Treatment of MRSA: IDSA Treatment Guidelines and Beyond - Vance G. Fowler, Jr., MD, MHS

Treatment of MRSA:
IDSA Treatment Guidelines and Beyond

      Vance G. Fowler, Jr., MD, MHS

Disclosures
   Will discuss commercial products and/or
    services

   Will discuss off-label or investigative product
    use

Disclosures
     Nature of Relevant Financial
                                                            Commercial Interest
               Relationship
                                          Astellas, Cubist, Merck, Theravance, Cerexa, Pfizer,
Grant or research support                    Novartis, Advanced Liquid Logics, National
                                             Institutes of Health
                                          Astellas, Cubist, Inhibitex, Merck, Johnson &
                                             Johnson, Leo Pharmaceuticals, NovaDigm, The
Paid consultant
                                             Medicines Company, Baxter Pharmaceuticals,
                                             Biosynexus, MedImmune, Galderma, Inimex
Speaker’s Bureau                          Cubist
Employment                                Duke University
                                          Arpida, Astellas, Cubist, Inhibitex, Merck, Pfizer,
Honoraria                                     Targanta, Theravance, Wyeth, Ortho-McNeil,
                                              Novartis, Vertex Pharmaceuticals
Membership on advisory committees or      Cubist – advisory committee
  review panels, board membership,
  etc.
Ownership Interest (e.g., stocks, stock   NONE
  options or other interests
Other relevant financial interests        NONE

Approved Treatment Options 2012
     Bacteremia:              Vancomycin
                               Daptomycin

     Pneumonia:               Vancomycin
                               Linezolid

     Soft Tissue Infection:   Vancomycin
                               Linezolid
                               Daptomycin
                               Ceftaroline
                               Tigecycline
                               Telavancin

Do Guidelines for MRSA Matter?
Brindle et al J Antimicrob Chemotherap 2009; 64: 1111–3

   Multisite retrospective
    comparison of 28-day
    all cause mortality in                      P = 0.73

    1675 patients with
    MRSA bacteremia
    before and after
    UK National MRSA
    Treatment Guidelines

Does Expertise Matter?
ID Consultants Improve Outcome of S. aureus Bacteremia

Fowler Clin Infect Dis 1998; 27(3):478-86. Prospective cohort of 244 patients
Compliance with IDC associated with less Recurrent SAB (P

The Most Important Aspect of MRSA
Treatment is to Make the Right Diagnosis

Points of this Talk

   Make the Right Diagnosis

   Bacteremia & Endocarditis

   Pneumonia

   Soft Tissue Infection

Points of this Talk
   Make the Right Diagnosis

   Bacteremia & Endocarditis

   Pneumonia

   Soft Tissue Infection

S. aureus Bacteremia

   Key Issue: Complicated or Uncomplicated?

Uncomplicated MRSA Bacteremia

Uncomplicated MRSA Bacteremia
DEFINITION
 Exclude endocarditis with echocardiography
 Defervesce in 72h
 Follow-up Blood culture negative
 No prosthetic material (pacer, valve, arthroplasty)
 No evidence of metastatic infection

TREATMENT: at least 2 weeks with vancomycin or
  daptomycin (6mg/kg IV)

TAKE HOME PAY:
Uncomplicated MRSA Bacteremia

   Not common

   Not benign

   If you think someone has it and treat
    someone for it, be sure you are right.

Complicated MRSA Bacteremia

Complicated SAB is Common

      Frequency in 724 Duke
            patients
             43%

                   Fowler, et al. Arch Intern Med. 2003;163:2066-2072.

Complicated SAB is Complicated

                                                               Infective endocarditis
                                                               Septic arthritis
                 12%                                           Deep-tissue abscess
                                                               Vertebral osteomyelitis
                                                               Epidural abscess
                                                               Septic thrombophlebitis
Patients (%)*

                       7.4%                                    Psoas abscess
                                                               Meningitis
                              5.7%                             Other complications

                                     3%
                                             2.5%       2.4%                          2.4%
                                                                  2.2%      1.7%

                n=89   n=54   n=41   n=22    n=18      n=17      n=13      n=12      n=16

                                            Fowler, et al. Arch Intern Med. 2003;163:2066-2072.

Identifying Complicated S.
aureus Infection

Identifying Complicated SAB
                             Scoring Systems Matter
                      100                                                       90
                                                                      80
     Probability, %

                      80                                    70

                      60
                                               40
                      40               30

                      20        15

                       0
                                0       1       2           3         4          5
                                                    Score

 1 point                    Community-acquired
                            Skin examination suggesting acute systemic infection
                            Persistent fever at 72 hours

2 points                    Positive follow-up blood cultures at 48-96 hours
                                                            Fowler, Arch Intern Med, 2003;163:2066-72.

Identifying Complicated SAB
Clinical Context Matters
SAB + Median Sternotomy = Trouble
Blood culture   Postoperative Postoperative       LR+ (95%CI)
results         Mediastinitis  Mediastinitis
                Present (n=98) Absent
                               (n=757)
S. aureus       46             14                 25
                                                  (14.7-44.4)
Other           15             111                1.0
Pathogen                                          (0.64-1.71)
No Growth       37             632                0.46
                                                  (0.36-0.58)
                                       Fowler, Circulation 2003; 108: 73-78

Identifying Complicated SAB
  Devices Clinical Context Matters Matter
S. aureus Bacteremia + Prosthesis = Trouble

     SAB + Arthroplasty = 28% Joint Infection
              Murdoch et al Clin Infect Dis 2001; 32:647-9.

         SAB + Prosthetic Valve = 51% Valve Infection
               El-Adhab Am J Med 2005; 118:225-9.

     SAB + Pacemaker/ICD = 45% Device Infection
              Chamis Circulation 2001; 104: 1029
     .

     SAB + Central Catheter = 71% Thrombophlebitis
               Crowley Crit Care Med 2008;36:385-90
     .

Identifying Complicated SAB:
How You Look Matters
Rate of IE Diagnosed by TEE

                          IE Diagnosed by TEE       30

                                                    25

                                                    20

                                                    15

                                                    10

                                                    5

                                                    0
              Fowler (n=103)    Rasmussen (n=244)

Lessons Learned:
Clinical Identifiers of Complicated SAB
     Things to bank on:
          All SAB is Complicated SAB until Proven otherwise
     Things to always do:
          Get Follow-up Blood cultures
          Get an Echo
     Things to look for:
          Persistent Bacteremia
          Persistent Fever
          Community acquisition
          Clinical Evidence of complications
          Post-operative State
     Things to Fear:
          Pain
          Prostheses

Points of this Talk
   Make the Right Diagnosis

   Bacteremia & Endocarditis

   Pneumonia

   Soft Tissue Infection

TREATMENT
MRSA Bacteremia & Endocarditis
Uncomplicated MRSAB: Vanco or Dapto
     “at least 2 weeks”

Complicated MRSAB: 4-6wks

Endocarditis: Vanco or Dapto x 6 wks
“Some experts recommend higher dosages of daptomycin at 8-
  10mg/kg IV once daily”

“Addition of gentamicin to vancomycin is not recommended for
  bacteremia or native valve endocarditis”

“Addition of rifampin to vancomycin is not recommended for
  bacteremia or native valve endocarditis”

MRSA Prosthetic Valve IE

Methicillin-Resistant:
           - Vancomycin                   x 6-8wks
           - Rifampin 900mg/d             x 6-8wks
           - Gent 3mg/kg daily            x 2 wks

Baddour Circulation 2005;111:e394-e434.

When?   Who?

Valve Surgery: Randomized Trial?

Inclusion Criteria
1)   Periannular Complications
2)   New Onset Atrio-ventricular
     Block
3)   New Severe Valvular
     Insufficiency
4)   Early Onset Prosthetic IE
5)   S. aureus IE

Early Surgery Improves Survival for Native Valve
IE

                              Lalani et al Circulation 2010; 121:1005-13

Early Surgery Improves Survival in Propensity-
Matched Patients with Heart Failure

                         Keifer et al JAMA 2011; 306(20):2239-2247

Linezolid for Persistent MRSA Bacteremia
Jang Clin Infect Dis 2009; 49:395-401.
   Observational study comparing patients with PMRSAB
    (>7d) salvaged with Linezolid or Vanco
   Linezolid-treated patients had higher rates of:
    - Early microbiological response: 75% vs. 17%; p=0.006
    - LONGER duration of Bacteremia 26.4 + 38.8d vs. 11.8 + 3.9d
    - Salvage Response: 88% vs. 0%; p

Treatment: MRSA Osteomyelitis
   Surgical debridement “whenever feasible”

   Antibiotics:   IV: vancomycin, daptomycin
                   PO: TMP-SMX + Rif
                        Linezolid
                        clindamycin

   Optimal duration: Unknown but at least 8wks

Treatment:
Device-Related Osteoarticular Infection
   Early onset (

Vancomycin

Response: Increased Vancomycin
Dosing
      Troughs of 15-20 mcg/mL for severe infections1
        – Trough > 10 mcg/mL for all MRSA infections due to
          association with hVISA
        – 15-20 mcg/mL  improved outcomes2

      Loading dose of 25-30 mg/kg in severe infections
        – Risk of overshooting target
               Consider lower loading dose in older patients or those with
                potential occult renal issues: consider 20-25 mg/kg
        – Difficult in larger patients

1. Rybak M et al. Am J Health-Syst Pharm. 2009;66:82-98.
2. Kullar R et al. Clin Infect Dis. 2011;52:975-81.

Higher Vancomycin Dosing and
Troughs May Cause Nephrotoxicity
   Predictors          of vancomycin nephrotoxicity
    Characteristic                       Odds Ratio (95% CI)   P value
    Vancomycin serum trough > 14         3.18 (2.31-4.37)      < 0.001
    mg/L
    Vancomycin therapy duration > 7      1.89 (1.39-2.56)      < 0.001
    days
    Baseline Cr > 1.7                    3.00 (2.16-4.18)      < 0.001

 Pritchard L et al. Am J Medicine 2010; 123: 1143-1149                   38

IDSA GUIDELINES POSITION:
How should results of vancomycin
susceptibility be used to guide therapy?

“For isolates with a vancomycin MIC <
2ug/ml…, the patient’s clinical response should
determine the continued use of vancomycin,
independent of the MIC.”

Take Home Pay:
    Vancomycin
   New uses favor higher troughs, probably at
    the expense of adverse events

   Association between Vancomycin MIC of S.
    aureus & Clinical Outcome is Present but
    Complex

   Remains standard treatment for MRSA IE

Points of this Talk
   Make the Right Diagnosis

   Bacteremia & Endocarditis

   Pneumonia

   Soft Tissue Infection

MRSA Pneumonia
  - Community Acquired
  - Healthcare-Associated

Community-acquired pneumonia

   “For hospitalized patients with severe
    community-acquired pneumonia defined
    by any of the following: (1) a requirement
    for intensive care unit (ICU) admission, (2)
    necrotizing or cavitary infiltrates, or (3)
    empyema, empirical therapy for MRSA is
    recommended…”

Healthcare-Associated MRSA
Pneumonia

   “…IV Vancomycin (A-II) or linezolid 600mg
    po BID (A-II) or clindamycin 600mg PO/IV
    TID (B-III), if the strain is susceptible, is
    recommended for 7-21 days, depending on
    the extent of infection.”

Linezolid: Pros and Cons
        Pros                                                       Cons
          – Excellent Oral                                            – FDA Black box warning for
                                                                        increased mortality concerns in
            Bioavailability
                                                                        catheter-BSI trial*
          – Pneumonia                                                 – Myelosuppression – duration
                                                                        dependent >2wks
          – Novel mechanism
                                                                      – Serotonin syndrome esp with SSRI,
          – Resistance low                                              MAO-inhibitors, ca
            (will likely change                                       – Optic neuritis
            after 2015)
                                                                      – Lactic acidosis
Stevens DL, et al. Expert Rev Anti Infect Ther. 2004;2(1):51-59
Aneziokoro CO, et al. J Chemother. 2005;17(6):643-650.
Rao N, et al. Diagn Microbiol Infect Dis. 2007;59(2):173-179.
Bernstein WB, et al. Ann Pharmacother. 2003;37(4):517-520.
Waldrep TW, et al. Pharmacotherapy. 2002;22(1):109-112.
*FDA. Available at: http://www.fda.gov/cder/drug/infopage/linezolid/default.htm.

Linezolid & S. aureus Pneumonia

Wunderink Chest 2003; 124(5):1789-97

   Randomized, Double-Blind Controlled Multicenter trial of
    Linezolid IV or Vanco for MRSA healthcare-associated or
    hospital-acquired pneumonia
   Non-inferiority with superiority (Efficacy)
   Primary Endpoint: Clinical Cure at End of Study in evaluable
    Per Protocol patients
   Clinical Cure: -resolved signs/symptoms pneumonia
              -stable/improved chest imaging
                     -no additional antibiotics
   Per Protocol: all mITT patients meeting study criteria,
    received adequate antibiotic therapy, and had outcome

   1225 pts enrolled from 150 sites in 4 continents

Efficacy Outcomes

Outcomes: No Difference in Mortality in
Linezolid vs. Vancomycin-Treated Patients

Safety Outcomes

CONCLUSIONS
   Cure rates in PP and mITT patients with MRSA HAP
    were higher in patients treated with LNZ vs. VAN
    (58% v. 47%; p=0.42)
   Significance lost in HCAP, HAP, & VAP subgroups*
   Nephrotox higher in VAN (18.2%) vs. LNZ (8.4%)
   No difference in mortality
   MY TAKE: LNZ probably does have clinical
    advantages for MRSA HAP, but not sure if it is worth
    the cost (resistance, $)
   GAME-CHANGER?: Patent Expiration 2015

                           *Torres Clin Infect Dis 2012;54(5):630–2

Points of this Talk

   Make the Right Diagnosis

   Bacteremia & Endocarditis

   Pneumonia

   Soft Tissue Infection

Most CA-MRSA Infections
     are Skin Infections

Fridkin et al NEJM 2005;352:1436-44

Skin and Soft Tissue Infections
  – Incision & Drainage
    Essential and Sometimes Sufficient

  – Antibiotics indicated for:
    severe/multiple disease
    multiple sites of infection,
    rapid progression,
    systemic illness;
    comorbidity or immunosuppression,
    face, hand, or genitalia,
    associated phlebitis,
    lack of response to I& D

Skin and Soft Tissue Infections (2)
Purulent Cellulitis:
“…empirical therapy for CA-MRSA is recommended
pending culture results. Empirical therapy for infection
due to β-hemolytic streptococci is likely to be unnecessary
(A-II). Five to 10 days of therapy is recommended but
should be individualized…”

 Non-Purulent Cellulitis:
 “…empirical therapy for infection due to β-hemolytic
 streptococci is recommended (A-II). Empirical coverage
 for CA-MRSA is recommended in patients who do not
 respond to β-lactam therapy and may be considered in
 those with systemic toxicity.”

Summary: S. aureus Skin & Subcutaneous Abscesses
   Incision and Drainage most important

   Purulent cellulitis
 - Empirical therapy for CA-MRSA pending culture.
 - Empirical therapy for strep unnecessary.

   Non-Purulent cellulitis
 - Empirical therapy for strep recommended
 - MRSA role unknown

   Coverage of both strep + MRSA:
 - Clindamycin
 - TMP-SMX/Tetracycline + β-lactam
 - Linezolid

Skin and Soft Tissue Infections (3):
Empiric MRSA Coverage

  Outpatients                 Inpatients
    clindamycin                 Vancomycin (IV)
    TMP-SMX                     Linezolid
                                daptomycin
    Doxycycline/Minocycline
                                telavancin
    Linezolid                   clindamycin
                                ceftaroline*

Points of this Talk

   Make the Right Diagnosis

   Bacteremia & Endocarditis

   Pneumonia

   Soft Tissue Infection

Extra Slides

TMP-SMX-DS vs. CA-MRSA

       PRO                 CON
                      Poor vs. S. pyogenes
    CA-MRSA
     susceptible      Photosensitivity
                      Rash – Stevens-Johnson
    Dose?            K+ & creatinine
                      Aseptic meningitis
    Cheap
                      G6PD deficiency - hemolysis

Reduced Efficacy of TMP-SMZ
1) Resistance: Altered target enzymes*
2) Exogenous thymidine from pus
                                                           DH folate*
                                                         reductase TMP

           PABA                             folic acid            folinic
                                       =                          acid
                    SMX             dihydro-
                                    pteroate synthetase*

                      Pus: exogenous                          thymidine,
                           thymidine                     purine, DNA
Proctor Clin Infect Dis 2008; 46: 584-93.

Doxycycline/Minocycline vs CA-MRSA

  PRO                 CON
                      +/- vs. S. pyogenes
  MostMRSA       

  susceptible        Photosensitivity

                     Resistance on therapy
                      (Efflux pump)
  BID
                     Pediatric

Doxycycline, but Not Minocycline,
Induces its Own Resistance in USA 300
   tet(k) encodes drug-inducible efflux pump
    conferring resistance to tetracycline & doxycycline
    but not minocycline
   Subinhibitory Doxy induced resistance to doxy but
    not mino in tet(K) +/ tet(M) – USA300 MRSA

                                Schwartz Clin Infect Dis 2009; 48:1483–4.

Clindamycin vs. CA-MRSA

       PRO                        CON
   80 % or more              C. difficile
    susceptible in vitro      Inducible resistance due
   Covers Strep.              to MLSB
    pyogenes                   (Macrolide/Lincosamide/
   Inhibits toxin             Streptogramin)
    synthesis

Telavancin
   Once-daily glycopeptide
   Activity against MRSA, VISA, VRSA
   FDA-approved (2009) for Complicated Skin & Skin
    Structure Infections
   Side effects: Nephrotoxicity, Taste Disturbances, Avoid
    In Pregnancy

D-zone test for Inducible Clindamycin
      Resistance due to MLSB

                       E      CC

-Perform on all erythro-R, clinda- S S. aureus isolates
-Treatment failures have occurred
- Found on same S. aureus gene as mec A; high % of
MRSA resistant to erythromycin

Ceftaroline: “Pros” and “Cons”

             Pros                                    Cons
   Anti-MRSA Cephalosporin            No Activity vs. Pseudomonas,
                                        ESBL, Acinetobacter
   Bactericidal vs. Gram Pos
    (MRSA, VISA, S. pyogenes)
    & Gram Neg bacteria

   Twice daily dosing

   Non-Inferior to comparator in
    cSSSI & Pneumonia
                                          Kanafani. Future Microbiol 2009; 4; 25-33.

“Add-omycins”
(Gentamicin, Rifampin)

Add Gentamicin?
        In vitro synergy BUT
          – No data that impacts mortality
          – Associated with nephrotoxicity in daptomycin
            study when combined with either ASP or
            vancomycin
                Median duration: 4 days
                Clinically significant decrease in CrCl occurred in
                 8% of dapto-treated pts vs. 22% of comparator
                 patients

Korzeniowski & Sande. Ann Intern Med. 1982;97:496; Cosgrove SE et al. Clin Infect Dis. 2009;48:713-21.

Add Gentamicin?
Low Dose, Short Course Gent for SAB is
Nephrotoxic

  …we recommend
  against the use of
  initial low-dose
  gentamicin in the
  management of most
  cases of S. aureus
  bacteremia and
  native valve
  endocarditis …

                         Cosgrove Clin Infect Dis. 2009; 48: 713-721.

Addition Rifampin?

   No evidence for better outcomes

   Significant evidence for ↑↑ resistance & ↑↑ side
    effects
                                           Rifampin No Rifampin P-Value
  Emergence of Resistance*                    21%*              0%   < 0.001
  Increased LFTs**                             23%              2%   0.014
  Drug Interactions***                         52%              0%   < 0.001
* All had been started on rifampin before blood cultures had cleared
** All had concomitant HCV
Levine D et al. Ann Intern Med. 1991;115:674.
Riedel DJ et al. Antimicrob Agents Chemother. 2008;52:2463-7.

Take Home Pay:
Gentamicin / Rifampin for Native Valve
Staph IE

• No evidence for benefit

• Significant evidence for ↑↑ resistance & ↑↑ side
  effects

Property     Vancomycin      Quinupristin       Linezolid      Daptomycin       Tigecyclin     Telavancin     Ceftarolin
               Generic            /              Pfizer           Cubist            e          Theravanc          e
                             dalfopristin                                         Pfizer       e/ Astellas     Cerexa/
                                 King                                                                           Forest

Drug class   Glycopeptide    Streptogramin     Oxazolidone      Lipopeptide     Glycylcyclin   (Lipo)glyco-     5th gen.
                                                               First-in-class        e            peptide     cephalospor
                                                                                                                   in

Mechanism       Slowly       Bacteriostatic   Bacteriostatic    Bactericidal    Bacteriostat   Bactericidal   Bactericidal
of action     bactericidal   Cidal if MLS-                                           ic         (Multiple)

Resistance   hVISA (?),          Rare             Rare         5%- SAB trial       Rare           Rare             ?
             VRSA, VISA                         Plasmid-        Treatment-
                                                 Asstd,          emergent
                                               Treatment-
                                                emergent
Cost          ~ $15/day        ~$300/d          ~$150/d          ~$130/d         ~$200/d        ~$150/d            ?

Indication      cSSSI         cSSSI, VRE         cSSSI            cSSSI            cSSSI          cSSSI        ABSSSI
               HAP/CAP                          CAP HAP         SAB / RIE          Intra           HAP          CAP
              Bacteremia                                                        abdom CAP
             Osteomyelitis

Dosing         IV    BID      Central IV         BID IV        IV, once daily     IV, BID       IV, Once        IV BID
                                 TID              ORAL                                            daily

Key issues   Nephrotoxic       Arthalgia          SSRI           Skeletal         NICHE?         NICHE?          Safe
              ”Red man”        Phlebitis       Interaction       Muscle           Nausea
              syndrome        Central IV      Myelosuppress     Eosinophilic      Not for
             Poor clinical                         ion          Pneumonia       Bacteremia
                effect                         Patent End       Vanco-Dap         Covers
                                                  2015          Resistance         ESBL

Property         Torezolid      Delafloxacin      Dalbavancin      Oritavancin     Ceftobiprole      Amadacycline      Iclaprim
                   Trius            Rib-X            Durata       Medicines Co.        J&J         Novartis/Para        Acino
                                                                                                        tex

Development      Phase III        Phase II          Phase III       Phase III       Approvable        Phase II            ?
stage                            Completed                        (SOLO I & II)       letter         Completed
                                                                                         ?

Drug class       2nd Gen       Fluoroquinolone      2nd gen       Glycopeptide       4th gen.      Tettacycline     Diaminopyri-
               Oxazolidone                        Glycopeptide                     cephalosporin                       midine

Mechanism of   Bacteristatic     Bactericidal      Bactericidal    Bactericidal     Bactericidal    Bactericidal     Bactericidal
action

Spectrum       Gram-Positive    Gram + / G-       G+ (No VRE)     Gram-Positive       G+/G-            Gram +            Rare
                                                                    (no VRE)       Pseudomonas

Indications       ABSSSI           ABSSSI            ABSSSI          ABSSSI           ABSSSI           ABSSSI          ABSSSI
                                                                                     HAP CAP
                                                                                   Failed in VAP

Dosing            PO, IV           IV, BID         IV, 2 Doses    IV Single dose      IV, TID          PO/ IV       IV, twice daily
                Once Daily                       1gm x 1; 500mg                                      Once daily        Oral in
                                                       x1                                                           development

Key issues      Once daily                              ?            ? Safety      Complicated                      Failed CSSSI
                    PO                               Safety       Long Half Life    syntheses                       FDA AB Board

               Effective vs.                                                       Infusion Time                        May be
                Linezolid-                                                                                           resubmitted
                Resistant                                                                                           +/- 1 new trial
                                                                                                                    with new FDA
                                                                                                                        ABSSI
                                                                                                                      Guidance

Fusidic Acid Resistance in S. aureus
Causing Infections in Greek Children

Characteristics of 532 Patients with S. aureus Bacteremia (SAB)
According to Antibiotic Treatment Received: A Prospective
Cohort Study Performed in Australia
Holmes NE et al. J Infect Dis. 2011;204:340–47.

Use of a Simple Criteria Set for Guiding
Echocardiography in Nosocomial S. aureus Bacteremia
Kaasch AJ, Fowler, VG, et al. Clin Infect Dis. 2011; 53:1–9

                                                   - Europe   - USA

                        - Prolonged bacteremia >4 days
                        - Intracardiac devices (PV, ICD, PCM)
                        - Hemodialysis dependence
                        - Spinal infection/nonvertebral osteomyelitis

Relative frequency of infective endocarditis by number of
positive criteria in patients with nosocomial SAB
Kaasch AJ, Fowler, VG, et al. Clin Infect Dis. 2011; 53:1–9

Use of a Simple Criteria Set for Guiding TEE in
Nosocomial S. aureus Bacteremia
Kaasch AJ, Fowler, VG, et al. Clin Infect Dis. 2011; 53:1–9