Minimizing Methicillin-resistant Staphylococcus aureus in the Community


Atlanta, Georgia USA


July 19–20, 2004

On July 19–20, 2004, in Atlanta, Georgia, the Centers for Disease Control and Prevention convened a meeting of experts representing academic medicine; local, state, and federal public health; and other federal agencies, including the US Food and Drug Administration, the Federal Bureau of Prisons, and the Department of Defense. The goals of the meeting were to 1) review current knowledge regarding transmission of methicillin-resistant Staphylococcus aureus (MRSA) in the community, 2) discuss strategies for management on the individual patient and community level, and 3) identify areas where additional research is needed. A detailed summary of strategies for the clinical management of MRSA in the community, based on discussions held at this meeting, and in conjunction with additional data available as of January 2006, is available at http://www.cdc.gov/ncidod/dhqp/ar_mrsa_ca_04meeting.html. A detailed summary of potential public health intervention strategies will be published separately.

Before the meeting, participants prepared and distributed reviews of the scientific literature pertaining to the epidemiology, management, and control of MRSA in the community. During the meeting, working discussions were held on 7 topics: 1) definitions and terminology for MRSA in the community, 2) issues in the clinical evaluation and treatment of skin and soft tissue infections (SSTIs) in the era of community-associated MRSA, 3) the role of the individual clinician in identification and management of MRSA clusters, 4) targeting and developing health promotion materials, 5) factors and settings that should prompt a public health response, 6) public health intervention strategies, and 7) clinical laboratory issues.

MRSA has emerged in the community with clinical, epidemiologic, and bacteriologic characteristics distinct from healthcare-associated MRSA (HA-MRSA). Community-associated MRSA (CA-MRSA) refers to an MRSA infection with onset in the community in a person without established MRSA risk factors, such as recent hospitalization, surgery, residence in a long-term care facility, dialysis, or use of invasive medical devices (1). The term CA-MRSA has also been used to refer to MRSA strains with bacteriologic characteristics (e.g., genotypes, antimicrobial drug susceptibility profiles) considered typical of isolates obtained from patients with CA-MRSA infections (2). However, the association initially observed between isolate characteristics and MRSA transmission in the community versus healthcare settings appears to be breaking down. From a clinical management standpoint, awareness of local resistance patterns for pathogens in the differential diagnosis of specific clinical syndromes is more important than categorizing possible MRSA infections as CA-MRSA or HA-MRSA.

Most CA-MRSA infections have been SSTIs, notably abscesses; however, severe and invasive manifestations have also occurred (1). Outbreaks of CA-MRSA have occurred in many settings (e.g., athletic teams, correctional facilities, military training facilities), but most cases occur in persons with no clear link to one of these settings. Anecdotal reports suggest that recurrent SSTIs and clustering of infections within a household are relatively common. The incidence of CA-MRSA infection varies geographically in the United States.

Unlike HA-MRSA isolates, which are usually resistant in vitro to multiple classes of antimicrobial agents, many CA-MRSA isolates are resistant only to β-lactams and macrolides (1). However, resistance to other antimicrobial drug classes, such as fluoroquinolones and tetracyclines, occurs and may be increasing in prevalence (1,3). Most CA-MRSA isolates are susceptible to trimethoprim-sulfamethoxazole, gentamicin, tetracycline, and clindamycin. However, some S. aureus isolates that appear by routine susceptibility testing to be erythromycin-resistant and clindamycin-susceptible can be induced to express resistance to clindamycin in vitro, and this inducible resistance might in some circumstances result in clinical treatment failure (4). Inducible clindamycin resistance can be detected with a specialized laboratory test called a D-zone test (5).

Clinicians should consider MRSA in the differential diagnosis of SSTIs and other syndromes compatible with staphylococcal infection. Clinicians are encouraged to collect specimens from patients with SSTIs and other possible staphylococcal infections for culture and antimicrobial drug susceptibility testing.

Incision and drainage are primary therapy for skin abscesses; for some patients, this procedure may be supplemented with antimicrobial drug therapy. Many antimicrobial agents have been proposed as alternatives to β-lactams when antimicrobial drug therapy is considered clinically indicated for an SSTI and coverage for MRSA is desired (6,7). Each of these agents has advantages and disadvantages, and data are needed from controlled clinical trials to establish optimal regimens. Educating patients on strategies to limit further spread of infection is a critical component of SSTI case management.

The decision for a public health agency to initiate an investigation of MRSA spread in the community should take into account various factors, including the number of cases and extent of clustering in time and space, setting in which transmission occurs, severity of illness among the patients, ongoing transmission among members of the affected cohort, host factors of persons likely to be exposed, and the likelihood that an intervention could be successfully implemented in a given setting. Desirable components of a public health intervention include 1) enhancing surveillance for new or previously unrecognized infections, 2) targeting empiric antimicrobial drug therapy of new infections to the susceptibility pattern of the outbreak strain, 3) educating patients and their close contacts on wound care and wound containment, 4) promoting enhanced personal hygiene and discouraging sharing of personal items, 5) excluding patients with active infections from certain activities if they are unable to contain wound drainage and maintain adequate personal hygiene, and 6) achieving and maintaining a clean environment.

Data from controlled trials are needed to determine the efficacy of strategies to eliminate S. aureus colonization as a means of preventing S. aureus infection in the community. However, recognizing that efficacy data are lacking, administering decolonization regimens may be reasonable if primary measures are unsuccessful at controlling recurrent MRSA infections in an individual patient or if transmission is ongoing in a well-defined cohort. Consultation with an infectious disease specialist may be helpful in these instances.

Additional data from well-designed studies are needed to fully understand the epidemiologic, microbiologic, and pathophysiologic features of CA-MRSA infections and identify optimal prevention and treatment strategies. However, strategies focusing on increased awareness, early detection and appropriate management, enhanced hygiene, and maintenance of a clean environment appear to have been successful at limiting the spread of CA-MRSA.