Methicillin-resistant Staphylococcus aureus (MRSA)

Methicillin-resistant Staphylococcus aureus (MRSA)

Evidence Levels: A Double-blind study B Clinical trial ≥ 20 subjects C Clinical trial < 20 subjects D Series ≥ 5 subjects E Anecdotal case reports

Management strategy

Healthcare-type strains of methicillin-resistant Staphylococcus aureus (MRSA) are associated with sepsis and are common colonists of chronic wounds, where debridement is typically the best strategy. Community-type MRSA infections typically present as an abscess or furunculosis. The most important intervention for an abscess remains surgical drainage. Purulent material can reform rapidly, so a punch or cruciate incision is advised, as it tends to remain open longer to allow adequate drainage. A curette is used to probe the wound and ensure that all pockets of purulent material have been adequately drained. Irrigation can be helpful, but packing is discouraged as purulent material often reforms behind the packing material. Evidence suggests that antibiotics are often unnecessary if an abscess is adequately drained. There are obvious reasons to avoid antibiotics when they are not needed, including the risk of Stevens–Johnson syndrome, antibiotic associated diarrhea, and selection of resistant strains.

Patients with significant surrounding cellulitis, refractory infection or systemic manifestations may require antibiotic therapy. Most community-associated (CA)-MRSA strains are sensitive to trimethoprim–sulfamethoxazole. Most strains are also sensitive to doxycycline and minocycline, but doxycycline does not penetrate well into the nares. Clindamycin resistance is emerging in many communities. For serious infections, therapy should be guided by culture and sensitivity. Vancomycin, linezolid, dalbavancin, telavancin, and daptomycin are often effective. Rifampin improves intracellular killing of bacteria by vancomycin. Quinupristin–dalfopristin and tigecycline may also be effective, but quinupristin–dalfopristin, like daptomycin, may not penetrate reliably into pulmonary tissue and tigecycline has a significant incidence of nausea. Ceptobiprole and oritavancin appear promising.

Spread occurs through skin-to-skin contact and via fomites. Decolonization may be indicated for prevention of recurrence or prevention of serious invasive disease in close contacts. The most effective decolonization regimens address the nares, intertriginous and anogenital sites, as well as eczematous skin. In some patients, gut colonization may also be an issue.

Specific investigations

Cultures should be obtained from the contents of purulent infections and resistant infections. New molecular diagnostic tests are being developed to screen for MRSA and identify genes associated with resistance.

The prevalence, genotype and antimicrobial susceptibility of high- and low-level mupirocin resistant methicillin-resistant Staphylococcus aureus.

Park SY, Kim SM, Park SD. Ann Dermatol 2012; 24: 32–8.

In this study, 27 of 193 (14.1%) MRSA isolates were resistant to mupirocin. It was noteworthy that high-level mupirocin resistance was common among hospital isolates. These isolates were susceptible to vancomycin and rifampin, but resistant to ciprofloxacin, clindamycin and tetracycline.

Mupirocin-resistant isolates could transfer this resistance to other bacteria emphasizing the importance of using topical antibiotics judiciously.

Mupirocin resistance in Staphylococcus aureus causing recurrent skin and soft tissue infections in children.

McNeil JC, Hulten KG, Kaplan SL, Mason EO. Antimicrob Agents Chemother 2011; 55: 2431–3.

Staphylococcal resistance to mupirocin is often related to acquisition of isoleucyl-tRNA synthetase encoded on the plasmid gene mupA. A study at Texas Children’s Hospital demonstrated that 20 of 136 isolates were resistant to mupirocin (14.7%). Fifteen of the resistant isolates (11%) carried mupA. Seven of the 20 mupirocin-resistant isolates also demonstrated clindamycin resistance.

Mupirocin resistance continues to spread. In this study, the gene was more common among methicillin-susceptible S. aureus isolates (21.4% vs 8.3%; p = 0.03).

Clinical importance of purulence in methicillin-resistant Staphylococcus aureus skin and soft tissue infections.

Crawford SE, David MZ, Glikman D, King KJ, Boyle-Vavra S, Daum RS. J Am Board Fam Med 2009; 22: 647–54.

In a study of 262 patients with purulent skin and soft tissue infections performed at the University of Chicago Medical Center, 253 (97%) contained the staphylococcal chromosomal cassette mec (SCCmec) IV and 245 (94%) contained Panton-Valentine leukocidin (pvl) genes, both common characteristics of community-associated MRSA strains. 231 of the isolated strains (88%) were susceptible to clindamycin. In contrast, among the 87 isolates from non-purulent infections, only 44% were susceptible to clindamycin.

These data suggest that, at least in Chicago, purulent MRSA infections are more likely to be caused by clindamycin-susceptible isolates.

Susceptibility testing and resistance phenotype detection in Staphylococcus aureus strains isolated from patients with atopic dermatitis, with apparent and recurrent skin colonization.

Kedzierska A, Kapiūska-Mrowiecka M, Czubak-Macugowska M, Wójcik K, Kedzierska J. Br J Dermatol 2008; 159: 1290–9.

In a study of 87 patients with mild to severe atopic dermatitis, nearly 35% of S. aureus strains from lesional skin demonstrated different antimicrobial sensitivity patterns from strains from non-lesional skin of the same patient.

Cultures from different sites of atopic skin often demonstrate discordant antibiotic sensitivities. This suggests that the colonizing and infecting strains may be different and fresh cultures may be needed when treating infections.

Cost-analysis of PCR-guided pre-emptive antibiotic treatment of Staphylococcus aureus infections: an analytic decision model.

Hübner C, Hübner NO, Kramer A, Fleßa S. Eur J Clin Microbiol Infect Dis 2012; 31: 3065–72.

A decision analytic cost model performed by a group of German investigators concluded that at the current MRSA prevalence of 24.5 %, PCR-guided treatment regimens are cost-efficient compared with empiric treatment. The greatest impact was the cost of hospitalization.

Rapid polymerase chain reaction (PCR)-based screening appears to be a cost-efficient tool to optimize pre-emptive antibiotic therapy of methicillin-resistant and methicillin-sensitive Staphylococcus aureus infections.

High vancomycin minimum inhibitory concentration is a predictor of mortality in methicillin-resistant Staphylococcus aureus bacteremia.

Wi YM, Kim JM, Joo EJ, Ha YE, Kang CI, Ko KS, Chung DR, Song JH, Peck KR. Int J Antimicrob Agents 2012; 40: 108–13.

A retrospective cohort study of 137 patients with MRSA bacteremia demonstrated a 30-day cumulative survival of 53.8% for patients infected with isolates having a MIC ≥ 1 µg/mL and 79.8% for patients infected with isolates having a MIC <1 µg/mL (log-rank test, p = 0.026).

Although data have been mixed, this study suggests early consideration of an alternative agent in seriously ill patients with MRSA bacteremia whose isolate demonstrates high vancomycin MICs.

Is methicillin-resistant Staphylococcus aureus involved in community acquired skin and soft tissue infections? Experience from a tertiary care centre in Mumbai.

Phakade RS, Nataraj G, Kuyare SK, Khopkar US, Mehta PR. J Postgrad Med 2012; 58: 3–7.

Methicillin-susceptible S. aureus remains the predominant pathogen in community-acquired skin infections.

Cultures remain important, but β-lactam drugs are still reasonable first choices for empiric treatment of skin infections. The D test should be carried out routinely in MRSA stains to detect inducible clindamycin resistance.

First-line therapy

Treatment of MRSA abscesses
Surgical drainage alone	B
Surgical drainage plus
– trimethoprim–sulfamethoxazole	B
– minocycline	B
– doxycycline	B
– clindamycin	B
Eradication of colonization: nares
Mupirocin	B
Tea tree oil	B
Eradication of colonization: skin
Bleach baths	D
Chlorhexidine	B
Triclosan	B
Tea tree oil soap	B
Undecylenamidopropyltrimonium methosulphate/phenoxyethanol	C
Octenidine dihydrochloride	C

Randomized controlled trial of cephalexin versus clindamycin for uncomplicated pediatric skin infections.

Chen AE, Carroll KC, Diener-West M, Ross T, Ordun J, Goldstein MA, et al. Pediatrics 2011; 127: e573–80.

This was a comparison of clindamycin and cephalexin for the treatment of uncomplicated skin and soft tissue infections caused predominantly by CA-MRSA. Of the 200 enrolled patients, 69% demonstrated MRSA on wound cultures. Spontaneous drainage or a drainage procedure occurred in 97% of subjects. There is no significant difference between cephalexin and clindamycin in this study.

The data presented here are similar to previous data. The treatment for an uncomplicated abscess remains drainage and the use of an antibiotic has little effect on outcome.

Dose of trimethoprim–sulfamethoxazole to treat skin and skin structure infections caused by methicillin-resistant Staphylococcus aureus.

Cadena J, Nair S, Henao-Martinez AF, Jorgensen JH, Patterson JE, Sreeramoju PV. Antimicrob Agents Chemother 2011; 55: 5430–2.

A prospective case-control study compared high-dose TMP/SMX (320 mg/L, 600 mg twice daily) for 7 to 15 days with the standard dose of TMP/SMX (160 mg/800 mg twice daily). The two groups had a similar rate of clinical resolution.

The primary intervention for an MRSA abscess remains drainage. When antibiotics are necessary, standard doses of TMP/SMX typically suffice. Sulfa MICs are usually excellent for MRSA isolates. As higher doses can cause nausea, standard doses are generally appropriate.

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Tags: Treatment of Skin Disease Comprehensive Therapeutic Strategies

Aug 7, 2016 | Posted by admin in Dermatology | Comments Off

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