Introduction to MRSA
Methicillin-resistant Staphylococcus aureus (MRSA) was first reported decades ago in the United States and was related to exposures in the healthcare system. These staphylococcal (Staph) bacteria are resistant to beta-lactam antibiotics, including methicillin, oxacillin, penicillin, and amoxicillin.
CA-MRSA vs HA-MRSA
Over the past 10 years, MRSA has emerged in the community with clinical, epidemiologic, and bacteriologic characteristics distinct from healthcare-associated MRSA (HA-MRSA). Community-associated MRSA (CA-MRSA) has its onset in the community in an individual lacking the established MRSA risk factors, such as a recent hospitalization, surgery, residence in a long-term care facility, receipt of dialysis, or the presence of an invasive medical device. Additionally, there is molecular evidence that CA-MRSA strains evolved spontaneously rather than from migration out of hospitals. The methicillin resistance is coded in the chromosomemec type IV, which had not been characteristic of healthcare-associated strains. Furthermore, CA-MRSA produces several toxins that aren't commonly found in the nosocomial strains, such as the Panton-Valentine leukocidin, which causes leukocyte destruction and tissue necrosis. The MRSA strain, USA 300, is most associated with CA-MRSA.
CA-MRSA: Clinical Presentation and Disease Burden
CA-MRSA most often presents as a skin or soft-tissue infection, such as a boil, pimple, or abscess, in an otherwise healthy person. Patients frequently recall a "spider bite." The lesions are often red, swollen, and painful and may have pus or a discharge. They are commonly found in cuts and scrapes and in hairy areas of the body, such as the back of the neck, groin, buttocks, armpits, and the inner thigh. By 2007, CA-MRSA was the most frequent cause of skin and soft-tissue infections seen in emergency departments in the United States.
Although most MRSA cases are skin and soft-tissue infections, some are more serious with septicemia and pneumonia. In 1999, four children in Minnesota and North Dakota were reported to have died from fulminant CA-MRSA infections. It was reported in 2005 that previously healthy adolescents without any predisposing risk factors presented more frequently with severe Staph infections (mostly the USA 300 strain) since 2002. CA-MRSA has been associated with necrotizing pneumonia and empyema; sepsis syndrome; musculoskeletal infections, such as pyomyositis and osteomyelitis; necrotizing fasciitis; purpura fulminans; and disseminated infection with septic emboli. A recent editorial speculated that the number of deaths from MRSA would exceed the total number of deaths attributable to HIV/AIDS in the United States in 2005.
CA-MRSA: Disease Transmission and Risk Factors
CA-MRSA infections can be spread by contact with infected skin or personal items, such as towels, bandages, or razors, that have been in contact with infected skin. It is more likely to spread in places where there is close contact, such as locker rooms or correctional facilities. The bacteria get into the skin through scrapes or cuts or small openings in the skin, particularly around hair follicles. Investigations have shown transmission through the sharing of common objects, such as athletic equipment, towels, benches, and personal items contaminated with MRSA. Outbreaks have been reported in football, wrestling, rugby, soccer, fencing, canoeing, and groups with close person-to-person contact, such as day care center attendees, jail and prison inmates, and the military. There have also been CA-MRSA cases in tattoo recipients. A study conducted at 3 emerging infection program sites by the US Centers for Disease Control and Prevention (CDC) found between 18.0 and 25.7 cases of CA-MRSA per 100,000 population, with 75% being skin and soft-tissue infections.
Risk factors include:
Close skin-to-skin contact;
Openings in the skin, such as cuts and scrapes;
Contaminated items and surfaces, such as soap and towels;
Crowded living conditions;
Poor hygiene, skipping showers before using communal whirlpools;
Improper wound care; and
Poor hand hygiene -- lack of access to handwashing facilities.
CA-MRSA: Diagnosis and Treatment
The criteria for the diagnosis of CA-MRSA are that the diagnosis is made by culture in an outpatient setting or within 48 hours of hospital admission; there is no medical history of MRSA infection or colonization; there is no history in the past year of hospitalization, admission to a nursing home, admission to a skilled nursing facility or hospice, dialysis, or surgery; and there are no permanent indwelling catheters or medical devices that pass though the skin. The treatment of skin and soft-tissue infections includes incision and drainage and antibiotic therapy, if indicated, on the basis of the susceptibility profile of the culture.
CA-MRSA: Prevention and Control
There are several strategies that healthcare providers should take to prevent and control CA-MRSA infections. Clinicians should culture suspect lesions and provide targeted antimicrobial and surgical therapy. Healthcare workers must maintain the appropriate infection control precautions during wound care of patients with skin infections. Patients and families should be provided simple instructions to prevent the transmission of skin infections to family members or other contacts with education on appropriate wound management, hand and body hygiene, and eliminating the sharing of potentially contaminated items. The CDC convened a meeting of experts in March 2006, and issued the following recommendations for controlling CA-MRSA:
Keep draining wounds covered with clean, dry bandages.
Stress good hand hygiene; wash regularly with soap and water or alcohol-based gel if not visibly soiled. Always wash hands immediately after any contact with infected skin or items in direct contact with drainage.
Bathe regularly.
Don't share items that may be contaminated from a wound, such as towels, clothing, bedding, bar soap, razors, and athletic equipment.
Launder clothing that comes into contact with the wound and dry thoroughly.
No participation in athletic events and other activities with skin contact with other people unless the wound can be kept covered with a clean, dry bandage.
Clean equipment and other environmental surfaces if multiple people have skin contact with it. MRSA can survive on some surfaces for a long time (hours to months) depending on the temperature; humidity; the amount present; the type of surface, such as those that are porous; and if nutrients are present. Effective disinfectants registered with the US Environmental Protection Agency (EPA) are available at retail stores and should be used according to their directions. Contact time is critical.
There are not enough data available to assess the association between MRSA colonization and infection in the community. MRSA is frequently colonized in the nose. Colonization can also occur in the pharynx, axilla, rectum, and perineum. The CDC reports that 25% to 30% of the US population are colonized with Staph at any time, but that only about 1% is colonized with MRSA. Colonization may be important in the development and transmission of infection and the persistence or reappearance of colonization after the use of decolonization agents. A combination of topical and systemic antimicrobial agents and antiseptic body washes have been used. Mupirocin used intranasally has been effective in the short term, but recolonization has been common.