Infections with methicillin-resistant Staphylococcus aureus have become increasingly prevalent in community and health care settings since the first clinical isolate was described in 1961. There were nearly 100,000 cases of invasive MRSA infections in the United States in 2005. The Infectious Diseases Society of America recently published a guideline to aid in the clinical management of MRSA infections.
Conclusions
MRSA causes infections in ambulatory and inpatient settings. The epidemiology of MRSA has become complex, as strains that were historically associated with community or health care facilities have commingled and emerged in both types of health care settings. These infections can range from simple cutaneous abscesses to serious invasive infections.
The particular clinical scenario, local resistance pattern, and epidemiology of MRSA in a community are all relevant in making decisions about the appropriate treatment of an individual patient with MRSA infection.
Bacteremia is present in approximately 75% of cases of invasive MRSA infection.
Vancomycin is the standard parenteral therapy for MRSA infections; however, its slow bactericidal activity, variable tissue penetration (especially into bone, lung lining, and cerebrospinal fluid), and the emergence of increasing resistance all pose challenges to its use.
Implementation
Incision with drainage is the primary treatment for skin abscesses; the addition of antibiotic therapy has no clear role in the absence of additional complicating factors such as severe or extensive disease, signs of systemic illness, rapid progression, immune compromise, patients at the extremes of age, an abscess likely not to be completely drained, and/or lack of response to drainage alone.
Outpatients with purulent cellulitis in the absence of a drainable abscess should be treated empirically for MRSA pending culture.
Cellulitis without purulent drainage or an abscess in outpatients should be treated empirically for infection due to beta-hemolytic streptococci. MRSA should be considered in those who have signs of systemic toxicity or in those who do not respond to antistreptococcal treatment.
Empirical antimicrobials for outpatient MRSA skin infections include clindamycin, trimethoprim-sulfa, a tetracycline, and linezolid. Although linezolid is significantly more costly, there is no clinical trial documenting superior cure rates with its use. Rifampin is not recommended for MRSA skin infections.
Hospitalized patients with complicated soft-tissue infections should be treated with surgical debridement and broad-spectrum antimicrobials, including empirical antimicrobials for MRSA, pending culture data.
In addition to appropriate antibiotic treatment, adults with MRSA bacteremia should have echocardiographic evaluation for endocarditis, clinical assessment to look for other foci of infection, and repeat blood cultures 2-4 days following the initial set to assess for clearance of bacteremia.
Transesophageal is preferred over transthoracic echocardiography for endocarditis assessment.
Vancomycin or daptomycin for a minimum of 2 weeks is recommended for treatment of uncomplicated bacteremia. Complicated bacteremia and endocarditis should be treated parenterally for at least 4-6 weeks, in addition to debridement of any septic foci of infection. The addition of gentamicin or rifampin is not recommended in MRSA bacteremia or native valve endocarditis treatment. Prosthetic valve endocarditis should be treated with the combination of vancomycin, gentamicin, and rifampin; early evaluation for valve replacement is recommended.
Empirical treatment for severe community-acquired pneumonia should include MRSA coverage, pending culture results. Daptomycin should not be used for pneumonia.
MRSA pneumonia, whether of community or health care facility origin, may be treated with IV vancomycin, linezolid [oral/IV] or clindamycin [oral/IV] in susceptible patients; antimicrobials should be continued for 7-21 days, depending on the patient’s response.
MRI with gadolinium contrast is the best imaging modality for the evaluation of osteomyelitis.
Surgical debridement and drainage of infected tissues are mainstays of therapy for bone and joint infections. Concomitant antibiotic treatment is recommended for a minimum of 8 weeks for osteomyelitis, and for 3-4 weeks for native joint septic arthritis. The specifics of management of acute prosthetic joint and spinal implant infection differ from treatment for patients who have had their implants for a longer duration; regardless, most require prolonged antimicrobial therapy and debridement.
IV vancomycin is recommended for the treatment of MRSA infections of the central nervous system, although linezolid and IV trimethoprim/sulfa are alternatives.
Shunt removal (with replacement only after cerebrospinal fluid cultures remain sterile) and antimicrobials are recommended for CNS shunt infection. Brain abscesses, subdural empyema, spinal epidural abscesses, and septic thrombi of the cavernous and dural venous sinuses should be surgically debrided if possible.
IV vancomycin should be dosed at 15-20 mg/kg (maximum dose, 2 g) of actual body weight every 8-12 hours in patients with normal renal function. Vancomycin trough levels should be monitored before the fourth or fifth dose after initiation and dosing changes. Trough concentrations of 15-20 mcg/mL are recommended when vancomycin is used to treat serious MRSA infections.