MRSA Skin Infection in Athletes 

Nosocomial infections of methicillin-resistant Staphylococcus aureus (MRSA) (ie, hospital-acquired MRSA [HA-MRSA]) have been reported since 1963.^[1] Community-acquired MRSA (CA-MRSA) infections are a more recent variant and are becoming more common in athletes^{[2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]} and active individuals since the first reported cases in a high school wrestling team in 1993^[13] and a British rugby club in 1998.^[14] CA-MRSA differs from HA-MRSA in its genetic makeup, increased pathogenicity, and susceptibility to antibiotic treatment.^{[15, 16, 17]}

The resistance of MRSA to beta-lactam antibiotics is due to the presence of the mecA gene sequence. The mecA gene produces transpeptidase PBP2a (penicillin-binding peptide) that decreases the bacterial affinity of the beta-lactam antibiotics. The mecA gene is a subset of a larger SCCmec gene that is responsible for the differences seen in HA-MRSA and CA-MRSA bacteria.^{[16, 18]}

Several variations of the SCCmec gene have been sequenced; SCCmec gene types I, II, and III are found in HA-MRSA, whereas CA-MRSA bacteria have the SCCmec type IV gene.^[19] The SCCmec gene types I-III are larger genes, and other portions of the gene provide resistance factors against other antibiotic classes. The type IV SCCmec gene is a small gene that has fewer of these additional resistance factors. This difference may explain the continued susceptibility of CA-MRSA compared with HA-MRSA to some oral antibiotics such as trimethoprim-sulfamethoxazole.

For excellent patient education resources, visit eMedicine's Blood and Lymphatic System Center; Infections Center; Cuts, Scrapes, Bruises, and Blisters Center; and Environmental Exposures and Injuries Center. Also, see eMedicine's patient education articles MRSA Infection, Sepsis (Blood Infection), Life-Threatening Skin Rashes, and Antibiotics.

CA-MRSA has been found in some cases to be a more virulent form compared with HA-MRSA. Up to 70% of CA-MRSA strains contain the Panton-Valentine leukocidin (PVL) virulence factor, including the most common form of CA-MRSA isolated from outbreaks in the United States.^[20]

MRSA colonization

Studies have shown that approximately 25-30% of the population is colonized with methicillin-sensitive S aureus bacteria. Colonization is usually on the skin or in the nasal passages. One study demonstrated a 3% rate of MRSA nasal colonization in adult patients visiting an outpatient clinic for unrelated medical appointments.^[21] A similar study in an outpatient pediatric population detected MRSA colonization rates slightly above 1%.^[22]

CA-MRSA infections in the general population

A prospective study in an Oakland, California, emergency department found that 51% of patients with a skin infection who presented for evaluation and treatment had positive culture results for MRSA; 99% of the MRSA infections contained the type IV SCCmec gene that is associated with the CA-MRSA strain, and 94% of MRSA isolates also contained the PVL gene.^[23]

CA-MRSA outbreaks in athletes and other populations

Most publicized reports of CA-MRSA infection have been in college or professional football teams.^{[2, 3, 4, 5, 6, 7]} However, outbreaks have also been reported in other sports, such as wrestling, rugby, and fencing. In a study of all Nebraska high schools between 2006 and 2008, Buss et al determined that among the schools that responded, MRSA infections rose from 4.4% in school year 2006-2007 to 14.4% in 2007-2008; the incidence per 10,000 wrestlers rose 3-fold from 19.6 to 60.1 and that per 10,000 football players increased 5-fold from 5.0 to 25.1.^[10]

Other populations at risk for CA-MRSA outbreaks include military recruits, children in day care, prison inmates, homosexual men, injection drug users, and veterinarians, particularly those who have contact with farm animals, notably pigs.^{[5, 24, 25]}

Most CA-MRSA infections initially manifest as folliculitis or a similar soft-tissue or skin infection. Typically, the athlete may describe his or her presentation as an "infected pimple" or "insect bite." Some CA-MRSA infections may have progressed to abscess formation. In other cases, the infection may manifest as a life-threatening illness, such as a rapidly progressing sepsis or pneumonia.

The initial clinical examination usually reveals a limited area of redness, warmth, and swelling that is consistent with folliculitis. Occasionally, the patient may have swelling and pain in a joint. In more advanced cases, moderate to severe pain at the site of the infection may be reported; the pain may be due to soft-tissue necrosis from PVL activity.

Transmission

In severe cases of CA-MRSA infection, endocarditis, septicemia, necrotizing fasciitis, osteomyelitis, and multisystem organ failure, or death due to overwhelming sepsis may occur. Severe cases may progress extremely rapidly from the initial manifestation of an abscess.

The most common route of transmission of CA-MRSA is though an open wound, such as a superficial abrasion, or from contact with a CA-MRSA carrier. Other methods of transmission include poor hand washing, poor personal hygiene (eg, not showering after workouts), sharing personal items (eg, razors, towels, clothing), or a failure to properly clean and disinfect exercise and training equipment.

Outpatient treatment

The primary method of treatment for CA-MRSA skin and soft-tissue infections includes incision and drainage (I&D) of the abscess and therapy with appropriate antibiotics when indicated. Wound exudates should be cultured to accurately determine the causative organism and appropriate antibiotics for therapy.

The susceptibility of CA-MRSA is dependent on local resistance rates (US Centers for Disease Control and Prevention guidelines [see Antibiotic/Antimicrobial Resistance: Clinical Guidelines and CDC Surveillance Systems and Published Data, as well as Diseases Connected to Antibiotic Resistance: Methicillin-Resistant Staphylococcus aureus (MRSA)]). Typical treatment choices include oral antibiotics.

• Oral antibiotics

  • Trimethoprim-sulfamethoxazole (Bactrim DS; available as generic) twice daily, with or without rifampin, at 600 mg/d. Note: Rifampin is not a first-line drug for CA-MRSA, but this agent may be used in conjunction with other antibiotics for infections that do not respond to the initial treatment or for patients who experience recurrent infections.
  • Doxycycline at 100 mg twice daily
  • Clindamycin at 450 mg 3 times a day (96% sensitive): Resistance to clindamycin is increasing because of the inducible macrolide-lincosamide-streptogramin B (iMLSb) phenotype, which may result in cross-resistance to clindamycin.
  • Tetracycline
  • Minocycline
  • Not recommended due to resistance
    • Ciprofloxacin: This drug has a 33% sensitivity in some areas. Ciprofloxacin is not a good choice in pediatric patients because of concerns about its effect on growth plates.
    • Cephalexin (Keflex; MiddleBrook Pharmaceuticals, Inc, Germantown, Md)
  • Not recommended due to poor oral absorption
    • Oral vancomycin

Length of treatment

There are no well-controlled studies that demonstrate an optimal length of antibiotic treatment for CA-MRSA.

Inpatient treatment

Treatment of moderate to severe CA-MRSA infections may require surgical debridement of the abscess, intravenous antibiotics, and hospitalization. The need for hospitalization should be made on a case-by-case basis.

• Intravenous antibiotics

  • Vancomycin: Note that reports have described some intermediate vancomycin susceptibility in Japan, Texas, and New York.
  • Some studies also indicate vancomycin treatment failure with MRSA bacteremia is associated with high mortality rates (1) when this agent is initiated after an inappropriate empiric antibiotic was used and (2) when vancomycin itself is the empiric agent in cases when the infective strain had a high vancomycin minimum inhibitory concentration (MIC).^{[26, 27]} Another study demonstrated previous antibiotic exposure is itself a risk for MRSA isolation.^[28]
  • Linezolid at 600 mg twice daily: The FDA warns against the concurrent use of linezolid with serotonergic psychiatric drugs, unless indicated for life-threatening or urgent conditions. Linezolid may increase serotonin CNS levels as a result of MAO-A inhibition, increasing the risk of serotonin syndrome.^[29]
  • Daptomycin at 4 mg/kg/d
  • Quinupristin-dalfopristin at 7.5 mg/kg every 8-12 hours

Investigational antibiotics

There are 2 anti-CA-MRSA beta-lactams, ceftaroline (cephalosporin) and ME1036 (carbapenem), that are under investigation. A preliminary study of susceptibility testing indicated that ceftaroline was 64-fold more potent than ceftriaxone, whereas ME1036 was >128-fold more potent than ceftriaxone.^[30] All isolates had the PVL genes and type IV SCCmec, and 67.8% showed the USA300-0114 strain, cloned via pulsed field gel electrophoresis (PFGE).

Another agent that is under study and that may hold potential for the prevention of catheter-associated infections, particularly against MRSA, is omiganan pentahydrochloride, a novel topical cationic peptide.^[31]

Recurrent infections

If an athlete has recurrent MRSA infections, suspect resistance to the previous antibiotic or nasal colonization, and send a nasal swab for culture. A different antibiotic may also be prescribed if the practitioner is concerned about a poor response to treatment. If the nasal swab culture is positive for CA-MRSA, then treat with mupirocin antibiotic ointment (Bactroban; GlaxoSmithKline, Research Triangle Park, NC) twice a day applied to the nares and oral rifampin at 300 mg twice daily for 7 days.

Several key methods can be used for prevention of the spread of CA-MRSA infections. Because the most common source of infection is from close contact or from an open wound, preventive measures should focus on proper hygiene. Hand washing, using soap and water or antibacterial hand gels, should be encouraged by the infected patient and by individuals who come in direct contact with the patient. Additionally, open wounds and abrasions should be covered and protected.

Athletes should be educated and instructed to not share personal hygiene products such as razors or towels. Medical and training staff should continue to practice universal infectious disease protection measures. These personnel should ensure the proper disposal of bandages after dressing changes and the routine cleaning of equipment such as training tables, whirlpools, and exercise mats.

Athletes with mild cases of CA-MRSA infections may be allowed to return to athletic participation once an appropriate antibiotic treatment has commenced and the risk of transmission to other athletes has been significantly reduced or eliminated. Abrasions should be covered with a protective covering, and the athlete should be reevaluated daily for signs or symptoms of recurrence or worsening of the infection. The athlete and teammates should also be counseled about the need to avoid sharing towels, razors, or other personal items. Training staff should ensure proper disinfection of equipment and surfaces with which the infected athlete may come in contact, such as training tables, protective equipment, or wrestling mats, among other items.