MRSA

  • Medical Author:

    Sandra Gonzalez Gompf, MD, FACP is a U.S. board-certified Infectious Disease subspecialist. Dr. Gompf received a Bachelor of Science from the University of Miami, and a Medical Degree from the University of South Florida. Dr. Gompf completed residency training in Internal Medicine at the University of South Florida followed by subspecialty fellowship training there in Infectious Diseases under the directorship of Dr. John T. Sinnott, IV.

  • Medical Editor: Melissa Conrad Stöppler, MD
    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

Digitally colorized scanning electron micrograph (SEM) depicts four green-colored, spheroid-shaped, methicillin-resistant Staphylococcus aureus (MRSA) bacteria, as they were in the process of being enveloped by a much larger human white blood cell.

MRSA infections facts

  • Staphylococcus aureus (Staph aureus, S. aureus, or SA) is a common bacteria (a type of germ) in the nose and on the skin of people and animals.
  • MRSA means "methicillin-resistant Staphylococcus aureus." It is a specific "staph" bacteria (a type of germ) that is often resistant to (is not killed by) several types of antibiotic treatments. Most S. aureus is methicillin-susceptible (killed by methicillin and most other common treatments).
  • In general, healthy people with no cuts, abrasions, or breaks on their skin are at low risk for getting infected.
  • About one out of every three people (33%) are estimated to carry staph in their nose, usually without any illness. About two in 100 (2%) carry MRSA. Both adults and children may have MRSA.
  • Like common S. aureus (SA), MRSA may cause deep (invasive) or life-threatening infections in some people. Because it is resistant to commonly used antibiotics, it can be harder to treat or become worse if the right treatment is delayed. MRSA is one of the bacteria listed by the U.S. Centers for Disease Control and Prevention (CDC) as a "superbug" resistant to multiple antibiotics.
  • MRSA skin infections can be picked up either in the general community (community-associated MRSA or CA-MRSA infection) or in health care facilities (health care-acquired or HA-MRSA). In the hospital, MRSA can cause wound infections after surgery, pneumonia (lung infection), or infections of catheters inserted into veins. Invasive MRSA infections include soft tissue infections, heart valve infections, bone infections, abscesses in organs, joint infections, or bloodstream infection (sepsis, "blood poisoning").
  • Because HA-MRSA can be life-threatening, the National Healthcare Safety Network (NHSN) and Emerging Infections Program (EIP) of the CDC monitor hospital MRSA rates. The CDC also advises hospitals and health professionals about preventing and lowering MRSA infection rates.
  • Rates of MRSA bloodstream infections in hospitalized patients fell nearly 50% from 1997-2007 since hospitals began using prevention measures. MRSA is transmitted from person to person by direct contact with the skin, inhaling droplets from coughing, or items touched by someone who has MRSA (for example, sink, bench, bed, and utensils). People can be carriers of MRSA even if they don't have an infection. This is called colonization. A common place for MRSA colonization with MRSA is inside the nose.
  • One way to keep visitors and health-care staff from carrying MRSA from one patient to others is to follow CDC-guided precautions by wearing disposable gloves and gowns (and sometimes masks) when visiting hospitalized people who have MRSA. A sign at the door provides instructions that should be carefully followed.

Quick GuideMRSA Infection: Causes, Symptoms, and Treatment

MRSA Infection: Causes, Symptoms, and Treatment
Read about MRSA infection symptoms and signs.

MRSA Symptoms and Signs

Superbug Staph Spread in Community

Community-associated MRSA infections usually affect the skin, causing pimples and boils in otherwise healthy people. Infected areas may be red, swollen, painful, and have pus or other drainage.

	A petri dish culture plate demonstrates the growth of methicillin-resistant Staphylococcus aureus (MRSA) bacteria.

What is methicillin-resistant Staphylococcus aureus (MRSA)?

Staphylococcus aureus (SA) is a common skin bacteria. It is sometimes called staph, and it most often causes skin and soft tissue infections. Although S. aureus has been causing staph infections as long as humans have existed, MRSA has only been around since 1961. Methicillin was one of the first antibiotics used to treat S. aureus and other infections. S. aureus developed a gene mutation that allowed it to escape being killed by methicillin, so it became resistant to methicillin. That makes it harder to treat someone who gets an infection. Stronger, more expensive, or intravenous antibiotics may be needed.

Since the 1960s, MRSA has picked up more resistance to different antibiotics. Overuse of antibiotics has increased resistance in MRSA and other infectious bacteria, because resistance genes (the genes that code for resistance) can be passed from bacteria to bacteria.

If a doctor orders a test for bacteria on a specimen of pus, for example, the laboratory will alert the doctor if the test shows MRSA, so that precautions can be taken, and the right treatment can be started.

A 1961 technologist works in a lab and examines petri dishes.

What is methicillin-resistant Staphylococcus aureus (MRSA)? (Continued)

A deadly complication of MRSA is a deep infection, necrotizing fasciitis, which causes rapid spread and destruction of human tissues. Some but not all strains of MRSA are more likely to behave like "flesh-eating bacteria." It is impossible to predict which MRSA infection will be "flesh-eating."

How many strains of MRSA are there?

In general, there are two major strains of MRSA, "community-acquired” or CA-MRSA and "hospital acquired" or HA-MRSA. CA-MRSA differs from HA-MRSA in that it is often resistant to fewer antibiotics and it is by definition picked up outside of the hospital or health care institution. CA-MRSA strains are often able to cause more severe and deeper infections in healthy people than HA-MRSA. They often have a variety of "virulence factors" that are responsible for this. Some of these are "leucocidin" proteins that are toxic to immune cells that fight infections or cause more inflammation and tissue damage; Panton-Valentine leucocidin (PVL) protein is a well-known example that is produced by the USA300 strain of CA-MRSA. The "phenol-soluble modulin" (PSM) proteins are a recently discovered class of leukocidins that increase the likelihood of causing severe disease in various ways.

Most HA-MRSA infections have been due to the USA100 strain. HA-MRSA is more likely to affect people in health care institutions who may have weaker immune systems due to other illnesses. HA-MRSA is less likely to cause problems for healthy people in the community.

View MRSA Slideshow
An illustration shows a lesion caused by a methicillin-resistant Staphylococcus aureus (MRSA) bacterial infection.

What does a MRSA infection look like?

On the skin, MRSA infection may begin as redness or a rash with a pus-filled pimple or boil. It may progress to an open, inflamed area of skin that may weep pus or drain fluid. In some instances, it may appear as an abscess, a swollen, tender area, often with reddish skin covering. When the abscess is cut open or spontaneously bursts open, pus drains from the area. If the infection is severe or may be spreading into the blood (bacteremia), fevers and shaking chills may occur.

A woman with a bandaged arm rests in a hospital bed while wearing a surgical mask.

What are the risk factors for MRSA infections?

People with higher risk of MRSA infection are those with skin breaks (scrapes, cuts, or surgical wounds) or hospital patients with intravenous lines, burns, or skin ulcers. In addition, MRSA may infect people with weak immune systems (infants, the elderly, people with diabetes or cancer, or HIV-infected individuals) or people with chronic skin diseases (eczema and psoriasis) or chronic illnesses. People with pneumonia (lung infection) due to MRSA can transmit MRSA by droplets produced during coughing. Patients in health-care facilities are often in these risk categories, so special precautions recommended by CDC may be posted on a sign at the room entrance. Examples include "droplet precautions" -- if the patient has pneumonia, disposable masks, gowns, and gloves must be used by people who enter the room, and they must be taken off before leaving. "Contact precautions" may be posted recommending gowns and gloves only if the patient has skin infection. Precautions must be followed as posted by both health-care professionals and visitors to keep from spreading MRSA to other patients or people at risk of serious infection.

Abscess and cellulitis from a methicillin-resistant Staphylococcus aureus (MRSA) hand infection.

What are the signs and symptoms of a MRSA infection?

The incubation period (time between infection and start of symptoms) is variable and may depend on the particular strain of MRSA and the person's immunity. Most MRSA infections are skin and soft tissue infections that produce the following signs and symptoms:

  • Cellulitis, an infection of the skin or the fat and tissues under the skin, usually starting as small red bumps in the skin. It includes redness, swelling of the tissues, warmth, and tenderness.
  • 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)
  • Rash or skin redness (skin appears to be reddish or have red-colored areas)

All of these skin infections are painful.

A major problem with MRSA (and occasionally other staph infections) is that occasionally the skin infection can spread to almost any other organ in the body. When this happens, it is a deep or invasive infection that can spread to the blood and infect internal organs. MRSA infections can cause complications such as infection of heart valves (endocarditis), gangrene or death of the soft tissues (necrotizing fasciitis), and bone or joint infections (osteomyelitis or septic arthritis). This can be deadly. Fever, chills, low blood pressure, joint pains, severe headaches, shortness of breath, and rash over most of the body are symptoms of sepsis (blood poisoning), which requires emergency medical attention.

A man opens a door using the door handle. MRSA transmission can occur with objects such as door handles, floors, sinks, or towels that have been touched by a MRSA-infected person or carrier.

Is a MRSA infection contagious?

MRSA skin and soft tissue infections can be contagious or spread from person to person by contact with the skin, pus, or infected body fluids of a person who has MRSA. Some people may be "carriers" of MRSA. In other words, the bacteria lives on their skin or nostrils. It may cause no problems, or it may cause infections on that person's body or be transmitted to other people. It is not unusual for people in the community who are in frequent close contact with or who live with a person who has MRSA to also become carriers of MRSA. MRSA is very common in the community, especially in children and even pets.

How is a 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 from 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 breaks in the skin such as psoriasis (a chronic inflammatory skin disease with dry patches, redness, and white scales), MRSA (or any S. aureus) may proliferate. Many otherwise healthy people, 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 families, school team players (like football players or wrestlers), dormitory residents, and armed-services personnel in constant close contact.

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An illustration shows a doctor taking a sample of pus from a wound to have it tested for MRSA.

What tests do medical professionals use to diagnose a MRSA infection?

Most doctors start with a complete history and physical exam of the patient to identify any skin changes that may be due to MRSA, especially if the patient or caretaker mentions a close association with a person who has been diagnosed with MRSA. If possible, a sample of pus from a wound, blood, or urine is sent to a microbiology lab and cultured for S. aureus. Deep infections (such as bone) may require removal of a piece of tissue for testing (biopsy). If S. aureus is isolated (grown on a petri plate), the bacteria are then exposed to different antibiotics, including methicillin. S. aureus bacteria that grow well when methicillin is in the culture are termed MRSA, and the patient is diagnosed as MRSA-infected. Often there is no material to culture, and doctors treat the person with antibiotics that kill MRSA as well as more common bacteria until more information is available. This is called empiric therapy, meaning that doctors make their best guess on what bacteria are likely to be the cause of infection, until the bacteria have been definitively identified.

Some hospitals may screen patients for carrying MRSA, so that precautions can be taken to avoid spreading MRSA. The same procedure is done by swabbing the skin or inside the nose. These tests help distinguish MRSA infections from other skin changes that often appear initially similar to MRSA, such as spider bites or skin changes that occur with Lyme disease. Many MRSA infections get mistaken for a spider bite. This can cause delayed or incorrect treatment and progression of the MRSA infection.

There are rapid screening tests that can detect the presence of MRSA DNA material (polymerase chain reaction, PCR) in a blood sample in as little as two hours. The test is able to determine whether the genetic material is from MRSA or from less dangerous forms of staph bacteria. It may allow hospitals to start precautions early. It may also allow doctors to quickly tailor the antibiotics to only what is needed; this reduces unnecessary antibiotic use and helps reduce antibiotic resistance. It also may reduce side effects and costs of unnecessary antibiotics. These tests cannot be used alone for the diagnosis of a MRSA infection. They do not provide important details about the antibiotics to which the specific strain is susceptible.

An at-home nurse caregiver wraps a woman's leg wound with a bandage.

What types of doctors treat MRSA infections?

Since MRSA can affect any organ, different doctors may be involved in caring for someone with MRSA. Most surgeons and primary-care doctors, such as family practice specialists, pediatricians, internists, and emergency-care doctors, can treat MRSA infections. Complicated or deep MRSA infections are often treated by an infectious-diseases specialist who is consulted by another doctor. A pulmonologist (lung specialist) may help to treat patients with MRSA pneumonia. A cardiologist (heart specialist) may help to diagnose MRSA infection of the heart valves. Specialist surgeons may be needed to treat deep MRSA infections in different parts of the body, such as an orthopedist (bone surgeon), podiatrist (foot surgeon), vascular (blood vessel surgeon), or cardiovascular (heart) surgeons.

How should caregivers treat MRSA patients at home?

The CDC states that healthy caregivers are unlikely to become infected while caring for MRSA patients at home. Patients with MRSA and their caregivers should do the following:

  • Clean hands often, especially before and after changing wound dressings or bandages.
  • Keep any wounds clean and change bandages as instructed until healed.
  • Avoid sharing personal items such as towels or razors.
  • Wash and dry clothes and bed linens with detergent and the temperatures recommended on the labels. Cold water is adequate to remove germs if an item cannot be washed warm.
  • Tell health-care providers that the person has MRSA. This includes home health nurses and aides, therapists, and personnel in doctors' offices.
  • Follow all other instructions given by the doctor.

Quick GuideMRSA Infection: Causes, Symptoms, and Treatment

MRSA Infection: Causes, Symptoms, and Treatment
A doctor tends to a patient's MRSA infection.

What is the treatment for a MRSA infection?

  • The main treatment for boils and abscesses is incision and drainage. Antibiotics may not be needed if the infection is mild and the pus is drained.
  • If antibiotic treatment is needed, it is usually empiric (based on the physician's best guess). Treatment can be made more precise if a pus sample can be sent to the laboratory. When the tests are run to determine that the staph bacteria isolated from a given patient are methicillin-resistant, they also provide valuable information about which antibiotics can successfully kill the bacteria (its susceptibility profile).

Fortunately, many MRSA infections can be treated by a common and long-standing antibiotic, vancomycin (Vancocin and generic brands), and it is included in most empiric treatment regimens. Newer drugs are also available, although some are much more expensive: ceftaroline (Teflaro), linezolid (Zyvox), daptomycin (Cubicin), dalbavancin (Dalvance), telavancin (Vibativ), and others. Only linezolid comes in a pill in addition to intravenous (IV) solution. Moderate to severe infections need to be treated by IV antibiotics, usually given in the hospital setting and completed at home with a home health agency.

Less serious infections are often susceptible to trimethoprim-sulfamethoxazole (Bactrim), doxycycline (Vibramycin), and clindamycin (Cleocin), all of which come in an oral form as well as IV. Rarely, some strains have become resistant to vancomycin (vancomycin-resistance, vancomycin-resistant Staph aureus, VRSA); this may require combinations of antibiotics.

View MRSA Slideshow
A lab test of antibiotic tablets and resistant bacteria inside a petri dish.

What is the treatment for a MRSA infection? (Continued)

The CDC recommends clinicians use the 2011 guidelines published by the Infectious Diseases Society of America (IDSA) that detail treatments. The 38-page set of guidelines can be found at http://www.idsociety.org/
uploadedFiles/IDSA/Guidelines-Patient_Care/PDF_Library/MRSA.pdf. Since MRSA is resistant to multiple antibiotics, the treatment will depend on the specific MRSA bacteria that is cultured from each patient. The doctor will choose antibiotics that the laboratory reports as susceptible on the resistance test they perform on each culture.

Some people think they are "cured" after a few antibiotic doses and stop taking the medicine. Others may start forgetting to take it once they don't feel sick and get back to normal activity. This is bad because there may be bacteria left that start the infection up again, spread to other parts of the body, and are exposed to low antibiotic doses. Low antibiotic exposures give MRSA time to become resistant to the medicine. If the infection comes back, it may be worse and even harder to treat. In fact, this is howS. aureus and other bacteria became "superbugs." Anyone treated with antibiotics should take the entire course of the antibiotic as directed by their doctor. Setting up reminders for yourself as soon as you start on treatment helps keep you on track for success.

A doctor consults with a MRSA patient in the hospital.

What is the prognosis of a MRSA infection?

The prognosis of MRSA infections depends on how severe the infection is, the overall health of the patient, and how well the infection responds to treatment. Mild to moderate skin infections (boils, small abscesses) in patients with otherwise good health almost always have a good prognosis with full recovery if treated appropriately. However, patients with more severe infection and/or additional health problems (for example, diabetes, immunocompromised status, infected trauma wound), or those who get MRSA while in the hospital for another problem, have a prognosis from good to poor. MRSA pneumonia or sepsis has a death rate of about 20%. In addition, patients who are treated and do well still have a high risk of recurrent infection that may vary from 20%-40%. In addition, treatment with multiple antibiotics has its own risks. Drug reactions can occur. Killing of "friendly flora" (normal protective bacteria) in the bowel can lead to other infections such as pseudomembranous colitis caused by Clostridium difficile.

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A man gets his finger cleaned and bandaged to prevent infection.

How can people prevent a MRSA infection?

The best way to avoid MRSA infection is to avoid making direct contact with skin, clothing, and any items that come in contact with people who have MRSA. Because you never know where MRSA can be, basic precautions against any infections are most practical. Treat and cover (for example, antiseptic cream and a Band-Aid) any skin breaks or wounds. Pay attention to cleanliness. For example, wash hands with soap after toilet use. Soap makes dirt and bacteria slippery, and rubbing under water removes them. Alcohol-containing hand sanitizers are very effective if hands are not obviously dirty and you just need a quick sanitizing. Clothes that may have come in contact with MRSA are effectively treated by washing with detergent; cold water is as good as hot. Frequent cleaning of living areas also helps, especially the bathroom and kitchen.

Pregnant women should consult with their doctors if they are infected or are carriers of MRSA. In 2007, the first incidence of MRSA in a pet was recorded. 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.

The CDC does not recommend screening everyone 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. One study showed that the number of infections with both HA-MRSA and CA-MRSA dropped from 2005-2008, and authorities speculate that such drops are due to infection-control measures in hospitals and better home-care measures.

A group of doctors rush to help a sick patient.

What are the potential complications of a MRSA infection?

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 (pneumonia), necrotizing fasciitis, osteomyelitis, and sepsis (blood poisoning). Early diagnosis and treatment usually result in better outcomes and reduction or elimination of further complications.

Quick GuideMRSA Infection: Causes, Symptoms, and Treatment

MRSA Infection: Causes, Symptoms, and Treatment
CDC statistics on the number of U.S. superbug infections.

What is a superbug?

The term superbug is a nonspecific word that is used to describe any organism that is resistant to at least one or more commonly used antibiotics. The most common bacteria described as superbugs are the following:

  • MRSA (Staphylococcus aureus strains resistant to multiple antibiotics)
  • VRE (Enterococcus species resistant to the antibiotic vancomycin)
  • PRSP (Streptococcus pneumoniae strains resistant to penicillin)
  • ESBL (Escherichia coli and similar bacteria that are resistant to a certain category of antibiotics, such as cephalosporins)

Emerging superbugs may include multiple drug-resistant Clostridium difficile, VRSA (vancomycin-resistant S. aureus), and NDM Escherichia coli (New Delhi metallo-beta-lactamase resistant E. coli), and some strains of gonorrhea. In 2013, the CDC set up a superbug site listing 18 different genera and species as "threats" due to antimicrobial resistance. They are categorized as urgent, serious, and concerning according to their potential to cause serious health problems; MRSA is ranked as serious. The U.S. National Institutes of Health funds research to develop new diagnosis tools, treatments, and vaccines against superbugs, including MRSA.

Where are other MRSA information sources?

"Methicillin-resistant Staphylococcus aureus (MRSA) Infections," Centers for Disease Control and Prevention (CDC)

"Healthcare-Associated Infections (HAI)," CDC

Reviewed on 6/30/2017
References
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Baorto, Elizabeth P. "Staphylococcus aureus Infections.: Medscape.com. Apr. 27, 2016. <http://emedicine.medscape.com/article/971358-overview>.

Cheung, G., J. Hwang-Soo, and M.O. Chattergee. "Phenol-soluble modulins -- critical determinants of staphylococcal virulence." FEMS Microbiol Rev 38.4 (2014): 698-719.

Herchline, Thomas E. "Staphylococcal Infections." Medscape.com. Apr. 25, 2016. <http://emedicine.medscape.com/article/228816-overview>.

Kallen, A.J., S. Bulens, A. Reingold, et al. "Health Care-Associated Invasive MRSA Infections, 2005-2008." JAMA 304 (2010): 641-648.

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