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Skin and Soft Tissue Infections in the ED


Guest post by Dr. Krishan Yadav

Cellulitis and erysipelas – collectively referred to as skin and soft tissue infections (SSTIs) – are a seemingly simple entity to manage. Yet the burden of SSTIs and the complexity of this disease process may surprise you!

From 1997 to 2005, the number of Americans seeking medical care for SSTIs increased by 50%, totalling 14.2 million visits in 2005 alone.1 Although Canadian data is lacking, a single Vancouver ED diagnosed 2234 patients with a SSTI between January 2003 and September 2004.2 Hospitalization for complicated SSTIs result in an average cost of $8023 with a mean hospital length of stay of 4.9 days.3 Despite this increasing burden, current evidence is lacking regarding optimal management. A recent Cochrane review concluded that the optimal antimicrobial therapy for SSTIs remains unclear, as no two RCTs (of the 25 studies identified) compared the same two antibiotic regimens. Furthermore, outpatient management of SSTIs initially seen in the ED varies widely.4 Lack of evidence regarding the best management is highlighted by the fact that the most current guidelines for managing cellulitis are based on expert opinion.5-7

Diagnosing Necrotizing Fasciitis: Is the LRINEC Score Useful?

·       It is critical that you do not miss the diagnosis of necrotizing fasciitis (NF) given the associated mortality rate of 25 – 35%.
·      The original derivation study of the LRINEC (Laboratory Risk Indicator for NECrotizing fasciitis) score, a retrospective cohort study, reported a PPV = 92% and a NPV = 96%.8
·       The authors proposed that the LRINEC score is a useful tool to diagnose NF:
  

Variable
Score
CRP (mg/L)
³15

4
WBC (/mm3)
15 – 25
>25

1
2
Hb (g/L)
110 – 135
<110

1
2
Na (mmol/L)
< 135

2
Serum Cr (mmol/L)
>141

2
Glucose (mmol/L)
>10

1
Interpretation
Low Risk
Intermediate Risk
High Risk
< 5
6 – 7
>³ 8

Table 1. LRINEC Score

·     However, the only external validation study of the LRINEC score in the ED setting (Note: pending publication) reported a sensitivity of only 52% (38 – 66%).Ultimately, necrotizing fasciitis remains a clinical diagnosis.

MRSA: Risk Factors and Novel Therapies

·       The prevalence of MRSA in Canada is unknown (it is not a reportable disease).
·       At The Ottawa Hospital, 18% of SSTIs that can be cultured are MRSA positive.
·    A study in the ED of The Ottawa Hospital identified community acquired MRSA risk factors that you should consider in your patients.10



Risk Factors
Odds Ratio
95% Confidence Interval
Hepatitis C
13.9
3.5 – 55
Substance Abuse
10.5
4.4 – 25.1
Previous MRSA / known colonization
12.3
1.6 – 97.5
Antibiotics in past 1 year
3.1
1.5 – 6.6
Homelessness in past 1 year
15.6
3.5 – 68.8
Communal living
11.5
2.6 – 51.1
Incarceration
11.5
2.8 – 45.8

Table 2. CA-MRSA: Risk Factors


·       There are novel once-weekly antibiotics (dalbavancin, oritavancin) that are active against typical pathogens plus MRSA.



Dalbavancin
Oritavancin
Structure
Semisynthetic analogs of teicoplanin and vancomycin
Mechanism
Inhibit cell wall synthesis (bactericidal)
Spectrum
MSSA, MRSA, Streptococci, Enterococci
Half-Life
2 weeks
Dose
1 g IV (day 1)
500 mg IV (day 8)
1.2 g IV (single dose)
Cost (USD)
$1100 – 1300
(500 mg vial)
$2600
(1.2 g vial)

Table 3. Characteristics of Once-Weekly Antibiotics

·       Two large non-inferiority RCTs found that dalbavancin is non-inferior to vancomycin-linezolid11, and that oritavancin is non-inferior to vancomycin.12

Cellulitis: Who Should Get IV Therapy? Who should be admitted?

·       The treatment failure rate of SSTIs in Canadian EDs is approximately 20%.13,14
·       ED observation units are of limited value for determining whether a patient should be admitted or managed as an outpatient – one study found that 29.2% of patients are subsequently admitted anyway.15
·       ED physicians most commonly cite a need for IV antibiotics as the primary reason for admitting patients to hospital, yet the rate of serious adverse events with out of hospital treatment is rare (0.5%).16
·     A Canadian ED study13 found 5 risk factors associated with treatment failure for cellulitis (fever, chronic leg ulcers, lymphedema, prior cellulitis in the same area, and cellulitis at a wound site) – consider these factors when deciding on admission vs. outpatient therapy.

Take Home Points

Necrotizing Fasciitis is a clinical diagnosis:
·       The sensitivity of the LRINEC score is unacceptable for use in the ED.
·       Consider adjuncts if you have a high clinical suspicion: CT, MRI or ultrasound.

There are MRSA Risk Factors you should consider for your patients:
·        Hepatitis C, substance abuse, previous MRSA infection/colonization, antibiotics in past year, homelessness in past year, communal living, incarceration.

Novel Once-Weekly Antibiotics are Non-Inferior to Conventional Therapy against MRSA:
·       Dalbavancin and Oritavancin are FDA approved (could be in Canada soon!).
·       Once-weekly antibiotics have the potential to revolutionize the way SSTIs are managed.

Which patients require hospital admission? Who Should Get IV versus Oral Antibiotic Therapy for SSTIs? It is still UNCLEAR!
·       There is a significant evidence gap: we do not know who actually requires admission versus inpatient stay.
·       There is even less guidance for optimal route of antibiotic therapy.
·       This is a big deal: the treatment failure rate for SSTIs in Canadian EDs is 20%.
o   This suggests that there is LOTS of research still to be done!



Original Grand Rounds Video








Dr. Krishan Yadav is a 5th year Emergency Medicine resident at the University of Ottawa, with a special interest in Clinical Epidemiology.

Edited by Dr. Shahbaz Syed, 4th year Emergency Medicine resident, University of Ottawa


References
1. Hersh AL, Chambers HF, Maselli JH, Gonzales R. National trends in ambulatory visits and antibiotic prescribing for skin and soft-tissue infections. Arch Intern Med 2008;168:1585-91.
2. Stenstrom R, Grafstein E, Romney M, et al. Prevalence of and risk factors for methicillin-resistant Staphylococcus aureus skin and soft tissue infection in a Canadian emergency department.[Erratum appears in CJEM. 2009 Nov;11(6):570]. CJEM, Can 2009;11:430-8.
3. Pollack CV, Jr., Amin A, Ford WT, Jr., et al. Acute bacterial skin and skin structure infections (ABSSSI): practice guidelines for management and care transitions in the emergency department and hospital. J Emerg Med 2015;48:508-19.
4. Kilburn SA, Featherstone P, Higgins B, Brindle R. Interventions for cellulitis and erysipelas. Cochrane Database Syst Rev 2010:CD004299. doi: 10.1002/14651858.CD004299.pub2.
5. Stevens DL, Bisno AL, Chambers HF, et al. Practice guidelines for the diagnosis and management of skin and soft tissue infections: 2014 update by the Infectious Diseases Society of America. Clin Infect Dis 2014;59:e10-52. doi: 10.1093/cid/ciu444.
6. Eron LJ, Lipsky BA, Low DE, Nathwani D, Tice AD, Volturo GA. Managing skin and soft tissue infections: expert panel recommendations on key decision points. J Antimicrob Chemother 2003;52:i3-17.
7. CREST Guidelines. 2005.
8. Wong CH, Khin LW, Heng KS, Tan KC, Low CO. The LRINEC (Laboratory Risk Indicator for Necrotizing Fasciitis) score: a tool for distinguishing necrotizing fasciitis from other soft tissue infections. Crit Care Med 2004;32:1535-41.
9. Burner E. The Laboratory Risk Indicator for Necrotizing Fasciitis Lacks Sensitivity for Patients with Necrotizing Fasciitis Who Present to the Emergency Department: An External Validation Study. Ann Emerg Med 2012;60:S120.
10. Vayalumkal JV, Suh KN, Toye B, Ramotar K, Saginur R, Roth VR. Skin and soft tissue infections caused by methicillin-resistant Staphylococcus aureus (MRSA): an affliction of the underclass. CJEM 2012;14:335-43.
11. Boucher HW, Wilcox M, Talbot GH, Puttagunta S, Das AF, Dunne MW. Once-weekly dalbavancin versus daily conventional therapy for skin infection. N Engl J Med 2014;370:2169-79. doi: 10.1056/NEJMoa1310480.
12. Corey GR, Kabler H, Mehra P, et al. Single-dose oritavancin in the treatment of acute bacterial skin infections. N Engl J Med 2014;370:2180-90. doi: 10.1056/NEJMoa1310422.
13. Peterson D, McLeod S, Woolfrey K, McRae A. Predictors of failure of empiric outpatient antibiotic therapy in emergency department patients with uncomplicated cellulitis. Acad Emerg Med 2014;21:526-31.
14. Murray H, Stiell I, Wells G. Treatment failure in emergency department patients with cellulitis. CJEM 2005;7:228-34.
15. Volz KA, Canham L, Kaplan E, Sanchez LD, Shapiro NI, Grossman SA. Identifying patients with cellulitis who are likely to require inpatient admission after a stay in an ED observation unit. Am J Emerg Med 2013;31:360-4.
16. Talan DA, Salhi BA, Moran GJ, et al. Factors associated with decision to hospitalize emergency department patients with skin and soft tissue infection. West J Emerg Med 2015;16:89-97.

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