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Methicillin-resistant Staphylococcus Aureus

Methicillin-resistant Staphylococcus Aureus

What is going on in the body?

Methicillin-resistant Staphylococcus aureus, or MRSA, is a strain of the Staphylococcus aureus bacteria-commonly referred to as "staph"-that when it was first named, in the 1960's, was resistant to the effects of the antibiotic methicillin. Prior to that time, penicillin antibiotics had been used to successfully treat virtually all staph infections. However, in the late 1940s and throughout the 1950s, the staph bacteria began to develop resistance to penicillin. Researchers developed a new form of penicillin-methicillin-to counter this problem. Initially MRSA was found primarily in hospitalized patients. However, in the last three decades, MRSA has become resistant to more types of antibiotics, leaving fewer options to treat the infection. In addition, MRSA has become a more common cause of infections outside the hospital. These factors ahave lead some to call MRSA a "Super Bug." People often carry staph bacteria on their skin or in their nose. In fact, anywhere from 25 percent to 30 percent of the population is colonized, but uninfected, with the staph bacteria. A much smaller proportion of the population-approximately 1 percent-is colonized, but uninfected, with the methicillin-resistant strain of staph (MRSA). While colonized individuals may be uninfected and healthy, the fact that they are carrying the bacteria means they can spread it to others-primarily through bodily contact. In general, the bacteria are harmless unless they find a way into the body, via a cut or other wound for example. Normally, such an invasion causes only minor skin problems in healthy individuals, but people who are elderly, are already sick or who have a weakened immune system can become seriously ill since their body may not be able to tackle the bacteria. However, with MRSA becoming more resistant to more antibiotics, it has become increasingly dangerous to healthy individuals who contract the infection.

What are the signs and symptoms of the infection?

All infections from staph bacteria, whether or not it is a strain resistant to antibiotics, most commonly start as skin infections. It can begin as small red bumps that resemble pimples, boils or spider bites. It can also be swollen, warm or painful and have pus or other drainage. These infections can rapidly progress to deep, painful abscesses that require surgical draining. The bacteria may remain confined to the skin, but if they gain access to deeper parts of the body, the infection becomes potentially life-threatening. If it settles in bones, joints, surgical wounds, the bloodstream, heart valves, or lungs, it can cause serious or even fatal illness. The symptoms associated with these types of infections can include high fever, swelling, heat and pain around a wound, headache and fatigue, low blood pressure, among others. Because MRSA is a type of staph, the symptoms of an MRSA infection and the symptoms of an infection due to other staph are the same.

What are the causes and risks of the infection?

MRSA is spread the same way as other staph bacteria. That is, by direct skin-to-skin contact, such as shaking hands and wrestling, and by sharing items like towels and sports equipment. Poor hygiene practices and close living quarters also contribute to its spread. The majority of MRSA infections occur among patients in hospitals or other health care settings, but it is becoming more common in the community setting. According to the Centers for Disease Control and Prevention, a 2003 study suggested that 12 percent of clinical MRSA infections are community-associated, although this proportion varies by geographic region and population. Therefore, staph infections, including MRSA, occur most frequently among persons in hospitals and health care facilities, such as those in nursing homes and dialysis centers. These individuals often have weakened immune systems. This is known as health care-associated MRSA, or HA-MRSA. The main mode of transmission to other patients is through hands, especially health care workers' hands, which may become contaminated with MRSA bacteria by contact with infected or colonized patients. People who are otherwise healthy and who have not recently undergone a medical procedure or been hospitalized might also get an MRSA infection. These infections are referred to as community-associated MRSA, or CA-MRSA. These infections are usually skin infections. For example, students in high school or college who are involved in contact athletics, like football, may present with an infection if they come into contact with the bacteria and it gets into an open wound. One scenario for the transmission could involve drying off with a previously-used towel that has MRSA on it from another teammate who happens to be colonized, but uninfected, with MRSA. If an individual has a skin infection, it is important to know if it is from MRSA. Because special lab tests are needed to identify MRSA, a physician may initially treat the infection as if it were from a regular staph strain. The doctor may prescribe antibiotics that are not effective against MRSA. This delay in identifying MRSA infections and treating them effectively can result in prolonged illness and rare life-threatening illnesses in the blood, heart and bones.

What can be done to prevent the infection?

The best defense against acquiring an MRSA infection is to practice good hygiene. In the health care setting, appropriate hand hygiene, such as washing with soap and water or using an alcohol-based hand sanitizer, is critical to prevent the transmission of HA-MRSA. If proper hand hygiene is not performed, the bacteria can be spread when a health care worker touches patients after picking up the bacteria from another. Patients can help by asking all hospital staff to wash their hands before being touched. In the community setting, putting into practice a few common sense strategies will help prevent acquiring a CA-MRSA infection.
  • Keep hands clean by washing thoroughly with soap and water or using an alcohol-based hand sanitizer.
  • Keep cuts and scrapes clean and covered with a bandage until healed.
  • Also important is avoiding contact with other people's wounds or bandages or carefully wash hands after touching or dressing a wound.
  • Sharing personal items, such as towels, washcloths or razors, should also be discouraged.
  • Showering promptly after exercising is recommended, and items such as gym and sports equipment should be cleaned and disinfected before use.
  • Finally, wash dirty clothes, linens and towels with hot water and laundry detergent, using bleach if possible, and drying cloths on a hot setting helps kill bacteria.

How is the infection diagnosed?

To determine if an infection is caused by MRSA, a health care provider will take a sample of the infected area, usually with some sort of swab, and send it to a lab for microbiological analysis. The laboratory technician will first determine what type of bacteria is present. This is done by placing the sample in a dish of nutrients that encourages bacterial growth. The procedure can require as many as 48 hours for the bacteria to grow. If the technician identifies the bacteria as S. aureus, a second test is needed to determine if it is methicillin resistant, because under a microscope MRSA looks like any other kind of staph strain. Newer tests are becoming more widely available that can detect staph DNA in a matter of hours. Access to such technology is very helpful since it allows for the most appropriate treatment to be initiated as quickly as possible. In addition to a culture of the infected area, other tests may be performed. Physicians can request a sputum culture if pneumonia is suspected, a urine culture if a urinary tract infection is suspected or a blood culture to determine if any bacteria are present in the blood stream. Several criteria must be met for a physician to diagnose a case of CA-MRSA as opposed to HA-MRSA. Most of the criteria have to do with the patient not having had exposure to inpatient medical care at a hospital within the past year.

What are the long-term effects of the infection?

It is important that MRSA infections are treated since organ failure and death may result if left untreated. Even when treated, the outcome depends on the severity of the infection as well as the general condition of the person with the infection. It is also possible to have a staph or MRSA skin infection recur after it is cured. To keep this from happening, follow your health care professional's directions for treatment and adhere to prevention steps after the infection is gone. The majority of CA-MRSA infections are skin infections and soft tissue infections, like abscesses (local accumulations of pus anywhere in the body) or cellulitis (acute infection below the surface of the skin). But other skin conditions can be caused by MRSA, such as impetigo, folliculitis (hair follicle infection) or furunculosis (boils that persist for weeks or months). A very severe skin and tissue infection called necrotizing fasciitis, often referred to in news reports as "flesh-eating bacteria," is rare but can occur. Other serious complications of staph infections may include joint infections, necrotizing pneumonia or septicemia (blood poisoning). Pneumonia and blood poisoning from MRSA have high death rates.

What are the risks to others?

People who have skin infections should be very careful and take precautions to avoid spreading their infection to others. Since MRSA and other staph bacteria are spread by direct skin-to-skin contact and by contact with contaminated surfaces, several steps should be taken to reduce the risk of spreading staph or MRSA skin infections to others, such as family members, friends and colleagues at work.
  • Keep the wound covered, especially if the wound is draining or pus is present, to prevent contamination of other individuals or surfaces.
  • Use a clean, dry bandage and follow instructions from a health care provider on proper wound care.
  • Be certain to properly dispose of all dressings and tape contaminated with drainage from the infected site since the pus can contain the bacteria.
  • Keep hands clean by washing frequently with soap and warm water or by using an alcohol-based had sanitizer. This is particularly important after changing the bandage or touching the infected wound.
  • Also, do not permit others to use your personal items such as towels, washcloths, razors, clothing or uniforms that may have come into contact with the infected wound.
  • All soiled clothing should be washed thoroughly, with a mild bleach solution if possible, and dried using a hot setting.
  • Finally, notify all health care providers of the infection if they are treating an unrelated condition and are unaware of the wound.

What are the treatments for the infection?

Incision and drainage in a physician's office may be the only treatment necessary for localized staph skin infections. Draining of skin boils or abscesses should only be performed by a health care professional. Sometimes treatment requires the use of antibiotics. If antibiotics are needed, it is important to take all the prescribed doses since unfinished doses can lead to development of drug resistance of the bacteria. What antibiotic to administer depends upon the results of the bacteria culture grown in the lab. Both HA-MRSA and CA-MRSA still respond to certain medications, although the choices are very limited. In hospitals and other health care facilities, physicians generally rely on the antibiotic vancomycin to treat resistant germs. For infections acquired in the general community, MRSA may be treated with vancomycin or other antibiotics, such as trimethoprim-sulfamethoxazole, that have proved effective against particular strains. Another option for serious MRSA infections is linezolid. There is a risk that over time, more MRSA strains will become resistant to vancomycin, a phenomenon that is already being observed to some degree. To help reduce this threat, physicians may choose to drain an abscess first without using antibiotics, and will only prescribe antibiotics if the infection is not going away.

What are the side effects of the treatments?

The antibiotics used to treat MRSA infections can cause certain side effects. Vancomycin can lead to certain problems with the kidneys and also to low levels of a particular type of white blood cell called neutrophils. There have also been some reports of hearing loss associated with intravenously administered vancomycin, but most of these patients had kidney dysfunction or a pre-existing hearing loss, or were receiving treatment at the same time with another drug that also increased the risk of hearing side effects. Vertigo, dizziness and tinnitus, which is ringing in the ears, have been reported but are rare. The most common side effects associated with linezolid treatment include diarrhea, headache, nausea and vomiting. Other reported side effects have included fungal infection in the mouth and, in women, the vagina, high blood pressure, problems with digestion, itchy skin and tongue discoloration. Linezolid may also lead to low levels of platelets, which are small blood cells needed for normal clotting. However, this condition appears to be dependent upon the duration of therapy, generally at least two weeks. The platelet counts for most patients who develop this problem return to normal levels during follow-up.

What happens after treatment for the infection?

If the infection has not improved within a few days after beginning treatment, contact your health care professional.

How is the infection monitored?

Once cured, it is possible to have a staph or MRSA skin infection recur. To prevent this from happening, be vigilant about practicing good hygiene and look for any similar infections on your skin.

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