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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

I.D. Pearls 2010

James R. Johnson, MD

VA Medical Center

University of Minnesota

Minneapolis, MN

what i will cover
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
antibiotic armageddon

We are here

Antibiotic Armageddon

New Antimicrobials



e s c a p e bugs

New drugs

No drugs

“E.S.C.A.P.E.” Bugs
  • Enterococcusfaecium
  • Staph. aureus (MRSA)
  • Clostridium difficile
  • Acinetobacter baumanii (MDR)
  • Pseudomonas (MDR)
  • Enterobacteriaciae (MDR)
basic principles
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
basic principles cont
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…)
common fake outs
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
myths urban legends
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
highly orally bioavailable antimicrobials
Highly Orally Bioavailable Antimicrobials
  • Fluoroquinolones
  • Tetracyclines
  • Fluconazole
  • Metronidazole
  • Clindamycin
  • Linezolid
highly orally bioavailable agents include
Highly orally bioavailable agents include:


2. Gentamicin

3. Vancomycin

4. Fluconazole

5. Cephalexin

6. Metronidazole

demystifying blood cultures
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
demystifying blood cultures cont
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
demystifying culture reports
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
common errors in interpreting culture reports
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
duration of therapy
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
duration of therapy cont
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
specific diseases
Specific Diseases
  • Diabetic foot infection
  • Staph. aureus bacteremia
  • C. difficile
  • Cellulitis
diabetic foot infection
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?
staph aureus bacteremia24
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?
alternatives to vanco for mrsa
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)
which are superior to vanco for mrsa bacteremia
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!


Acute gout

Stasis dermatitis

  • 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
clostridium difficile31
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.
c difficile attack rate outcomes
C. difficile Attack Rate & Outcomes

Increasing primary disease

Decreasing treatment success

repeated toxin eia testing
Repeated Toxin EIA Testing







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

Peterson & Robicsek. Annals 2009

which is are true
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.

what i have covered
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
which is are true your call
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.

there s more to i d than
There’s More to I.D. than….