What is methicillin-resistant Staphylococcus aureus(MRSA)?

MRSA stands for methicillin-resistant Staphylococcus aureus (S. aureus) bacteria. This organism is known for causing skin infections in addition to many other types of infections. There are other designations in the scientific literature for these bacteria according to where the bacteria are acquired by patients, such as community-acquired MRSA (CA-MRSA or CMRSA), hospital-acquired or health-care-acquired MRSA (HA-MRSA or HMRSA), or epidemic MRSA (EMRSA). Statistical data suggest that as many as 19,000 people per year die from MRSA in the U.S.; current data suggest this number has declined by about 25%-35% in recent years, in part, because of prevention practices at hospitals and home care.

Although S. aureus has been causing infections (Staph infections) probably as long as the human race has existed, MRSA has a relatively short history. MRSA was first noted in 1961, about two years after the antibiotic methicillin was initially used to treat S. aureus and other infectious bacteria. The resistance to methicillin was due to a penicillin-binding protein coded for by a mobile genetic element termed the methicillin-resistant gene (mecA). In recent years, the gene has continued to evolve so that many MRSA strains are currently resistant to several different antibiotics such as penicillin, oxacillin, and amoxicillin(Amoxil, Dispermox, Trimox). HA-MRSA are often also resistant to tetracycline(Sumycin), erythromycin (E-Mycin, Eryc, Ery-Tab, PCE, Pediazole, Ilosone), andclindamycin (Cleocin). In 2009, research showed that many antibiotic-resistant genes and toxins are bundled and transferred together to other bacteria, which speed the development of toxic and resistant strains of MRSA. S. aureus is sometimes termed a “superbug" because of their ability to be resistant to several antibiotics.


In addition, these organisms have been termed “flesh-eating bacteria” because of their occasional rapid spread and destruction of human skin. Additionally, a number of older (2004-2008) web and popular press articles are titled or include the erroneous term “MRSA virus.” This is a misnomer that has confused many people; there is no contagious MRSA virus, and if readers examine these articles, they may realize the content is usually about MRSA bacteria.

Unfortunately, MRSA strains of bacteria can be found worldwide. In general, healthy people with no cuts, abrasions, or breaks on their skin are at low risk for getting infected. However, the bacteria can be passed from person to person by direct contact with infected skin, mucus, or droplets spread by coughs. Indirect contact also can spread the bacteria; for example, touching items like towels, utensils, clothing, or other objects that have been in contact with an infected person can spread the bacteria to other uninfected individuals. Investigators estimate that about one out of every 100 people in the U.S. are colonized with MRSA (have the organisms in or on their body but not causing infection) and these individuals may transmit MRSA bacteria to others by the same methods listed above.

What does a MRSA infection look like?

On the skin, MRSA infection may begin as a reddish rash with lesion(s) that looks like a pimple or small boil. Often it progresses to an open, inflamed area of skin (as pictured below) that may weep pus or drain other similar fluid. See the first web citation for more clinical MRSA pictures or see the MRSA slideshow site listed above.

What are the signs and symptoms of MRSA infection?

Most MRSA infections are skin infections that produce the following signs and symptoms:

·         cellulitis (infection of the skin or the fat and tissues that lie immediately beneath the skin, usually starting as small red bumps in the skin);


·         boils (pus-filled infections of hair follicles);


·         abscesses (collections of pus in or under the skin);


·         sty (an infection of an oil gland of the eyelid);


·         carbuncles (infections larger than an abscess, usually with several openings to the skin);


·         impetigo (a skin infection with pus-filled blisters);


·         and rash (skin appears to be reddish or have red-colored areas).

One major problem with MRSA is that occasionally the skin infection can spread to almost any other organ in the body. When this happens, more severe symptoms develop. MRSA that spreads to internal organs can become life threatening. Feverchills,low blood pressurejoint pains, severe headachesshortness of breath, and “rash over most of the body” are symptoms that need immediate medical attention, especially when associated with skin infections. Some CA-MRSA and HA-MRSA infections become severe, and complications such as endocarditisnecrotizing fasciitisosteomyelitis,sepsis, and death may occur.

How is MRSA infection transmitted or spread?

There are two major ways people become infected with MRSA. The first is physical contact with someone who is either infected or is a carrier (people who are not infected but are colonized with the bacteria on their body) of MRSA. The second way is for people to physically contact MRSA on any objects such as door handles, floors, sinks, or towels that have been touched by a MRSA-infected person or carrier. Normal skin tissue in people usually does not allow MRSA infection to develop; however, if there are cuts, abrasions, or other skin flaws such aspsoriasis (a chronic inflammatory skin disease with dry patches, redness, and scaly skin), MRSA may proliferate. Many otherwise healthy individuals, especially children and young adults, do not notice small skin imperfections or scrapes and may be lax in taking precautions about skin contacts. This is the likely reason MRSA outbreaks occur in diverse types of people such as school team players (like football players or wrestlers), dormitory residents, and armed-services personnel in constant close contact.

People with higher risk of MRSA infection are those with obvious skin breaks (for example, patients with surgical or traumatic wounds or hospital patients with intravenous lines,burns, or skin ulcers) and people with depressed immune systems (infants, the elderly, or HIV-infected individuals) or those with chronic diseases (diabetes or cancer). People with pneumonia (lung infection) due to MRSA can transmit MRSA by airborne droplets. Health-care workers as a group are repeatedly exposed to MRSA-positive patients and can have a high rate of infection if precautions are not taken. Consequently, health-care workers and patient visitors should use disposable masks, gowns, and gloves when they enter the MRSA-infected patient’s room.

How is MRSA diagnosed?

A skin sample, sample of pus from a wound, or blood, urine, or biopsy material (tissue sample) is sent to a microbiology lab and cultured for S. aureus. If S. aureus is isolated (grown on a Petri plate), the bacteria are then exposed to different antibiotics including methicillin. S. aureus that grows well when methicillin is in the culture are termed MRSA, and the patient is diagnosed as MRSA infected. The same procedure is done to determine if someone is an MRSA carrier (screening for a carrier), but sample skin or mucous membrane sites are only swabbed, not biopsied. These tests help distinguish MRSA infections from other skin changes that often appear initially similar to MRSA, such as spider bites and skin changes that occur with Lyme disease.

In 2008, the U.S. Food and Drug Administration (FDA) approved a rapid blood test (StaphSR Assay) that can detect the presence of MRSA genetic material in a blood sample in as little as two hours. The test is also able to determine whether the genetic material is from MRSA or from less dangerous forms of Staph bacteria. The test (PCR based) is not recommended for use in monitoring treatment of MRSA infections and should not be used as the only basis for the diagnosis of a MRSA infection.

How can people prevent MRSA infection?

Not making direct contact with skin, clothing, and any items that come in contact with either MRSA patients or MRSA carriers is the best way to avoid MRSA infection. In many instances, this situation is simply not practical because such infected individuals or carriers are not immediately identifiable. What people can do is to treat and cover (for example, antiseptic cream and a Band-Aid) any skin breaks and use excellent hygiene practices (for example, hand washing with soap after personal contact or toilet use, washing clothes that potentially came in contact with MRSA patients or carriers, and using disposable items when treating MRSA patients). Also available at most stores are antiseptic solutions and wipes to both clean hands and surfaces that may contact MRSA. These measures help control the spread of MRSA.

Pregnant women need to consult with their doctors if they are infected or are carriers of MRSA. Although MRSA is not transmitted to infants by breastfeeding, there are a few reports that infants can be infected by their mothers who have MRSA, but this seems to be an infrequent situation. Some pregnant MRSA carriers have been successfully treated with the antibiotic mupirocin cream (Bactroban).

In 2007, the first incidence of MRSA in a pet was recorded. Although relatively rare, MRSA can be transferred between pets and humans. MRSA has been documented in dogs, cats, and horses but may be found in other animals in the future. Care and treatments are similar to those in humans, but a veterinarian should be consulted on all potential cases.

MRSA has been isolated from the environment (for example, beach sand and water), but there is no good documentation that people have become infected from these sources. Most authors suggest prevention methods should consist of a good soap and water shower after visiting the beach.

The CDC does not recommend (2010 guidelines) general screening of patients for MRSA. However, the CDC does recommend that high-risk patients who are being admitted to the hospital be screened for MRSA and then, if positive for MRSA, follow infection control guidelines during the hospital stay. A recent study showed that the number of infections with both HMRSA and CMRSA has dropped since 2005-2008, and authorities speculate that such drops are due to infection control measures in hospitals and better home care measures (listed below).

How should caregivers treat MRSA patients at home?

The CDC states (2010 guidelines) that healthy caregivers are unlikely to become infected while caring for MRSA patients at home if they do the following:

·         Caregivers should wash their hands with soap and water after physical contact with the infected or colonized person and before leaving the home.


·         Towels used for drying hands after contact should be used only once.


·         Disposable gloves should be worn if contact with body fluids is expected and hands should be washed after removing the gloves.


·         Linens should be changed and washed on a routine basis, especially if they are soiled.


·         The patient’s environment should be cleaned routinely and when soiled with body fluids.


·         Notify doctors and other health-care personnel who provide care for the patient that the patient is colonized/infected with a multidrug-resistant organism.

What is the prognosis (outlook), and what are the potential complications for people with MRSA infections?

Statistics from the Kaiser foundation in 2007 ( indicated that about 1.2 million hospitalized patients have MRSA, and the mortality (death) rate was estimated to be between 4%-10%. These data have not been updated by the CDC yet. Another study suggested that the mortality rate may be as high as 23%. In general, the average adult death rate is about 5% of infected patients in 2010. Fortunately, in children under 18 years of age, a recent (2009) study suggests their mortality rate is much lower (about 1%), even though the number of hospitalized children with MRSA has almost tripled since 2002. In general, CA-MRSA has far less risk of any complications than HA-MRSA as long as the patient does well with treatment and does not require hospitalization. However, people who do suffer complications generally have a chance for a worse outcome, as organ systems may be irreversibly damaged. Complications from MRSA can occur in almost all organ systems; the following is a listing of some that can result in permanent organ damage or death: endocarditis, kidney or lung infections,necrotizing fasciitisosteomyelitis, and sepsis. Early diagnosis and treatment usually result in better outcomes and reduction or elimination of further complications.

What is the treatment for MRSA infection?

As stated by the U.S. Centers for Disease Control and Prevention (CDC):

·         "First-line treatment for mild abscesses is incision and drainage."


·         "If antibiotic treatment is clinically indicated, it should be guided by the susceptibility profile of the organism." When the tests are run to determine that the Staph bacteria isolated from a given patient are methicillin resistant, these tests also provide information about which antibiotics can successfully kill the bacteria (its susceptibility profile)."

Fortunately, most MRSA still can be treated by certain specific antibiotics (for example,vancomycin [Vancocin], linezolid [Zyvox], and others, often in combination with vancomycin). Most moderate to severe infections need to be treated by intravenous antibiotics, usually given in the hospital setting. Some CA-MRSA strains are susceptible to trimethoprim-sulfamethoxazole (Bactrim) doxycycline(Vibramycin), and clindamycin (Cleocin); although reports suggest clindamycin resistance is increasing rapidly. In addition, some strains are now resistant to vancomycin.

A good medical practice is to determine, by microbiological techniques done in a lab, which antibiotic(s) can kill the MRSA and use it alone or, more often, in combination with additional antibiotics to treat the infected patient. Since resistance can change quickly, antibiotic treatments may need to change also. Many people think they are “cured” after a few antibiotic doses and stop taking the medicine. This is a bad decision because the MRSA may still be viable in or on the person and thus is capable of reinfecting the person. Also, the surviving MRSA may be exposed to low antibiotic doses when the medicine is stopped too soon; this low dose may allow MRSA enough time to become resistant to the medicine. Consequently, MRSA patients (in fact, all patients) treated with appropriate antibiotics should take the entire course of the antibiotic as directed by their doctor. A note of caution is that, in the last few years, there have been reports of a new strain of MRSA that is resistant to vancomycin (VRSA or vancomycin-resistant S. aureus) and other antibiotics. Currently, VRSA is detected more often than a few years ago, but if it becomes widespread, it may be the next “superbug.”

What is a “superbug”?

The term “superbug” is a nonspecific word that is used to describe any microorganism that is resistant to at least one or more commonly used antibiotics. Some authors restrict its use to microorganisms resistant to two or more antibiotics. Unfortunately, superbug is used in the medical and popular press to describe several different types of organisms which can lead readers to be confused about specific diseases and the infectious agents that cause them. The most common bacteria described as superbugs are the following:

·         MRSA (Staphylococcus aureus strains resistant to multiple antibiotics);


·         VRE (Enterococcus species resistant to vancomycin);


·         PRSP (Streptococcus pneumoniaestrains resistant to penicillin);


·         and ESBLs (Escherichia coli and other Gram-negative bacteria resistant to antibiotics such as cephalosporins and monobactams).

Emerging superbugs may be multiple drug-resistant Clostridium difficile, VRSA (vancomycin-resistant S. aureus) and NDMEscherichia coli (New Delhi metallo-beta-lactamase resistant E. coli).

MRSA Infections At A Glance

·         MRSA means methicillin-resistant Staphylococcus aureus bacteria.

·         The majority of MRSA infections are classified as CA-MRSA (community acquired) or HA-MRSA (hospital- or health-care-acquired).

·         MRSA infections are transmitted from person to person by direct contact with the skin, clothing, or area (for example, sink, bench, bed, and utensil) that had recent physical contact with a MRSA-infected person.

·         The majority of CA-MRSA starts as skin infections; HA-MRSA can begin an infection of the skin, a wound (often a surgical site), or a location where medical devices are placed (catheters, IV lines, or other devices).

·         Cellulitis, abscess, or draining pus is often one of the first signs and symptoms of MRSA infections.

·         Most MRSA infections are diagnosed by culture and antibiotic sensitivity testing ofStaphylococcus aureus bacteria isolated from an infected site; a PCR test is also available.

·         Currently, MRSA bacteria are almost always found to be resistant to multiple antibiotics. All isolated MRSA strains need to have antibiotic susceptibility determined to choose the correct or appropriate antibiotic therapy.

·         Treatment of HA-MRSA frequently involves the use of vancomycin, often in combination with other antibiotics given by IV; CA-MRSA can often be treated on an outpatient basis with specific oral or topical antibiotics, but some serious CA-MRSA infections (for example, pneumonia) often require appropriate antibiotics by IV.

·         Prevention of MRSA is possible by excellent hygiene practices, avoiding skin contact with infected people or items they have touched and by wearing disposable gloves, gowns, and masks when treating or visiting hospitalized MRSA patients. Covering skin abrasions and minor lacerations immediately may also help prevent MRSA infections, especially in children and in people involved in group sports activities.

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