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Community-Acquired MRSA Infection |
Methicillin-resistant Staphylococcus aureus (MRSA) was once considered a strictly nosocomial pathogen. Over the past decade, however, MRSA has emerged as a prominent cause of community-associated infections in both adults and children. Although community-associated MRSA strains occasionally cause severe invasive infections, they are most frequently isolated from patients with skin and soft tissue infections.1 Furunculosis (“boils”) is the most frequently reported manifestation of community-associated MRSA skin infection, but impetigo, pustulosis, cellulitis (Figure 1), and locally invasive abscesses have also been described.2
The tendency of staphylococcal skin infections to recur is well recognized. Data on the frequency of recurrence, however, are sparse. In a study of 69 children who were treated for MRSA skin or soft tissue abscesses, 12% had a history of previous cutaneous abscesses.3 Other studies, which principally involved men with HIV infection, documented recurrences of MRSA skin infections in 31% to 45% of subjects.4-7
In the absence of an effective S aureus vaccine, many clinicians recommend various topical, intranasal, or systemic antimicrobial agents for patients with recurrent MRSA skin infections in an effort to “decolonize” them of MRSA. However, there is scant evidence that decolonization strategies actually prevent recurrent MRSA skin infections. In this article, I discuss some of the most popular decolonization strategies and review the evidence regarding their safety and effectiveness.
PREVALENCE OF S AUREUS NASAL COLONIZATION
The 2001-2002 National Health and Nutrition Examination Survey found that 32.3% of noninstitutionalized persons in the United States harbored S aureus in their nares and that 0.8% of this population were nasal carriers of MRSA.8 By 2004, the overall S aureus carriage rate had decreased to 28.7%, but MRSA carriage had increased to 1.5% (P < .01 for both comparisons).9 Thus, an estimated 4.1 million Americans had MRSA nasal colonization in 2004.9
Colonization rates vary substantially from one geographic region to another, and some locales have reported much higher MRSA carriage rates. In Nashville, Tenn, rates of nasal MRSA colonization among healthy children increased from 0.8% in 2001 to 9.2% in 2004.10 And in 2005, 22% of children hospitalized in Corpus Christi, Tex, had MRSA nasal colonization at the time of admission.11
WIDELY USED DECOLONIZATION STRATEGIES
In 2005, the Emerging Infections Network (EIN) surveyed infectious disease physicians about their practices for preventing recurrent MRSA skin infections. Of 413 respondents, 85% reported prescribing decolonization regimens to about 4400 patients (and 56% had attempted to decolonize other members of the families of about 1800 patients) in the preceding year.12
The survey revealed that decolonization regimens varied widely among infectious disease physicians. These regimens included topical antiseptics, intranasal antimicrobials, and systemic antibiotics, used either alone or in combination for varying durations. The most frequently reported intervention, recommended by 93% of respondents, was intranasal mupirocin(Drug information on mupirocin). Seventy percent of respondents recommended bathing or showering with chlorhexidine(Drug information on chlorhexidine) gluconate, while 14% favored hexachlorophene. Fifty-five percent recommended oral antibiotic therapy, most frequently with rifampin, trimethoprim(Drug information on trimethoprim)/sulfamethoxazole (TMP/SMX), clindamycin(Drug information on clindamycin), or minocycline(Drug information on minocycline).12
A similar range of decolonization regimens was reported by 114 pediatric infectious disease physicians in another EIN survey, conducted in 2006. Only 11% of respondents reported that they did not routinely attempt to decolonize patients with recurrent MRSA skin infections.13
HAND WASHING AND GENERAL HYGIENE
No study has specifically evaluated the effects of hand washing on rates of recurrence of MRSA skin infections. Nevertheless, clinicians are well advised to recommend good hand hygiene to all patients. Hand washing is probably the single most effective intervention for infection control in the home, as it is in the hospital. For example, a randomized controlled trial (RCT) in Pakistan found that pneumonia, diarrhea, and impetigo were significantly less frequent among children in households that received plain soap and hand-washing promotion than in control households.14
Alcohol-based waterless hand sanitizers, which contain 60% to 95% ethanol, are generally more effective for hand antisepsis by health care workers and cause less skin irritation and dryness than does hand washing with soap and water.15 Data on the use of these agents in household settings are limited to 2 studies of families with children in child care. An observational prospective cohort study found that their use was associated with reduced transmission of respiratory infections,16 and an RCT found that their use reduced transmission of GI infections.17 Ethanol is highly active against MRSA in vitro, as will be discussed. The efficacy of alcohol(Drug information on alcohol)-based hand sanitizers for preventing staphylococcal skin infections has not been studied, however.
TOPICAL ANTISEPTICS
Clinicians frequently recommend bathing or hand washing with topical antiseptics for patients with recurrent skin infections. Intuitively appealing as this approach may be, limited data exist to support the efficacy of topical antiseptics or antimicrobial soap in preventing MRSA skin infections.
The 1994 FDA Tentative Final Monograph for Healthcare Antiseptic Drug Products recognizes only 2 biocides as safe and effective for use as antiseptic hand washing agents: povidone-iodine (5% to 10%) and ethanol (60% to 95%).15 These 2 agents, at clinically achievable concentrations, demonstrate better bactericidal activity against MRSA than do other commonly used antiseptics.19
Two studies compared the effectiveness of various antiseptics at reducing MRSA colony counts on experimentally contaminated fingertips. Povidone-iodine (7.5% to 10%) and ethanol (70% to 80%) consistently eliminated more than 99% of bacteria; chlorhexidine (4%) and plain liquid soap achieved bacterial reductions of 96% to 99%; and simply rinsing with tap water eliminated 95.2% of bacteria.20,21
Povidone-iodine. This agent has good antimicrobial activity against MRSA, but its use is frequently associated with skin irritation.15 In addition, concerns about systemic toxicity persist.
In 1980, Block22 reported using topical povidone-iodine in a family of 7 persons, each of whom had severe recurrent furunculosis. Family members applied povidone-iodine to their entire body surface and anterior nares 3 times daily and used it for hand washing. This regimen was associated with a “very marked decrease in frequency of recurrence of staphylococcal furuncles in all family members.” However, it had to be abandoned after 4 children were found to have elevated serum concentrations of thyroid-stimulating hormone. This report served as a warning that systemic absorption of iodine(Drug information on iodine) can occur with topical use of povidone-iodine, not only in neonates and burn victims but also in older children with intact skin.
Chlorhexidine gluconate. This agent has been available in the United States since the 1970s. Although chlorhexidine has generally good antimicrobial activity against gram-positive bacteria, it is significantly less active in vitro against MRSA than it is against methicillin-susceptible strains of S aureus.23,24
In an RCT of 114 MRSA-colonized adults, MRSA was eradicated 30 days after treatment in only 8% of subjects who washed once daily for 5 days with chlorhexidine and in 13% of those who washed with placebo (all patients in this study also applied intranasal mupirocin ointment 3 times daily for 5 days). Chlorhexidine users, however, were more likely than controls to report skin fissures (17.7% vs 1.8%; P = .01), itching (41.5% vs 10.9%; P = .001), and burning of the skin (50.0% vs 9.1%; P < .001).25
Chlorhexidine is no more active than plain liquid soap against MRSA in vitro and on experimentally infected hands. Moreover, its efficacy for skin decolonization remains unproved and its use is frequently associated with dermatitis. Available evidence does not support the use of this agent as part of a MRSA decolonization strategy.
Hexachlorophene. This agent was used frequently in hospitals during the 1950s and 1960s, before it was found to be associated with neurological toxicity in infants. The FDA has not recognized hexachlorophene as safe and effective for use as an antiseptic, and it is dispensed only by prescription.15 Two college football teams employed hexachlorophene showers as part of their strategies to contain MRSA skin infection outbreaks, but the role of this antiseptic in the resolution of the outbreaks is unclear.26,27 In vitro, the bactericidal activity of hexachlorophene against MRSA is comparable to that of chlorhexidine and significantly less than that of povidone-iodine.28
Antimicrobial soaps have become ubiquitous in recent years; one study found that 76% of liquid soaps and 29% of bar soaps available commercially contain either triclosan(Drug information on triclosan) (0.1% to 0.45%) or the related compound, triclocarban.29 Nevertheless, multiple studies have found that antimicrobial soap is no more effective than plain soap at preventing infections of the skin, respiratory tract, or GI tract in household settings.30 Thus, it appears that while the decision to wash one’s hands is critically important, the choice of soap product is less so.
Data regarding the activity of triclosan and triclocarban against MRSA are sparse. In one experimental study, 1% triclosan eliminated MRSA from hands, whereas 4% chlorhexidine did not.31 Two reports have described elimination of MRSA from inpatient neonatal units after the introduction of triclosan-containing soaps (1.0% and 0.3%, respectively), in addition to other infection control measures.32,33
In an RCT involving patients with atopic dermatitis, those who bathed with soap containing 1.5% triclocarban had greater reductions in S aureus colonization and in the severity and extent of skin lesions than did those who used plain soap.34 This study, however, did not specifically focus on patients colonized with MRSA.
Household bleach. The active ingredient of this environmental disinfectant is sodium hypochlorite. The hypochlorite hand rinse has historical significance: Semmelweis demonstrated its effectiveness in preventing mortality from puerperal fever in 1847.35 Hypochlorite is no longer used for hand hygiene, owing to its odor and tendency to cause skin irritation.15
Some clinicians advocate “bleach baths” for patients with recurrent staphylococcal skin infections, despite the absence of published data on the safety or efficacy of this practice. In a review article, Kaplan18 noted that bathing for 15 minutes twice weekly in water to which household bleach has been added (1 teaspoon per gallon of water) might decrease the frequency of furunculosis recurrences. Clinicians and patients should note, however, that one product’s Web site specifically states that bleach “is not for personal usage.”36
