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MRSA: Methicillin Resistant Staphylococcus aureus

About MRSA

The Question


S. aureus



Is MRSA dangerous?



The Question: "I am a student enrolled in a nursing program. Recently I heard nurses referring to a patient in ICU that he has "MRCA", or something that sounds like that. After asking a couple of them what disease is that, and getting no reply, I was wandering if you could tell me what kind of diseases is that?"

Dr. Keti:
February 24, 2003

MRSA stands for Methicillin Resistant Staphylococcus aureus (MRSA) infections. It is simply a strain of Staphylococcus, which is resistant to the usual antibiotics. However, there are other antibiotics that are effective treating this strain of bacterium.

Until recently, methicillin-resistant Staphylococcus aureus (MRSA) was rare outside of hospitals, and the infections with this type of pathogen appeared to really take off in the last decade.

Some recent studies suggest that if there is screening of all patients before entering the hospital wards this community-acquired form of the infection can be detected.
It can appear in patients with no identified risk factors, i.e. patients that appear to have no underlying illness, or patients that haven't been recently hospitalized or receiving antibiotics (1)

About the Staphylococcus aureus
S. aureus is an aerobic or facultative anaerobic bacterium. It appears as gram positive clusters (staphylo means grapes in Greek) on Gram stain(p1) and expresses a variety of extra cellular proteins and polysaccharides, some of which are correlated with virulence. S. aureus is coagulase positive. (7)

Staphylococcus aureus, is a bacterium that is frequently found on the skin and in the nose of healthy people, i.e. in about 20-40% of the normal population and in almost all children (3).
S. aureus normally can be also found in the lower colon of humans. This bacterium is prevalent (up to 67 %) on vulvar (female genital) skin and is extremely common (80% to 100%) on the skin of patients with certain dermatological diseases such as atopic dermatitis, but the reason for this finding is unclear.

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Staphylococci can cause many forms of infection like superficial skin lesions (boil, sty) and localized abscesses in other sites, deep-seated infections, such as osteomyelitis and endocarditis and more serious skin infections (furunculosis). Antibodies will neutralize staphylococcal toxins and enzymes, but vaccines are not available.

S. aureus is a major cause of hospital acquired (nosocomial) infection of surgical wounds and, with S. epidermidis, causes infections associated with indwelling medical devices (catheters).
It also causes food poisoning by releasing enterotoxins into food and causes Toxic Shock Syndrome(TSS) by release of super antigens into the blood stream.

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S. aureus expresses many potential virulence factors, such as surface proteins that promote colonization of host tissues, factors that may inhibit phagocytosis (capsule, immunoglobulin binding protein A), or toxins that damage host tissues and cause disease symptoms. Coagulase-negative staphylococci are normally less virulent and express fewer virulence factors.

Although the first report of a penicillin-resistant strain of S. aureus is believed to be published in 1945,(5) Some recent studies suggest that if there is screening of all patients before entering the hospital wards this community-acquired form of the infection can be detected.
MRSA can appear in patients with no identified risk factors, i.e. patients that appear to have no underlying illness, or patients that haven't been recently hospitalized or receiving antibiotics (1)
The National Nosocomial Infections Surveillance system (NNIS) reports an increasing trend of MRSA, such as 40% increase in resistance in 1999 in comparison to 1994-1998 data (5).

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Methicillin Resistant S. aureus (MRSA) first emerged in the United Kingdom in the early 1960s. (2)
Recent outbreaks in Japan, suggest that a methicilline resistant strain of staphylococcus aureus (MRSA) appeared because several antibiotics of the beta-lactam system had been used frequently in Japan during the 1980s.

According to one Finish Study by Saara Salmenlinna,* Outi Lyytikäinen,* and Jaana Vuopio-Varkila*
*National Public Health Institute, Helsinki, Finland(4)
"MRSA is defined as community acquired if the MRSA-positive specimen was obtained outside hospital settings or within 2 days of hospital admission, and if it was from a person who had not been hospitalized within 2 years before the date of MRSA isolation." The study believes that nosocomial MRSA strains in the community, including nursing homes and other non-acute care facilities, may be transmitted by discharged patients and health-care workers. None of the strains identified in this study, were multi resistant. Interestingly, the population-based data suggested that community-acquired MRSA might arise de novo. In Finland, the prevalence of MRSA has remained low, although several hospital epidemics have occurred in the last decade.

MRSA is now endemic in many hospitals, and is one of the leading causes of nosocomial pneumonia and surgical site infection and the second leading cause of nosocomial blood stream infections (6).

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Is MRSA dangerous?
Staph bacteria are one of the most common causes of skin infection in the United States, and are a common cause of pneumonia and bloodstream infections. According to CDC, Staph and MRSA infections are not routinely reported to public health authorities, so a precise number is not known.
The Association of Medical Microbiologists (AMM), believes that this bacterium is usually confined to hospitals and in particular to vulnerable or debilitated patients, including patients in intensive care units, burns units, surgical and orthopedic wards. In addition some nursing homes have experienced problems with this bacterium. The hospital staff, unless suffering from a debilitating disease is in no health danger. AMM does not recommended that the friends or family of a patient take any additional or special precautions or stop contacts altogether. (8)

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For those who work in hospital, practicing good hygiene, keeping hands clean by washing thoroughly with soap and water, as this is the single most important infection control measure, keeping cuts and abrasions clean and covered with a proper dressing until healed, using a moisturizer to prevent cracking, and using gloves to avoid contact with wounds or material contaminated from wounds is highly recommended preventive measures.

Patients diagnosed with MRSA should be isolated in a separate room, referred as contact isolation, the room should be regularly damp dusted, or the patients should be nursed in a special ward away from other patients. To prevent this organism from spreading keeping the patients' door closed at all times and wash hands always whenever you leave the room.

Antibiotics, e.g. mupirocin, applied inside the nose, as well as washing, bathing and hair washing with disinfectants e.g. chlorhexidine. The antibiotics that are used to treat MRSA are not just expensive, but may be toxic and have to be given by intravenous infusion. Patients infected with MRSA must therefore be treated in hospital. Accordingly, when such a patient is discharged from hospital, his or her room should be cleaned thoroughly and all linen and other clinical waste disposed of in designated bags.

The drug of choice for MRSA is Vancomycin, alternative antibiotics include linezolid and quinupristin/dalfopristin. Rifampin and trimethroprim-sulfamethoxazole (TMP-SMX) are used in combination with other antibiotics (6).

In addition to the above mentioned measures, active surveillance to control spread of MRSA is highly recommended, i.e. in high-risk populations, routine surveillance cultures done on admission and weekly there-after surveillance, as well as keeping good patient's record all the time, greatly assist infection control professionals in tracking MRSA cases.

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References and Links

Picture of S. aureus

pslgroup.com (2)

UC Davis Medical Center (3)


MRSA-By Stephanie Wise,(5)

CDC- article(6)


Association of Medical Microbiologists(8)