Skin, Soft Tissue Infections - MRSA
Pearls:
#1. I&D alone is often curative for uncomplicated skin and soft tissue infections with abscesses measuring less than 5 cm.
#2. Eradication of MRSA carrier state is not associated with reduced incidence of clinical MRSA infection
Risk factors for SSTI (Skin and Soft Tissue Infections): IVDU, trauma, burns, CA, DM*, prior SSTI, surgery, bites*.
Treatment depends on patient population/location/degree of CA-MRSA in the community where you practice.
Risk factors for (Community Acquired - Methicillin Resistant Staphylococcal aureas) CA-MRSA SSTI includes:
• athletes, military, prisoners, MSM, pacific islanders, kids, Alaskan and native Americans.
We care about CA-MRSA because of the different susceptibility to antibiotics and different virulence factors. CA-MRSA has been found to carry the genes encoding the Panton-Valentine leukocidin (PVL) exotoxin, which has been associated with SSTIs and necrotizing pneumonia. This cytotoxin causes leukocyte destruction and tissue necrosis, thus facilitating invasion of tissue and abscess formation.
CA MRSA is differentiated from (Healthcare Associated- Methicillin Resistant Staphylococcus aureus) HA-MRSA by fulling all of the following criteria:
• making the diagnosis in the outpatient setting
• no h/o MRSA
• not residing in NH/SNF/hospice
• not on dialysis
• no hospitalization or surgery in past year
• no indwelling catheters
Options for antimicrobial treatment of CA MRSA SSTI:
• clindamycin 300-600mg q6-8
• bactrim DS 2 tabs bid
• linezolid 600 bid
• doxycycline 100mg bid
• rifampin as an adjunct, rarely
I&D is all that is needed (to prevent treatment failure) if uncomplicated, regardless of whether the abscess is MRSA or not. [Am Emer MEd April 29 2009] However, a recent study looking at use of TMP-SMX versus placebo after I&D showed decrease recurrence at 30days (secondary end-point). [Ann Emerg Med. 2010] 20346539.
Steps to I&D:
Drain first by cleansing the area with betadine, then inject lidocaine into the abscess to numb the area, and finally using an #11 scalpel make an incision in parallel with the skin folds. When surgical drainage is performed, there is no difference in clinical outcomes between wound irrigation with tap water versus sterile water. The wound is packed and you should see the patient back in a couple of days for a wound check. This can be done in your clinic if you have the supplies available. Always tell the patient reasons to return to clinic.
Culture?
It is helpful to culture the abscess from the epi standpoint so that we know how much MRSA is around, and in case there is concominant cellulitis and you wish to direct antibiotics, or if there is treatment failure.
The following study addressed the question of whether we should be using empiric beta-lactam antibiotics for SSTI given era of CA-MRSA, and found that even with high rates of CA-MRSA, I&D alone is effective. (Abstract below)
"Empirical use of beta-lactam antibiotics, the preferred agents for treating uncomplicated skin and soft tissue infections, may no longer be appropriate for these infections because of the increasing prevalence of community strains of methicillin-resistant Staphylococcus aureus (MRSA). Retrospective studies, however, suggest that outcomes are good even when beta-lactams are used. We conducted a randomized, double-blind trial of 166 outpatient subjects comparing placebo to cephalexin at 500 mg orally four times for 7 days after incision and drainage of skin and soft tissue abscesses. The primary outcome was clinical cure or failure 7 days after incision and drainage. S. aureus was isolated from 70.4% of abscess cultures. Of the isolates tested 87.8% were MRSA, 93% of which were positive for Panton-Valentine leucocidin genes. Clinical cure rates were 90.5% (95% confidence interval, 0.82 to 0.96) in the 84 placebo recipients and 84.1% (95% confidence interval, 0.74 to 0.91) in the 82 cephalexin recipients (difference in the two proportions, 0.0006; 95% confidence interval, –0.0461 to 0.0472; P = 0.25). The 90.5% cure rate observed in the placebo arm and 84.1% cure rate observed in the cephalexin arm provide strong evidence that antibiotics may be unnecessary after surgical drainage of uncomplicated skin and soft tissue abscesses caused by community strains of MRSA."
[Antimicrobial Agents and Chemotherapy, November 2007, p. 4044-4048, Vol. 51, No. 11]
17846141
(Katharine Cheung MD, 7/22/10)