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MRSA Infections: 3 Ways to Avoid Colonization and Infection

Addressing MRSA and how to protect yourself from an infection

MRSA: Bacteria and the human state

The state of being human is anything but static. Humans are home to many bacteria, viruses, and fungi. By order of magnitude, there are more non-human cells than human cells on the surfaces and within the body’s orifices (10 to 14th compared to 10 to 13th). Bacteria colonize any surface in contact with the environment, such as the skin, mouth, upper respiratory tract, gastrointestinal system, urinary tract, vagina. Scientists call the environment and bacteria which grow in it the microbiome. Different microbes prefer a particular surface based on multiple factors, including pH, temperature, protein sources, oxygen content, and moisture/salinity.

Staphylococcus aureus colonizes the groin, perineum (area between genitals and anus), axillae (armpits). But the nasopharynx (nose and throat) is its primary habitat. As many as 25% or more of the population harbors S. aureus in the nose. Much less are colonized with MRSA (2-4%). A discussion of the complex relationship between S. aureus and humans in colonization and infection follows.

Compared to oral and intestinal surfaces, bacterial colonization on the surface of the skin is sparse. The 1.2 kg of total body weight accounts for bacteria, with skin bacteria weighing approximately 0.2 kilograms and intestinal bacteria weighing 1 kg. Bacteria reside on the skin’s surface generally as commensals or “neutralists,” a relationship with the human host that is neither beneficial nor detrimental.

Bacteria utilize various elements on the surface, such as carbon, oxygen, nitrogen, potassium, magnesium, iron, and calcium, to grow optimally. However, given the right circumstances, such as trauma, skin abrasion, or excessive dryness (xerosis), there is a transition from more significant colonization to infection. 

The most common bacteria associated with skin infections are Streptococcus and Staphylococcus. Streptococcus causes impetigo, a superficial infection. It causes wound infections from injury or after surgery, and cellulitis, an ascending infection associated with fever, rash and pain, and swelling of the site. Staphylococcus aureus infections include wound infections, folliculitis, furuncles, carbuncles (skin abscesses or “boils”), and deeper, more serious conditions if left unchecked. 

With Staph and Strep, deeper infections can occur. These infectious such as necrotizing fasciitis or a muscle abscess (pyomyositis), may require surgical intervention. An untreated Staphylococcus aureus infection can predispose to abscesses in the epidural space or even heart valve infections (endocarditis). Staphylococcus aureus can sometimes follow viral respiratory infections leading to severe, life-threatening pneumonia.

An abscess requires an incision and drainage.

Staphylococcus aureus is easy to see on Gram staining. They stain Gram-positive (purple) and appear as grape-like clusters in the microscope. They grow readily on culture media, including blood cultures. Newer testing methods, including a nasal swab for PCR, help detect colonization of Staph aureus in the nares and differentiating between MRSA and MSSA. Colonizatoin has clinical utility for treatment and pre-operative preparation.

Gram-positive (Staph aureus) stain purple; Gram-negative stain pink

Staphylococcus aureus (including MRSA) is a Gram-positive staining microbe

MRSA: Question and Answer

What is MRSA?

Methicillin-resistant Staphylococcus aureus is a ubiquitous bacterium that resides on the skin and nasal-oropharynx of humans and other animals. The ecological niche of Staphylococcus aureus in the nares (nose). Others areas of the skin populated by this bacterium include the axillae (armpits), groin, perineal area (area between genitals and anus). Contamination of fomites (inanimate objects such as keys, computers, phones etc) can represent a transmission source to other people. Although colonization generally precedes infection, outbreaks may occur where colonization was not evident.

Methicillin-resistant Staphylococcus aureus (MRSA). This form of Staphylococcus aureus carries resistance to methicillin (including others such as oxacillin; cefazolin), an iteration of penicillin produced in 1959. It provided a short period of coverage against penicillin-resistant Staph, associated with the production of an enzyme beta-lactamase, which could break down the penicillin structure (beta-lactam ring), neutralizing its activity. Unfortunately, not long after its use, Staph bacteria capable of growing in its setting appeared, initially in the hospital setting. 

In the ’80s and ’90s, a growing percentage of community-associated infections from MRSA appeared. Various proteins expressed by MRSA, such as the Panton Valentin Leukocidin (PVL) and others, are associated with outbreaks and, to some extent, a greater virulence (more severity) of infection. Co-association with the colonization of MRSA and MSSA can be attributable to a risk of diseases after surgery. 

I had a Spider bite that got infected with MRSA. Is this possible?

Typically, when someone is in the process of developing an infection with Staphylococcus aureus, the area may feel a sharp pain. Although the sensation is similar to an insect or spider bite, it is seldom the case. Indeed, in various geographic locations, the bite of a brown recluse or hobo spider, to name a few, can result in an erythematous lesion with central necrosis (dark center). 

Often, “spider bites” are really abscesses that culture Staphylococcus aureus in the wound. In one study by Moran et al., a report of a spider bite had an adjusted odds ratio of 3 (that means that those with this history were 3x more likely than those without an MRSA infection.

What are the risk factors for MRSA infection?

This question is one with a complicated answer. 

Miller and Binh an Diep CID 2008 had an excellent way of representing risk factors in three areas:

Risk factors of behaviors and exposures: skin-to-fomite contact (shaving, tattoos, rug burns, etc.), skin-to-skin contact, antibiotic exposure

Host defenses: Skin integrity, Antimicrobial peptides, an area that is in its infancy but essentially looking at proteins that the skin produces which neutralize bacteria, etc., medications that affect the immunity such as biologicals, e.g., TNF-a antagonists (etanercept, etc.), chemotherapy, steroids, etc. Immunodeficiency states. 

 Pathogen factors: These relate to virulence factors, toxins produced. strain type, etc.

What are some epidemiologic associations of MRSA infection?

  1. Locations: Prisons, athlete groups/gyms, astroturf, hospitalization, military, reservations
  2. Behaviors: Men who have sex with men (MSM), Elicit drug use (meth/heroin), shavers
  3. Conditions: HIV, Hepatitis C, Diabetes mellitus and cirrhosis, Job’s syndrome, Paraplegia
  4. Medications:  Recent antibiotic exposure, Steroid use (prednisone) or other immunosuppressants, possible association with nonsteroidal agents (NSAIDS)
  5. Devices: Hemodialysis catheters, Peripherally inserted central catheters (PICC), foleys, PEG tubes, etc

How do I prevent myself from getting MRSA?

Approximately 10-25% of the population harbors Staphylococcus aureus – sensitive or MSSA. Three percent is colonized with MRSA. Suggestions for avoiding colonization are somewhat similar to those suggestions for preventing infection:

 1. Good handwashing, regular (but not excessive) showering, and laundering – increased rates of MRSA in poor hygiene practices. Wash hands after touching or picking the nose.

 2. Use sharp razors for shaving (avoid blunt trauma) but avoid cutting trauma. Apply alcohol to the razor before/after use. Do not share razors. Use a moisturizer for skin after shaving. 

 3. If you have dermatitides such as eczema, psoriasis, or others, make sure it is treated. You have a higher rate of colonization with Staph.

 4. Use antibiotics judiciously – you play an essential role in limited antibiotic use!

 5. If you develop a pimple, DON’T attempt to express it. When the process is deeper, the attempt may fail and lead to more inflammation which means more abscesses. Most people I see that require an incision and drainage have admitted to having attempted too vigorously to express a furuncle.

 6. Use NSAIDs and Steroids judiciously. 

 7. Keep your skin well lubricated with humectants, as drying can promote skin and dermatitis/eczema breaks. Plan on applying skin creams after you have dried yourself from your shower/bath. 

 8. Move your body around. Sitting on your butt, kneeling, or leaning on your elbows too long promotes skin changes that can lead to breaks in the skin in these areas. For this reason, I see many MRSA abscesses in paraplegics/quadriplegics or others that have limited motion.

9. Get plenty of quality sleep and exercise (don’t underestimate the role of these factors on the immune system). 

After decolonization, recolonization recurs in a large number. However, it does not mean that you will get another abscess. With greater awareness of cause and prevention measures, it is with hopes that Staph aureus will not cause recurrent problems.

An approach to the treatment of MRSA in a person presenting with an infection is three-fold.

A person that is colonized with Staph aureus has a higher risk of infection after an orthopedic surgery, like a knee replacement. Physicians and surgeons are routinely checking patients for nasal colonization with the nasal PCR. If it is found, decolonization attempts are pursued.

Patients will commonly come into the clinic to search for answers on how to reduce the risk of future infections. As summarized in the previous sections, underlying conditions, behaviors, and medications predispose to recurrent Staph infections. Optimal control of future infections needs to include strategies to improve these conditions and risk factors. Someone with chronically elevated glucoses will continue to develop Staphylococcus aureus infections, in spite of approaches to eradicate colonization.

There are three ways that I approach patients with persistent MRSA infections and colonization:

1. Address the risk factor

For a state of colonization to transform to a state of infection, there is often a risk factor that can be identified.  Some are more obvious than others.  Occasionally, upon examining a patient, I can tell the risk factor.  For instance, some men (swimmers, other athletes) are shavers; some women shave closer to the groin or mons pubis.  Using a dull razor, not using a cream or moisturizer to shave, or not treating the razor with alcohol prior to use can lead to a break in the skin and allow the bacteria to cause an infection. 

Sometimes, a new sexual partner of a patient was colonized with Staph and increases the risk of transmission, enough to lead to folliculitis and abscesses.  On the examination, I will often observe a patient scratching themselves where they have dry skin or folliculitis and even attempt to express a lesion in front of me. 

People who are chronic sitters, e.g. truck drivers, writers, bloggers (one of many reasons I have a standing desk…) are also prone to folliculitis on the buttock, which can then cause an abscess.  Below. I have listed several ways to reduce the risk of Staph aureus infection.

2. Address the infection

The infection state may be an abscess or other skin lesions. To address the infection, physicians perform an incision and drainage of a boil, if present; or sometimes, allow it to mature and resolve spontaneously.  Some data support that antibiotics have a limited role after an incision and drainage of a small <2cm abscess.  Though with larger abscesses, there has been found a lower failure rate than with a proper incision and drainage.  Antibiotic consideration include trimethroprim-sulfamethoxazole (bactrim), doxycycline and possibly clindamycin (some resistant isolates). 

3. Address the colonization state

Again, the usual colonization site is the nose and skin and  can be addressed after the infection is treated.  For decolonization, I prescribe a surgical cleanser, such as Hibiclens, which can be applied 2 to 3 times weekly – lather on the skin and rinse off.  For the nasal carriage, an antibiotic ointment such as bactroban (nasal bactroban) can be used – apply a cotton swab with the ointment in each naris twice daily for 1 week.  I usually begin this protocol 2 weeks after the acute infection is treated.

Thanks for reading This! Dr. Cirino

Further reading (below are a few references and links):

Boeker S et. al. Methicillin-resistant Staphylococcus aureus: risk factors associated with community-onset infections in Denmark – Clinical Microbiology and Infection. 2008. Clin Micro and Infection. Danish Community-MRSA group.

Moran er al. N Engl J Med 2006; 355:666-674   (Epidemiology)


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