. aureus or -Strep (A, B, G, C)

  • Reasons for non-response to PO -lactam

    • Insufficient drug levels (dose, absorption, non-adherence)

    • Host factors (vasculopathy, edema, necrosis, abscess)

    • Bug factors (resistance, different bug, polymicrobial)

    • Noninfectious (misdiagnosis)

  • Culture any drainage, bulla, or broken skin

  • Be patient; it often worsens before improving

  • Almost never underlying osteo (skip X-ray)

  • Danger signs

    • Disproportionate pain or toxicity; necrosis; crepitus

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Clostridium difficile

  • “The name game”: CDAD --> CDI

  • Diagnostic tests

    • Toxin insensitive; culture nonspecific & slow; ?fecal WBC?

    • Toxin PCR ~100% sensitive & specific; ?availability?

  • Therapy

    • Mild-moderate: PO flagyl (then PO flagyl, then PO vanco)

    • Severe: PO vanco, aggressive hydration

    • Ileus: PO vanco (high dose), IV flagyl, vanco enema, surgery

  • Recurrences

    • Prevent by avoiding antibiotics; ?probiotics? IgG? Mab?

    • Also: vanco taper, rifaximin chaser, fecal biotherapy (PO, PR)

  • Transmission: isolation, handwashing, env. decon.

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C. difficile Attack Rate & Outcomes

Increasing primary disease

Decreasing treatment success

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Repeated Toxin EIA Testing







Assumes test SN = 73.3%, SP = 97.6%; CDI population prevalence = 10%

Peterson & Robicsek. Annals 2009

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Which is/are true?

1. If the extremity is swollen, red, warm, and tender, the patient has cellulitis.

2. If a wound culture shows 4+ of a pathogenic organism, treatment is indicated.

3. A patient admitted for diabetic foot infection should:

  • undergo MRI or 3-phase bone scan to r/o osteo

  • receive a PICC line for extended IV Rx if osteo is found.

    4. Wound cultures can be helpful despite their limited sensitivity and specificity.

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What I Have Covered

  • Antibiotic Armageddon

  • Basic principles

  • Common fake-outs

  • Myths and urban legends

  • Tools of the trade

    • Blood cultures, culture reports

  • Specific conditions

    • Diabetic foot

    • Staph. aureus bacteremia

    • Cellulitis

    • C. difficile

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Which is/are true? (Your call!)

1. I got some new or different ideas from this talk.

2. I disagree with some of what I heard today.

3. This talk addressed topics of practical relevance to me.

4. I would like more information about some of these topics.

5. I am likely to change my practice in some way based on things I heard today.

6. I will be more likely to consult ID in the future.

7. I will be less likely to consult ID in the future.

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There’s More to I.D. than….