Skin and soft tissue infections (SSTIs) caused by MRSA (methicillin resistant Staphylococcus aureus) have become increasingly common over the past 15-20 years. Defined by resistance to methicillin with an MIC>= 4mcg/mL, MRSA strains are resistant to all beta-lactam antibiotics except for the newest class of MRSA-active cephalosporins, such as ceftaroline.
Historically, MRSA was primarily a health care-associated pathogen, but in the mid-late 1990s the emergence of so-called community-associated MRSA strains led to a dramatic increase in MRSA infections in otherwise healthy patients. The spectrum of MRSA infections ranges from asymptomatic colonization to SSTIs to more invasive infections such as osteomyelitis, bacteremia and endocarditis. SSTIs are the most common presentation.
The diagnostic challenge
A diagnostic challenge is determining when an SSTI is caused by MRSA. MRSA SSTIs often begin looking like a spider bite and then progress to a pustule or deeper abscess, but these may be indistinguishable from SSTIs caused by MSSA (methicillin-susceptible Staphylococcus aureus) or other pathogens.
A history of MRSA infections in the patient or in family or other close contacts may provide a clue for the etiology. Culture of purulent material from a lesion is optimal in providing a diagnosis.
Read one mother’s story of her child’s experience with MRSA on our Thriving blog.
Incision and drainage (I&D) is the mainstay of treatment of MRSA abscesses and boils. Smaller lesions less than 5 cm may be managed by I&D alone, while antibiotics are recommended for severe or more extensive disease, areas of involvement such as the face which may be difficult to drain, rapid progression, systemic illness or other risk factors such as extremes of age or immunosuppression.
Empiric antibiotic choice depends on several factors, including severity of illness and likelihood of MRSA. For outpatients with an abscess or purulent cellulitis, empiric coverage with trimethoprim-sulfamethoxazole, clindamycin or, for older patients, doxycycline is often used, as many MRSA and MSSA strains are susceptible to those agents.
Recurrent MRSA SSTIs
Recurrent SSTIs due to MRSA can be problematic. Prevention strategies endorsed by the U.S. Centers for Disease Control and Prevention and Infectious Diseases Society of America include focus on personal and environmental hygiene. Patients and parents should be counseled to cover draining wounds, handwash frequently and avoid sharing personal items with others, such as towels and bar soaps. In addition, because of the potential contribution of MRSA colonization to recurrent MRSA infection, decolonization may be advised, usually with daily nasal mupirocin in combination with topical chlorhexidine or bleach baths for a period of five to 10 days. Occasionally, an oral antibiotic course with a first-line antibiotic combined with rifampin, may be used in combination with topical decolonization attempts.
Thomas Sandora, MD, MPH, is Boston Children’s Hospital’s medical director for infection control and hospital epidemiologist, as well as an associate professor of pediatrics at Harvard Medical School.
Patients with recurrent infections may be referred to the Boston Children’s Hospital Division of Infectious Diseases for evaluation, counseling and education about prevention of recurrent MRSA SSTIs.