What's MRSA?

Infection with a superbug--


Despite its exotic-sounding name, there's nothing mystical about methicillin-resistant Staphylococcus aureus (MRSA), a type of bacteria that is resistant to several classes of antibiotics.  This bacteria is all around us.  The CDC estimates that 2 individuals in 100 people are colonized with MRSA, and these people harbor it in nasal secretions.  Many of these people who are colonized are without infection; colonization with MRSA doesn't necessarily lead to disease.

  However, in group settings like prisons, locker rooms, and barracks, and among hospitalized patients with weakened immune systems, MRSA can wreak havoc.  In community settings, big pus-filled abscesses are par for the course, and in the hospital, pneumonia and septicemia caused by MRSA kill.

Although overlap exists, MRSA is commonly divided into 2 groups:  hospital acquired and community acquired.

Hospital-Acquired MRSA (HA-MRSA)

In a hospital setting, HA-MRSA is one of several nosocomial pathogens.  What makes HA-MRSA particularly scary is it preys on the weak and it can cause deep infection.  Specifically, infection with HA-MRSA can cause the following deadly complications:

  • cellulitis (skin infection)
  • toxic shock syndrome
  • endocarditis (heart infection)
  • osteomyelitis (bone infection)
  • sepsis (blood poisoning)

Because it is resistant to beta-lactam antibiotics--including penicillins and all except fifth generation cephalosporins--infection with HA-MRSA is hard to treat.

  In an inpatient setting, HA-MRSA is usually treated with the heavy-hitting antibiotic vancomycin.  Other first-line treatments include linezolid for pneumonia and daptomycin for complications other than pneumonia.

Fortunately in recent years, thanks to organized healthcare efforts, the prevalence of HA-MRSA has dramatically decreased by a little more than half between 2005 and 2011.

  Two strategies to rope in MRSA in hospital settings are the "MRSA bundle" and universal decolonization.  The MRSA bundle involves contact precautions, hand washing, nasal surveillance for MRSA and making infection control a personal responsibility of all health care personnel.  Another successful measure to combat HA-MRSA is "universal decolonization" where all ICU patients are bathed with chlorhexidine and decolonized with nasal mupirocin. 

Community-Acquired MRSA (CA-MRSA)

Many people who are infected with CA-MRSA think they've been bitten by a spider.  While spider bites are rare, skin infection with CA-MRSA is common.  

Infection with CA-MRSA typically presents as inflamed and painful (pus-filled) abscesses or boils.  Localized skin infection can also be accompanied by fever.  This bacteria thrives in community settings--where people share close living quarters like prisons, locker rooms, dormitories or barracks.  CA-MRSA is also common among patients on dialysis, IV drug abusers, people with diabetes and people who have just received treatment with corticosteroids (which depress the immune system).

When the abscess is ripe, a primary care physician will perform an incision and drainage and, depending on the size of the infection, prescribe antibiotics.

If a drained abscess is greater than 5 centimeters, physicians typically prescribe with MRSA in mind--oral antibiotics like Keflex (a third-generation cephalosporin) for streptococcal coverage and Bactrim for MRSA.  Of note, most MRSA are insensitive to fluoroquinolones and essentially all cephalosporins.

For a skin infection caused by CA-MRSA, Bactrim is usually prescribed.  Bactrim works by inhibiting folate synthesis by bacteria. 

After one week of therapy, make sure to follow up with your physician.  By that time, the infection should clear.  In the unlikely event that the infection fails to clear, expect a wound culture and possible shot of Rocephin. 

While the prevalence of hospital-acquired MRSA has decreased, cases of CA-MRSA are on the rise.  In fact, CA-MRSA is creeping into hospital settings!  There is some concern that these two bugs may possibly recombine thus making for a more deadly infection.

If you or a loved one have a skin infection like a boil that is exquisitely red, inflamed and tender, it's important to see a primary care physician.  Your physician can drain the abscess of pus.  Depending on the size of the abscess or extent of infection, you may also need antibiotics.  Please keep in mind that an abscess or boil needs to form a "head" or become soft in order to be drained.  If the abscess has yet to form a head, your physician will send you home with instructions to apply warm compresses to the boil and follow up in a few days for incision and drainage.

You can also decrease your risk of acquiring community-acquired MRSA (CA-MRSA)  by washing your hands regularly, cleaning your clothes well and not sharing your personal effects to yourself (think towels, razors, and clothing). 

If you are infected with CA-MRSA, it's imperative that you keep your wound and bandaging clean so as to heal and avoid infecting others.  You must also make sure to take your full course of antibiotics so as to mitigate antibiotic resistance.  Finally, please don't attempt to drain a boil by yourself--doing so can worsen infection and spread it to others.

Selected Sources

Munoz-Price L. Chapter 186. Antibiotic Resistance. In: McKean SC, Ross JJ, Dressler DD, Brotman DJ, Ginsberg JS. eds. Principles and Practice of Hospital Medicine. New York, NY: McGraw-Hill; 2012. Accessed March 23, 2015.

Wachter RM. Chapter 10. Healthcare-Associated Infections. In: Wachter RM. eds. Understanding Patient Safety, 2e. New York, NY: McGraw-Hill; 2012.  Accessed March 23, 2015.

Continue Reading