MRSA Infection
(Methicillin-Resistant Staphylococcus aureus) Infection

MRSA Slideshow

• MRSA Infection Overview
• How Common Is MRSA?
• MRSA Infection Causes
• MRSA Infection Risk Factors
• MRSA Infection Symptoms
• When to Seek Medical Care
• MRSA Infection Diagnosis
• MRSA Infection Treatment
• MRSA Infection Prevention
• MRSA Infection Prognosis
• Web Links
• Synonyms and Keywords
• Author and Editor
• Pictures of MRSA - Slideshow

MRSA Infection Overview

MRSA is the abbreviation for methicillin-resistant Staphylococcus aureus. Staphylococcus is a group of bacteria, familiarly known as Staph (pronounced "staff"), that can cause a multitude of diseases as a result of infection of various tissues of the body. In 1959, methicillin, an antibiotic closely related to penicillin, was introduced to treat Staphylococcus and other bacterial infections. Within one to two years, Staphylococcus aureus bacteria (S. aureus) started to be isolated that were resistant to methicillin. These S. aureus bacteria were then termed methicillin-resistant. MRSA usually show resistance to many antibiotics.

Because MRSA is so antibiotic resistant, it is termed a "superbug" by some investigators. This superbug is a variation of an already recognized human pathogen, S. aureus, gram-positive bacteria that occur in grape-like clusters. Distribution of S. aureus is worldwide: As many as 11%-40% of the population is estimated to be colonized. The bacteria are usually found in the human armpit, groin, nose, and throat. In the majority of cases, the bacteria do not cause disease. However, damage to the skin or other injury may allow the bacteria to overcome the natural protective mechanisms of the body leading to infection.

Even without antibiotic resistance, S. aureus has effective means to cause infections. Bacterial strains of S. aureus can produce proteolytic enzymes (enzymes that break down proteins resulting in pus production), enterotoxins (proteins that cause vomiting, diarrhea and in some cases, shock), exfoliative toxin (a protein causing skin disruption, blisters), and exotoxin TSST-1 (a protein that can cause toxic shock syndrome). Adding antibiotic resistance to this long list of pathogenic mechanisms (ways to cause infection) makes MRSA a formidable superbug.

How Common Is MRSA?

About 0.8% (2.3 millions people) of the U.S. population is colonized with MRSA, and these people are called MRSA carriers. The proportion of health-care-associated Staphylococcal infections that are due to MRSA (known as hospitalized or HA-MRSA) rapidly increased from 2% in intensive-care units in 1974 to 64% in 2004. Approximately 126,000 hospitalizations are due to MRSA yearly. Recent data suggest that MRSA causes about 59% of all skin and soft tissue infections. Invasive (serious) MRSA infections occur in approximately 94,000 people each year and are associated with approximately 19,000 deaths, reportedly more deaths than HIV per year. Of these MRSA infections that cause death, about 86% are HA-MRSA and 14% are CA-MRSA (community-acquired MRSA ; MRSA infections that are acquired outside health-care settings).

MRSA Infection Causes

A genetic element that can be transferred from one bacterium to another causes S. aureus to develop resistance to antibiotics. At least five types of genetic material (SCCmec genes I-V) have been identified. Hospital-acquired MRSA (HA-MRSA) usually have genes I-III while community-acquired MRSA (CA-MRSA) have genes IV-V. HA-MRSA is resistant to more antibiotics than CA-MRSA.

MRSA can be transmitted by direct (though skin and body fluids) and indirect contact (from towels, diapers, and toys) to uninfected people. Also, some individuals have MRSA on their body (on their skin or in their nose or throat) but show no symptoms of infection; these people are termed MRSA carriers (see above) and can transmit MRSA to others. Statistics show that CA-MRSA is the predominant MRSA type found in the population.

MRSA Infection Risk Factors

Risk factors for getting MRSA include playing contact sports, sharing towels or other personal items, having any condition that suppresses immune system function (for example, HIV, cancer, or chemotherapy), unsanitary or crowded living conditions (dormitories or military barracks), being a health-care worker, and young or old age. Almost anything that leads to breaks in the skin (for example, scratches, abrasions, or punctures) will increase infection risk. Hospitalized patients are at risk of having health-care workers and MRSA carriers accidently transfer MRSA between patients. Unfortunately, hospitalized patients usually have sites (for example, IV lines, surgical incision sites) that are easily contaminated with MRSA.

MRSA Infection Symptoms

Symptoms of MRSA infections are variable; however, pus production is often found in the infected area. Classic examples of pus-containing areas in patients are boils (pus in hair follicles), abscesses (pus collected underneath the skin), carbuncles (large abscesses with pus draining), sty (pus in the eyelid gland), and impetigo (pus in blisters on the skin). Cellulitis (infection under the skin or fatty tissue) usually does not have pus but begins with small red bumps on skin and also may be due to MRSA. These symptoms are most often found in CA-MRSA but can also be found in HA-MRSA. When antibiotic therapy fails, CA- and HA-MRSA should be considered as a potential cause of infection.

HA-MRSA infections are usually suspected when the hospitalized patient develops signs of sepsis (fever, chills, low blood pressure, weakness, and mental deterioration), even if the patient is being treated with an antibiotic. CA-MRSA patients that develop sepsis or pneumonia (lung infection) need immediate hospitalization. However, hospitalized patients do not need to have a primary site of MRSA infection, only a site where MRSA can invade (invasive or serious MRSA) and proliferate (for example, any surgical site, IV site, or site of an implanted device). Consequently, symptoms of pus production or signs of sepsis in any hospitalized patient, especially those with immune compromise (for example, HIV, cancer, or the elderly) could be due to MRSA.