Prevalence of community-acquired methicillin-resistant Staphylococcus aureus in a private dermatology office

Journal of Drugs in Dermatology, August, 2008 by Aaron M. Bruce, James M. Spencer

ABSTRACT: Background: The prevalence of community-acquired methicillin-resistant Staphlocococus aureus (CA-MRSA) skin and soft tissue infection (SSTI) in private practice dermatology office is largely unknown and the prescribing of antibiotic treatment could be influenced by such data.

Objective: Investigators sought to examine the period prevalence of CA-MRSA infections involving skin and soft tissue in a suburban private practice dermatology setting.

Methods: Chart reviews of 170 patients who had bacterial cultures taken from January 2007 to November 2007 were performed, with an analysis of sex, age, immune status, species of growth, type of lesion, and culture site.

Results: The mean age of the study population was 54.0 years (SD 21.8) and 51.1% were male. Of the 170 cultures taken, 135 (79%) grew 1 or more bacteria and MRSA positive cultures were found in 28 (21%) of 135 cultures.

Limitations: Only 1 geographic location was represented.

Conclusion: The rising rates of CA-MRSA skin and soft tissue infections should be evaluated with consideration of the unique populations that the majority of reports represent. There is little doubt that the prevalence of skin in infections caused by CA-MRSA have increased dramatically and will likely continue to do so in the future. However, the authors caution the empiric prescribing of antibiotics presently known to be effective against CA-MRSA and advocate the culturing of all infectious lesions upon presentation and reserve these antibiotics (tetracyclines, trimetheprim-sulfamethoxazole. [TMP-SMX], clindamycin, rifampin) for the treatment of high-risk patients and patients with culture proven CA-MRSA infections.

INTRODUCTION

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) has become an epidemic in many parts of the world. Reports from emergency rooms, inpatient units, and outpatient clinics have shown MRSA rates of 50% to 80%(1-3). An outbreak has even been reported in a hospital nursery among healthy newborns (4). The implications of these reports are significant, as many physicians may be led to unnecessarily prescribe antibiotics known to be effective against CA-MRSA. Because no reports of the prevalence of CA-MRSA infections in a suburban private practice exist, it is difficult to make recommendations for clinicians practicing in that particular setting.

The first organism known as MRSA was reported in the United Kingdom in 1961 amongst hospital patients. Since that time, several lineages of the MRSA organism have evolved. Community-acquired methicillin-resistant Staphylococcus aureus infections were first reported in 1982 in a group of intravenous drug users. (5) In 1993, Udo et al reported the genetic analysis of CA-MRSA causing virulent skin and soft tissue infections (SSTIs)(6). In the last 10 years the literature has been inundated by reports of escalating rates of MRSA infections in a variety of patient settings. The vast majority of this literature comes from urban settings with high population densities. However, greater than 60% of dermatologists in the US are practicing in suburban (52.2%) or rural locations (10.0%).(7) In 1998, Price and McBride reported data on MRSA infections specific to the outpatient dermatology setting in Houston, Tex.(8)They found an increasing prevalence of MRSA infections starting at 1.5% in 1988 and 11.9% in 1996[R]; however, the exact setting and patient demographics of the clinic were not discussed.

A full discussion of the evolution and biology of the MRSA organisms are beyond the scope of this article. However, it is worth noting that in the US the most common MRSA strain, USA300, has, through horizontal transmission, acquired the arginine catabolic mobile element (ACME)(9). This allows for a selective growth advantage over other MRSA strains. It is hypothesized that S aureus acquired this element from Staphylococcus epidermidis. This may be a factor that is responsible for the growing rates of MRSA infection and brisk disease transmision In addition to this increased capacity for colonization, USA300 also contains a small chromosomal cassette (mec type IVa) that encodes for methicillin resistance. Healthcare associated strains contain a much more extensive chromosomal cassette that carries multidrug resistance genes. In an article by Naimi et al, a complete comparison of health care versus community-acquired S aureus can be found (10). The third trait that may influence the hostile behavior of CA-MRSA is the presence of Panton-Valentine leukocidin (PVL) virulence factor, an exotoxin that can cause necrosis and lysis of leukocytes. However, the idea that PVL is the main virulence factor of many strains of S aureus has been challenged(11).

One of the most significant findings that has been described with CA-MRSA SSTI is the population who acquires the infection most frequently. High-risk groups include athletes, military personnel, prison inmates, intravenous drug abusers, the homeless, children in daycare, and certain Native American groups(12). Folliculitis and abscess formation are reported to be the most common presentations (85%).(12) Despite the high-risk groups, the vast majority of the patients that present with CA-MRSA SSTI are generally in good health. If treated properly, these skin infections rarely progress into systemic illness. There have been reports of the CA-MRSA pulmonary syndrome in children, which in some cases, can be fatal. Although, this syndrome does not originate from clinical skin infections, it does underscore the importance of reducing CA-MRSA colonization. Unfortunately, the best way to accomplish this has not been established.