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THE MRSA SCOURGE

MRSAFor the past 25 years, complicated skin and skin structure infections (cSSSIs), more recently termed acute bacterial skin and skin structure infections (ABSSSIs), have placed an increasing burden on healthcare systems.1 This burden is primarily due to the increased spread and persistence of methicillin-resistant Staphylococcus aureus (MRSA) in some regions. Over the last 2 decades, community-acquired MRSA has emerged as the most common cause of purulent skin infections in the US and carries higher rates of complications (such as abscess), recurrence, and treatment failures, often resulting in a need for hospitalization.2 The increased overall burden of managing such common infections has resulted in added healthcare costs.2 Eradication of the causative pathogens requires effective antibiotic therapy against the most likely microorganism. Although recent clinical practice guidelines recommend a range of antibiotic therapies (with or without surgical interventions) for each type of skin infection, management may be challenging for physicians, and patients may suffer from a prolonged hospitalization when suboptimal treatment strategies are initially chosen, when pathogens are drug-resistant, or when comorbidities complicate the infection.3

ABSSSIs and MRSA

The microbiology of ABSSSIs includes not only MRSA but also methicillin-sensitive S. aureus (MSSA) and Streptococcus pyogenes, as well as certain Gram-negative and anaerobic bacteria. Before 2000, MRSA was a rare pathogen in community-acquired (CA) infections and was usually seen in healthcare-associated (HA) infections.4 Since then, the prevalence of CA-MRSA has increased greatly, and CA-MRSA is now a predominant cause of purulent ABSSSI in the US.5

Unlike HA-associated strains, CA-MRSA tends to be more virulent and may carry genes that encode the Panton-Valentine leukocidin, a leukotoxin associated with tissue necrosis and more severe disease.6 Clinical and epidemiologic risk factors do not reliably distinguish CA-MRSA from other pathogens, and, given that CA-MRSA skin infections range from simple cutaneous abscesses to necrotizing fasciitis, it is imperative that treating clinicians recognize the need to provide adequate antimicrobial coverage against MRSA in the empiric setting, such as the emergency department, urgent care clinics, and even office practice.

The ascension of CA-MRSA correlates with a substantial increase in ED visits and hospitalizations in both adult and pediatric patients presenting with ABSSSI. A study of the Kaiser Permanente database showed that the incidence of S. aureus ABSSSIs doubled between 2001 and 2009, while the volume of hospitalizations due to S. aureus ABSSSIs during that interval increased 123%.7 Contributing also to this surge is publicity around clusters of athletes who have shared and spread MRSA infections.8 The fact is, though, that anyone can get MRSA. The risk increases with activities or places that involve crowding, skin-to-skin contact, and shared equipment or supplies. Broken skin, such as when there are abrasions or incisions, is often the site of initiation of an MRSA infection. Athletes, daycare and school students, military personnel in barracks, and residents of nursing homes are at higher risk of MRSA infection.

MRSA is usually spread in the community by physical contact with infected people or things that are carrying the bacteria (“fomites”). This includes contact with a contaminated wound or by sharing personal items, such as towels or razors, that have touched infected skin. The opioid epidemic may also be connected to the rise of Staph infections in communities, because people who inject drugs are 16 times more likely to develop a serious Staph infection.9

Patients with MRSA skin infections often present complaining of a “spider bite.” Unless the spider was actually seen, some other skin break (such as an otherwise almost unnoticeable scrape or cut), it is more likely a Staph infection.10 According to the CDC, Most S. aureus skin infections, including MRSA, appear as a bump or infected area on the skin that might be:

  • red
  • swollen
  • painful
  • warm to the touch
  • full of pus or other drainage
  • accompanied by a fever.9

Staph bacteria, especially MRSA, cause infections that can lead to complications ranging in severity from mild to life threatening, including sepsis, bloodstream infections, pneumonia, and surgical wound infections. Occasionally CA-MRSA infections can be life-threatening. This is much more likely in patients who have a significant comorbidity burden, but even for younger and immunocompetent patients it is worth noting that about 5% of hospitalized patients in the US have MRSA colonizing (that is, present but not infecting) their skin and/or nostrils; fully one-third of the population at large is also colonized.9

Staph bacteria in the not-to-distant past were uniformly sensitive to certain antibiotics, with cephalosporins and methicillin (a modified penicillin) being standard therapy. MRSA is any strain of S. aureus that has developed resistance to these and other drugs, and is a notable part of an evolution towards bacterial resistance, driven mainly by natural selection and certainly by physician overuse of antibiotics, that complicate the care of even common infections, such as ABSSSI and urinary tract infections.

A number of new drugs have been developed to treat MRSA over the past few years, including cetaroline, oritavancin, dalbavancin, omadacycline, and delafloxacin. These drugs have varying dosing regimens, ranging from a one-time infusion, to IV therapy in inpatients, to IV and oral forms that allow smooth transition from inpatient to outpatient care, to oral-only medications. Several of these drugs will be discussed in greater detail in future posts. The importance of a broad arsenal of antibiotics capable of eradicating MRSA cannot be over-emphasized.

1. Edelsberg J, Taneja C, Zervos M, et al. Trends in US Hospital Admissions for Skin and Soft Tissue Infections. Emerg Infect Dis. 2009;15(9):1516-1518. doi:10.3201/eid1509.081228
2. Pollack CV, Amin A, Ford WT, et al. Acute bacterial skin and skin structure infections (ABSSSI): practice guidelines for management and care transitions in the emergency department and hospital. J Emerg Med. 2015;48(4):508-519. doi:10.1016/j.jemermed.2014.12.001
3. Bassetti M, Baguneid M, Bouza E, Dryden M, Nathwani D, Wilcox M. European perspective and update on the management of complicated skin and soft tissue infections due to methicillin-resistant Staphylococcus aureus after more than 10 years of experience with linezolid. Clin Microbiol Infect Off Publ Eur Soc Clin Microbiol Infect Dis. 2014;20 Suppl 4:3-18. doi:10.1111/1469-0691.12463
4. Naimi TS, LeDell KH, Boxrud DJ, et al. Epidemiology and clonality of community-acquired methicillin-resistant Staphylococcus aureus in Minnesota, 1996-1998. Clin Infect Dis Off Publ Infect Dis Soc Am. 2001;33(7):990-996. doi:10.1086/322693
5. Moran GJ, Abrahamian FM, LoVecchio F, Talan DA. Acute Bacterial Skin Infections: Developments Since the 2005 Infectious Diseases Society of America (IDSA) Guidelines. J Emerg Med. 2013;44(6):e397-e412. doi:10.1016/j.jemermed.2012.11.050
6. Chua K, Laurent F, Coombs G, Grayson ML, Howden BP. Antimicrobial resistance: Not community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA)! A clinician’s guide to community MRSA – its evolving antimicrobial resistance and implications for therapy. Clin Infect Dis Off Publ Infect Dis Soc Am. 2011;52(1):99-114. doi:10.1093/cid/ciq067
7. Suaya JA, Mera RM, Cassidy A, et al. Incidence and cost of hospitalizations associated with Staphylococcus aureus skin and soft tissue infections in the United States from 2001 through 2009. BMC Infect Dis. 2014;14:296. doi:10.1186/1471-2334-14-296
8. Jiménez-Truque N, Saye EJ, Soper N, et al. Association between Contact Sports and Colonization with Staphylococcus aureus in a Prospective Cohort of Collegiate Athletes. Sports Med Auckl NZ. 2017;47(5):1011-1019. doi:10.1007/s40279-016-0618-6
9. General Information | MRSA | CDC. https://www.cdc.gov/mrsa/community/index.html. Published June 26, 2019. Accessed February 9, 2020.
10. Dominguez TJ. It’s Not a Spider Bite, It’s Community-Acquired Methicillin-Resistant Staphylococcus aureus. J Am Board Fam Pract. 2004;17(3):220-226. doi:10.3122/jabfm.17.3.220

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