Methicillin-resistant Staphylococcus aureus (MRSA) was first described in 1961, and outbreaks were first reported in the early 1960s.1 Although approximately 30% of the population is colonized with Staphylococcus bacteria, only about 1% of the population is colonized with MRSA. The prevalence of MRSA has increased worldwide as both a community-associated (CA-MRSA) and a hospital-acquired (HA-MRSA) pathogen.
DISTINGUISHING CAUSE
OF INFECTION
CDC criteria for distinguishing CA-MRSA include (1) diagnosis is made in the outpatient setting or via positive culture within 48 hours after hospital admission; (2) no medical history of MRSA infection or colonization; (3) no medical history of surgery, dialysis, or hospitalization or admission to a nursing home, skilled nursing facility, or hospice in the past year; (4) no presence of an indwelling catheter or medical device that passes through the skin into the body.2
Although MRSA infections are primarily hospital acquired, patients infected with community-associated strains of MRSA are increasingly being seen in hospital settings, blurring the distinction between CA-MRSA and HA-MRSA. Patients may be colonized in the community and the infection manifests in the hospital setting.3
TREATMENT OF CA-MRSA
Patients with fluctuant or purulent infection should undergo incision and drainage (I&D) with culture and susceptibility testing. Patients with large abscesses and/or signs of systemic infection should be managed with I&D and antimicrobial therapy. Oral antibiotics are not needed if the abscess is smaller than 5 cm and there is no evidence of systemic involvement.
Oral antibiotic regimens are clindamycin 300 to 450 mg every 6 to 8 hours for 1 to 2 weeks; trimethoprim-sulfamethoxazole, two double-strength tablets twice a day for 1 to 2 weeks; doxycycline or minocycline 100 mg twice a day for 1 to 2 weeks; and rifampin 300 mg, twice a day for 5 days (adults) or 10 to 20 mg/kg/d in two doses, not to exceed 600 mg/d, for 5 days (children). Rifampin should not be used as monotherapy because resistance can emerge rapidly. Linezolid 600 mg every 12 hours for 10 days may be considered if other treatment regimens fail; close monitoring for myelosuppression is needed.4,5 Patients should be evaluated after 24 to 48 hours of oral antibiotic therapy to verify clinical response.
Parenteral therapy should be considered for patients with extensive soft tissue involvement, fever, or systemic illness or for patients with diabetes or other immunodeficiency. The preferred treatment is vancomycin 30 mg/kg/d IV in two divided doses, not to exceed 2 g/d, for 1 to 2 weeks. Alternatives for patients who fail to respond or cannot tolerate vancomycin are linezolid 600 mg IV every 12 hours for 1 to 2 weeks; daptomycin 4 mg/kg/d IV for 1 to 2 weeks; or tigecycline 100 mg IV once followed by 50 mg IV every 12 hours for 1 to 2 weeks.4,5
TREATMENT OF HA-MRSA
Patients should undergo aggressive debridement of infected skin and deep soft tissue structures, and a determination of adequate peripheral vascular supply should be made.
Patients with HA-MRSA should be treated with oral linezolid 600 mg every 12 hours for 1 to 3 weeks and should be monitored for myelosuppression. If antibiotic treatment may be needed for more than 3 weeks, vancomycin 30 mg/kg/d IV, adjusted as necessary to therapeutic levels, should be started immediately. These patients should also be monitored for nephrotoxicity, ototoxicity, and thrombocytopenia. Patients with renal insufficiency or failure or vancomycin-resistant infection should receive linezolid alone. Osteomyelitis caused by HA-MRSA requires aggressive surgical resection of the infected bone and soft tissue, determination of sufficient peripheral vascular supply, and a 6-week course of IV vancomycin at the above-described dosage; linezolid may be substituted as described above.3 JAAPA
Mary Hewett is an assistant professor in the PA program at the Medical University of South Carolina, Charleston, and the department editor for When the Patient Asks. She has indicated no relationships to disclose relating to the content of this article.
DRUGS MENTIONED
Clindamycin (Cleocin, generics)
Daptomycin (Cubicin)
Doxycycline (Oracea, Vibramycin, generics)
Linezolid (Zyvox)
Minocycline (Dynacin, Minocin, Solodyn, generics)
Rifampin (Rimactane, Rifadin, generics)
Tigecycline (Tygacil)
Trimethoprim-sulfamethoxazole (Bactrim DS, Septra DS, Sulfamethorpim DS, generics)Vancomycin (Vancocin Hydrochloride, generics)
REFERENCES
1. Barber M. Methicillin-resistant staphylococci. J Clin Pathol. 1961;14:385-393.
2. Naimi TS, LeDell KH, Como-Sabetti K, et al. Comparison of community- and health care-associated methicillin-resistant Staphylococcus aureus infection. JAMA 2003;290(22):2976-2984.
3. Klevens RM, Morrison MA, Nadle J, et al; Active Bacterial Core surveillance (ABCs) MRSA Investigators. Invasive methicillin-resistant Staphylococcus aureus infections in the United States. JAMA. 2007;298(15):1763-1771.
4. Daum RS. Clinical practice. Skin and soft tissue infections caused by methicillin-resistant Staphylococcus aureus.
N Engl J Med. 2007;357(4):380-390.
5. Moellering RC Jr. Current treatment options for community-acquired methicillin-resistant Staphylococcus aureus infection. Clin Infect Dis. 2008;46(7):1032-1037.
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