Community Acquired MRSA Skin and Soft Tissue Infections
Last updated: 03/31/2006
The proportion of Staphylococcus aureus infections caused by methicillin resistant strains has been on the rise for the past decade. Recently methacillin resistant staphylococcus aureus (MRSA) strains causing infections in the community have emerged that are genetically distinct from previously known strains. It is now estimated that forty-two percent of all MRSA infections are caused by these community acquired strains. Outbreaks involving these new strains have occurred all over the world.
The populations involved in the community acquired MRSA (CA-MRSA) outbreaks do not have the usual risk factors associated with MRSA infections such as hospitalization, long term care residence, indwelling catheters, diabetes or hemodialysis. In fact, most patients are young and otherwise healthy. Risk factors for CA-MRSA identified from retrospective analysis include incarceration, participation in close contact sports, crowded living conditions, intravenous drug use, poor hygiene and low socioeconomic status.
CA-MRSA is most likely to cause skin and soft tissue infections (SSI), though other more serious infections have been reported. These include necrotizing pneumonia, sepsis and septic shock, toxic shock-like syndrome, infective endocarditis and urinary tract infections. Typical presentations of SSI include cellulitis and single solitary abscesses or lesions, especially furunculosis and folliculitis. These infections are often mistaken for brown recluse spider bites. The patient may report a history of recurring skin lesions. Cultures of nasal swabs often reveal colonization of the nares with MRSA.
CA-MRSA strains are resistant to ß-lactam antibiotics but are not usually multi-drug resistant. Thus several options exist for the management and treatment of these infections. The Infectious Diseases Society of America has developed guidelines for the management of SSI, including those caused by CA-MRSA. First line options for mild, uncomplicated infections include sulfamethoxazole-trimethoprim, clindamycin and doxycycline. Clindamycin should be used cautiously in geographical areas where inducible resistance to clindamycin is common. For more serious, complicated infections, inpatient treatment with vancomycin or linezolid is recommended. Other antimicrobials typically active against CA-MRSA may include rifampin, levofloxacin, ciprofloxacin, erythromycin, quinupristin-dalfopristin, daptomycin and tigecycline.
Determining proper drug therapy depends on accurately diagnosing the organism causing the infection. Cultures and susceptibility tests are the best way to definitively diagnose the infection, but often are not finalized for at least forty-eight hours. A thorough history and physical exam is necessary to determine which, if any, risk factors are present. Initial drug therapy can begin based on the presence or absence of risk factors, along with instructions for the patient to return in forty-eight to seventy-two hours if the skin lesions do not improve or they worsen. For patients presenting with recurring skin lesions, culture of the nares may be considered to look for nasal colonization. Mupirocin ointment may be applied to the nares to eliminate colonization.
The optimal duration of therapy is unknown; most infections may resolve after ten to twenty-one days of therapy. Patients who do not improve during this time should be reevaluated for other pathogens or disease states. Severe CA-MRSA infections requiring inpatient therapy may require longer treatment.