MRSA
Methicillin Resistant Staphylococcus Aureus 
Fact Sheet

What is Staphylococcus aureus?

Staphylococcus aureus, often referred to simply as "staph," are bacteria commonly carried on the skin or in the nose of healthy people. Occasionally, staph can cause an infection; staph bacteria are one of the most common causes of skin infections in the United States. Most of these infections are minor (such as pimples and boils) and most can be treated without antibiotics (also known as antimicrobials or antibacterials). However, staph bacteria can also cause serious infections (such as surgical wound infections and pneumonia). In the past, most serious staph bacteria infections were treated with a certain type of antibiotic related to penicillin. Over the past 50 years, treatment of these infections has become more difficult because staph bacteria have become resistant to various antibiotics, including the commonly used penicillin-related antibiotics (1). These resistant bacteria are called methicillin-resistant Staphylococcus aureus, or MRSA.

Where are staph and MRSA found?

Staph bacteria and MRSA can be found on the skin and in the nose of some people without causing illness. 

What is the difference between colonization and infection?

Colonization occurs when the staph bacteria are present on or in the body without causing illness. Approximately 25 to 30% of the population is colonized in the nose with staph bacteria at a given time (2).
Infection occurs when the staph bacteria cause disease in the person. People also may be colonized or infected with MRSA, the staph bacteria that are resistant to many antibiotics. 

Who gets MRSA?

Staph bacteria can cause different kinds of illness, including skin infections, bone infections, pneumonia, severe life-threatening bloodstream infections, and others. Since MRSA is a staph bacterium, it can cause the same kinds of infection as staph in general; however, MRSA occurs more commonly among persons in hospitals and healthcare facilities.
MRSA infection usually develops in hospitalized patients who are elderly or very sick or who have an open wound (such as a bedsore) or a tube going into their body (such as a urinary catheter or intravenous [IV] catheter). MRSA infections acquired in hospitals and healthcare settings can be severe. In addition, certain factors can put some patients at higher risk for MRSA including prolonged hospital stay, receiving broad-spectrum antibiotics, being hospitalized in an intensive care or burn unit, spending time close to other patients with MRSA, having recent surgery, or carrying MRSA in the nose without developing illness (3-6).

MRSA causes illness in persons outside of hospitals and healthcare facilities as well. Cases of MRSA diseases in the community have been associated with recent antibiotic use, sharing contaminated items, having active skin diseases, and living in crowded settings. Clusters of skin infections caused by MRSA have been described among injecting drug-users (7,8), aboriginals in Canada (9), New Zealand (10) or Australia (11,12), Native Americans in the United States (13), incarcerated persons (14), players of close-contact sports (15,16) and other populations (17-23). Community-associated MRSA infections are typically skin infections, but also can cause severe illness as in the cases of four children who died from community-associated MRSA (24). Most of the transmission in these settings appeared to be from people with active MRSA skin infections. 

How common is staph and MRSA?

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. Staph and MRSA infections are not routinely reported to public health authorities, so a precise number is not known. According to some estimates, as many as 100,000 persons are hospitalized each year with MRSA infections, although only a small proportion of these persons have disease onset occurring in the community. Approximately 25 to 30% of the population is colonized in the nose with staph bacteria at a given time (2). The numbers who are colonized with MRSA at any one time is not known. CDC is currently collaborating with state and local health departments to improve surveillance for MRSA. Active, population-based surveillance in selected regions of the United States is ongoing and will help characterize the scope and risk factors for MRSA in the community. 

Are staph and MRSA infections treatable?

Yes. Most staph bacteria and MRSA are susceptible to several antibiotics. Furthermore, most staph skin infections can be treated without antibiotics by draining the sore. However, if antibiotics are prescribed, patients should complete the full course and call their doctors if the infection does not get better. Patients who are only colonized with staph bacteria or MRSA usually do not need treatment. 

How are staph and MRSA spread?

Staph bacteria and MRSA can spread among people having close contact with infected people. MRSA is almost always spread by direct physical contact, and not through the air. Spread may also occur through indirect contact by touching objects (i.e., towels, sheets, wound dressings, clothes, workout areas, sports equipment) contaminated by the infected skin of a person with MRSA or staph bacteria. 

How can I prevent staph or MRSA infections?

Practice good hygiene

1. Keep your hands clean by washing thoroughly with soap and water

2. Keep cuts and abrasions clean and covered with a proper dressing (e.g., bandage) until healed

3. Avoid contact with other people’s wounds or material contaminated from wounds.

What should I do if I think I have a Staph or MRSA infection?

See your healthcare provider.

What is CDC doing to address MRSA in the community?

CDC is concerned about MRSA in communities and is working with multiple partners on prevention strategies.

• CDC is working with 4 states in a project to define the spectrum of disease, determine populations affected, and developing studies to define who is at particular risk for infection
• CDC is working with state health departments to assist in the development of surveillance systems for tracking MRSA in the community
• CDC is using the National Health and Nutritional Evaluation Survey (NHANES) to estimate the number of individuals in the United States who carry staph bacteria in their nose
• CDC works with laboratories across the country to improve the detection of MRSA through training personnel and use of appropriate testing methods
• CDC provides technical expertise to hospitals and state and local health departments on infection control in healthcare settings, including control of MRSA
• CDC laboratories are working to characterize the unique features of MRSA strains from the community.

References:
1. Lowry FD. Staphylococcus aureus infections. New England Journal of Medicine. 1998;339:520-32.
2. Kluytmans J, Van Belkum A, Verbrugh H. Nasal carriage of Staphylococcus aureus: epidemiology, underlying mechanisms, and associated risks. Clin Microbiol Rev. 1997;10:505-20.
3. Boyce JM. Methicillin-resistant Staphylococcus aureus. Detection, epidemiology, and control measures. Infect Dis Clinics of North Am. 1989;3:901-13.
4. Herwaldt LA. Control of methicillin-resistant Staphylococcus aureus in the hospital setting. Am J Medicine. 1999;106:11S-18S; discussion 48S-52S.
5. Asensio A, Guerrero A, Quereda C, Lizan M, Martinez-Ferrer M. Colonization and infection with methicillin-resistant Staphylococcus aureus: associated factors and eradication. Infec Control Hosp Epidemiol. 1996;17:20-8.
6. Mulligan ME, Murray-Leisure KA, Ribner BD, et al. Methicillin-resistant Staphylococcus aureus: a consensus review of the microbiology, pathogenesis, and epidemiology with implications for prevention and management. Am J Medicine. 1993;94:313-28.
7. Saravolatz LD, Markowitz N, Arking L, Pohloh D, Fisher E. Methicillin-resistant Staphylococcus aureus. Epidemiologic oberservations during a community-acquired outbreak. Annals of Internal Medicine. 1982;96:11-16.
8. CDC. Community-acquired methicillin-resistant Staphylococcus aureus infections—Michigan. MMWR. 1981;30:185-7.
9. Embil J, Ramotar K, Romance L, et al. Methicillin-resistant Staphylococcus aureus in tertiary care institutions on the Canadian prairies 1990-1992. Infection Control and Hospital Epidemiology 1994; 15:646-51.
10. Rings T, Findlay R, Lang S. Ethnicity and methicillin-resistant S. aureus in South Auckland. New Zealand Medical Journal 1998; 111:151.
11. Maguire GP, Arthur AD, Boustead PJ, Dwyer B, Currie BJ. Emerging epidemic of community-acquired methicillin-resistant Staphylococcus aureus infection in the Northern Territory. Medical Journal of Australia 1996; 1996; 164:721-3.
12. Collignon P, Gosbell I, Vickery A, Nimmo G, Stylianopoulos T, Gottlieb T. Community-acquired methicillin-resistant Staphylococcus aureus in Australia. Australian Group on Antimicrobial Resistance. Lancet 1998; 352:145-6.
13. Groos A, Naimi T, Wolset D, Smith-Johnson K, Moore K, Cheek J. Emergence of community-acquired methicillin-resistant Staphylococcus aureus in a rural American Indian community (Abstract 1230), 39th Annual Interscience Conference on Antimicrobial Agents and Chemotherapy, San Francisco, CA, 1999.
14. Methicillin-resistant Staphylococcus aureus skin or soft tissue infections in a state prison—Mississippi, 2000. MMWR 2001 Oct. 26. 50 (42); 919-922.
15. Lindenmayer JM, Schoenfeld S, O’Grady R, Carney JK. Methicillin-resistant Staphylococcus aureus in a high school wrestling team and the surrounding community. Archives of Internal Medicine 1998; 158:895-9.
16. Stacey AR, Endersby KE, Chan PC, Marples RR. An outbreak of methicillin- resistant Staphylococcus aureus infection in a rugby football team. British Journal of Sports Medicine 1998; 332: 153-4.
17. Kallen AJ, Driscoll TJ, Thornton S, Olson PE, Wallace MR. Increase in community-acquired methicillin-resistant Staphylococcus aureus at a Naval Medical Center. Infection Control and Hospital Epidemiology 2000; 21: 223-6
18. Hussain FM, Boyle-Vavra S, Bethel CD, Daum RS. Current trends in community-acquired methicillin-resistant Staphylococcus aureus at a tertiary care pediatric facility. Pediatric Infectious Disease Journal 2000; 19: 1163-6.
19. Feder HM, Jr. Methicillin-resistant Staphylococcus aureus infections in 2 pediatric outpatients. Archives of Family Medicine 2000; 1163-6.
20. Goetz A, Posey K, Fleming J, et al. Methicillin-resistant Staphylococcus aureus in the community: a hospital-based study. Infection Control and Hospital Epidemiology 1999; 20: 689-91.
21. Frank AL, Marcinak JK, Mangat PD, Schreckenberger PC. Community-acquired and clindamycin-susceptible methicillin-resistant Staphylococcus aureus in children. Pediatric Infectious Disease Journal 1999; 18:993-1000.
22. Price MF, McBride ME, Wolf JE, Jr., Prevalence of methicillin-resistant Staphylococcus aureus in a dermatology outpatient population. Southern Medical Journal 1998: 91:369-71.
23. Herold BC, Immergluck LC, Maranan MC, et al. Community-acquired methicillin-resistant Staphylococcus aureus in children with no identified predisposing risk. JAMA 1998; 279:593-8.
24. From the Centers for Disease Control and Prevention. Four pediatric deaths from community-acquired methicillin-resistant Staphylococcus aureus—Minnesota and North Dakota, 1997-1999. JAMA 1999; 282: 1123-5.

The Centers for Disease Control and Prevention (CDC) has received inquiries about infections with antibiotic-resistant Staphylococcus aureus (including methicillin-resistant S. aureus [MRSA]) among persons who have no apparent contact with the healthcare system. This fact sheet addresses some of the most frequently asked questions.