Microbe of the Month: MRSA

Methicillin-resistant Staphylococcus aureus (MRSA) first emerged as a healthcare-associated infection (HAI) in U.S. hospitals in the late 1970s. Since that time, MRSA has become the most common pathogen causing HAIs in healthcare facilities in the United States and throughout the world. Today, MRSA accounts for as many as 50 percent to 70 percent of healthcare-associated S. aureus infections. In the last several years, MRSA has become an emerging community pathogen. The classical emerging community-acquired MRSA (CA-MRSA) usually causes skin and soft tissue infections, while healthcare-associated MRSA (HA-MRSA) causes bloodstream, surgical site, pneumonia or urinary tract infections. CA-MRSA isolates are more susceptible to antimicrobials than HA-MRSA strains. MRSA, by definition, is resistant to the semi-synthetic penicillins such as methicillin, nafcillin and oxacillin, and is therefore resistant to all other beta-lactam antibiotics, including other penicillins, cephalosporins and cephamycins.

Once MRSA becomes endemic within a healthcare facility, it is rarely eliminated and may eventually account for anywhere from 5 percent to 50 percent of all hospital-acquired staphylococcal infections. Public health officials have expressed their concern about the profileration of MRSA due to ease of transmission as well as the limited number of antibiotics available to treat these infections.

Colonized and infected patients are the major reservoirs of MRSA. Colonization occurs when a patient has MRSA but has no clinical signs or symptoms of disease. Infection occurs when MRSA enters a body site and multiplies in tissue, causing clinical manifestations of disease. This is usually evident by fever, a rise in the white blood cell count, or purulent drainage from a wound or body cavity. The distinction between colonization and infection is a clinical one and should be determined by the clinician, not by culture results alone. Colonization often occurs in the nares, axillae, chronic wounds, perineum or around gastrostomy and/or tracheostomy sites. Patients at risk for MRSA colonization are generally debilitated patients who may have prolonged hospitalizations, chronic wounds, or received treatment with multiple antibiotics.

MRSA is usually transmitted from patient-to-patient via the hands of healthcare workers following direct contact with a person who has a purulent lesion or is an asymptomatic carrier. Colonized healthcare workers with dermatitis are especially likely to transmit MRSA to patients.

MRSA has been isolated from environmental surfaces including floors, sinks, work areas, tourniquets used for blood drawing, and blood pressure cuffs. Although MRSA has been isolated from environmental surfaces such as floors and medical equipment, such surfaces are not the most likely source of transmission. However, environmental surfaces should be disinfected routinely to reduce the bacterial load.

Handwashing is the most effective infection control measure to reduce the risk of transmission of MRSA in healthcare settings. Wash hands before patient contact and after touching blood, body fluids, secretions, excretions, and contaminated items, whether or not gloves are worn. Wash hands immediately after gloves are removed, between patient contact, and when otherwise indicated to avoid transfer of microorganisms to other patients or to the environment. Gloves provide a physical barrier between potentially infective material and the healthcare worker's hands and should be used. Healthcare workers should don a gown upon entering the room for any patient placed on Contact Precautions. A gown is necessary when doing direct patient care, or when having contact with the environment or items in the patients room.

Remove the gown before leaving the patients environment; following gown removal, ensure that clothing does not contact potentially contaminated environmental surfaces in order to avoid transfer of microorganisms to other patients or to the environment. Wearing a mask to protect the healthcare provider is based on the assumption that HCWs are more likely to develop nasal colonization while performing certain patient-care activities. Transient nasal carriage has been reported among nurses changing dressings of MRSA patients. However, the value of a mask in reducing transient nasal colonization is not known, but if a patient has a productive cough with MRSA in the sputum, a mask should be worn. Cohorting is advised for patients placed on Contact Precautions if a private room is not available. The patient may be placed in a room with a patient(s) who has MRSA, but no other infection or colonization with a different multiple-antibiotic-resistant organism.

Environmental surfaces should be routinely cleaned with an effective Environmental Protection Agency (EPA)-approved disinfectant detergent, in accordance with the manufacturers instructions. On a daily basis, disinfect bedside equipment such as tables, bed rails, bedside commodes, wheelchairs and other assistive devices. When patient is discharged from the room or no longer has MRSA, terminal cleaning should include changing the bedside curtains.

In March 2007, the Association for Professionals in Infection Control and Epidemiology (APIC) created its Guide to the Elimination of Methicillin- Resistant Staphylococcus aureus (MRSA) Transmission in Hospital Settings. It provides evidence-based practice guidance for the elimination of MRSA transmission in hospital settings. The guide states, Effective efforts to eliminate MRSA transmission are guided by completion of a comprehensive, facilityspecific risk assessment which describes current state and characteristics of the MRSA burden for that facility or setting. Knowledge obtained from the risk assessment drives the development of interventions that result in enhanced compliance with existing facility practices, or in implementation of appropriate additional interventions as described in this guidance document.

The main components of the APIC Guide on the Elimination of MRSA Transmission in Hospital Settings are:

• MRSA risk assessment

• MRSA surveillance programs

• Compliance with basic infection prevention and control strategies, including performing proper hand hygiene, observing Contact

• Precautions, and engaging in thorough environmental and equipment cleaning and decontamination

• Enhanced infection prevention and control strategies (e.g., active surveillance cultures, etc.) when MRSA transmission rates are not decreasing

• Making the business case for eliminating MRSA transmission

• Cultural transformation and change management

• The ancillary topics of antimicrobial stewardship and MRSA decolonization are also aligned with these components.

Reference: Yale-New Haven Infection Control Manual: MRSA.