Methicillin Resistant Staphylococcus Aureus Staphylococcus aureus is an important and common pathogen in humans. It is found in the nose or on the skin of many healthy, asymptomatic persons (i. e. , carriers) and can cause infections with clinical manifestations ranging from pustules to sepsis and death. Most transmission occurs through the contaminated hands of a person infected with or carrying S. aureus. MRSA infections frequently are encountered in health-care settings (Lowy, 1998). A common cause of blood-stream infections, pneumonia, endocarditits, skin and soft tissue infections, and bone and joint infections, S. ureus infection is often associated with significant morbidity and mortality. S. aureus is well adapted to the human body, capable of spreading from person to person, hiding in intracellular compartments and inducing various forms of human disease. During infection the bacterial cells produce a large variety of virulence factors, among which, for instance, are molecules that interfere with the chemotaxis of neutrophils to the site of infection. Adding to the complexity of the infectious process is the fact that the host also responds with a variety of immunological defenses, sometimes producing a certain degree of resistance to infection.
Many healthcare and clinical professionals assume that MSRA is more virulent than its predecessor; however, in control studies, no clear difference has been seen in types of infections, infection severity, and infection-associated mortality caused by MRSA and MSSA (Bradley, 1992). Although not more virulent than MSSA, MRSA infections are significantly more difficult and costly to treat. Treatment generally requires IV antibiotics that are associated with the possibility of increased potential for adverse events compared to those treatable with oral antibiotics and often create the need to move a patient to an acute-care facility.
S. aureus has remained among the top three clinically important pathogens over the past few decades, and a particular worry has been the rise of methicillin resistant strains. In addition to the fact that the organism is not yet completely understood, clinicians worry due to its acquisition of resistance to antibiotics, and how that contributes to its pathoclinical potential. Methicillin resistant S aureus (MRSA) emerged rapidly after the introduction of the antibiotic, with the primary cause of the spread of the MRSA bacteria through clonal dissemination.
Although the gene inducing the resistance has been discovered in various genetic backgrounds, colonisation and infection were mainly caused by rapid spread, sometimes even between continents, of relatively small numbers of epidemic bacterial strains (Lowy, 2000). Since the 1960s, treatment of these infections has become more difficult because S. aureus has progressively acquired resistance to previously effective antimicrobial agents. In 1999, 2,538 (53. 5%) of 4,744 intensive care unit patients with hospital-acquired S. aureus-associated infection had MRSA (Center for Disease Control, 2001).
There has been an increasing prevalence of MRSA as a cause of infections in institutional settings, but there is less information about an increasing role of this pathogen in community-acquired infections. Lending to the confusion is that studies in one center may not necessarily reflect patterns of causative organisms and antimicrobial susceptibility elsewhere. Results from antimicrobial susceptibility testing show resistance of S aureus to penicillin has decreased over the past two decades, while resistance to erythromycin increased from 1980 to 1986 and has remained relatively unchanged since (Guttman, 2001).
Risk factors for infection with MRSA in health-care settings include prolonged hospital stay, exposure to multiple or prolonged broad-spectrum antimicrobial therapy, stay in an intensive care or burn unit, proximity to patients colonized or infected with MRSA, use of invasive devices, surgical procedures, underlying illnesses, and MRSA nasal carriage (Herwaldt, 1999). The success of attempts to maintain microbiological hygiene depends heavily on antibiotic use in individual institutions.
Studies have shown that the rate at which MRSA colonizes and infects patients is significantly correlated with the amount and nature of the antibiotics prescribed in clinics (van Belkum, 2001). Cookson (2002) wrote that although community-onset MRSA infections have been reported recently, little is known about their epidemiology or prevalence of carriage. Community outbreaks have occurred among injection-drug users; aboriginals in Canada, New Zealand, and Australia; Native Americans/Alaska Natives in the United States; and players of close-contact sports.
Reported most commonly have been uncomplicated skin infections; however, community-acquired MRSA infections can be severe In his article, Cookson refers to a Center for Disease Control report of a 1999 outbreak of community-acquired MRSA in which four children in Minnesota and North Dakota died (Center for Disease Control, 1999). Disease transmission can occur easily among inmates at correctional facilities, where skin or soft tissue infections are recognized problems. Close contact among inmates may place them at increased risk for transmission of skin-colonizing or skin-infecting organisms.
To prevent skin disease, all inmates should practice good personal hygiene, including daily showers, should avoid touching wounds or drainage of others and should have access to sinks and plain soap. Personnel that provide wound care for inmates should follow standard precautions including that their hands should be washed with soap as soon as possible after touching wounds or dressings (Beck, 2000). Only recently has the magnitude of symptomatic MRSA infection in older patients living in long term care facilities been identified and documented.
Approximately 2. 5 million Americans reside in LTCFs, and more than 1 million who turned 65 in 1990 are expected to live in a LTCF before they die (Kempner and Murtaugh, 1991, cited in McNeil et al 2002). The number of such facilities reporting asymptomatic colonization or infection of residents with MRSA has been steadily increasing since the late 1980s (Strausbaugh, et. al. , 1996). The factors and rates of colonization vary by geographic location; facility size, prevalence of MRSA in referring institutions; severity of illness of the patient population and nstitutional infection control practices (McNeil, Mody and Bradley, 2002). Concerns over the potential of MRSA into LTCFs from the acute care settings have prompted many nursing homes to refuse patients known to be colonized with MRSA, and they actively screen high-risk, high-probability patients upon arrival. Residents found to be colonized after admission are frequently isolated with other colonized patients or placed under strict contact precautions. These actions may be justifiable, but they place undue hardship on both the staff and the patients of LTCFs.
Patients may be long-term residents of the facility, or may even live there permanently – policies that restrict their movement reduce their quality of life and make rehabilitation intervention difficult. MRSA colonization occurs more frequently in older patients with recognized risk factors and in patients who are debilitated – factors which suggest that it may be a ‘marker’ for increased severity of illnesses from other causes (Bradley, 1991). Comorbidity and overall severity of illness appear to be more important predictors of MRSA infection than other factors alone among those who are colonized.
The risk of MRSA has been shown to be greater in the presence of diabetes mellitus or peripheral vascular disease. MRSA infection may also result from invasive interventions associated with such diseases, such as surgical procedures and dialysis. The issue of control measures are controversial. Few LTCFs have the laboratories or infection control personnel necessary, nor the financial or bed resources necessary to maintain strict contact isolation of colonized residents. Routine infection control strategies in the absence of epidemic infection rarely require measures beyond standard precautions recommended for the care of all patients.
Emphasis should be on hand washing and the use of gloves when exposure to body fluids or non-intact skin is probable, and on the use of gowns when soiling of healthcare workers’ clothing with body fluids is possible. Infection control measures should be based upon the specific venue and directed at preventing a costly, difficult to treat, symptomatic infection with MRSA. Early consultation following the discovery of any increase in the number of infections over the baseline rate should prompt initiation of more aggressive control measures and the identification of residents or staff who may be spreading the outbreak strain.
The ongoing education of personnel in the above-described situations to minimize the risk factors is the most important preventative of all. References Beck, A. J. “Bureau of Justice Statistics Bulletin, Prisoners in 1999. ” Washington, DC: US Department of Justice, Office of Justice Programs, Bureau of Justice Statistics, 2000:16. Bradley, S. F. “Staphylococcus aureus infections and antibiotic resistance in older adults. ” Clinical Journal of Infections Disease 2002; 34(2); 211-6. Bradley, S. F. , Terpenning, M. S. , Ramsey, M. A. , et al. Methicillin-resistant Staphylococcus aureus: Colonization and Infection in a Long-term Facility. Annal of Internal Medicine 1991; 115:417-22. CDC. “Four Pediatric Deaths from Community-acquired Methicillin-Resistant Staphylococcus Aureus–Minnesota and North Dakota, 1997-1999. ” MMWR 1999;48:707-10. CDC. Semiannual report: aggregated data from the National Nosocomial Infections Surveillance system. Available at . Accessed October 2002. Cookson B. D. Methicillin-resistant Staphylococcus aureus in the community: new battle. fronts, or are the battles lost?
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