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Antimicrobial (Drug) Resistance

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Methicillin-Resistant Staphylococcus aureus (MRSA)

Transmission

Today, S. aureus has evolved to the point where experts refer to MRSA in terms ranging from a considerable public health burden to a crisis. The bacteria have been classified into two categories based on where infection is first acquired.

Hospital-Acquired (HA)-MRSA

HA-MRSA has been recognized for decades and primarily affects people in healthcare settings, such as those who have had surgery or medical devices surgically implanted. This source of MRSA is typically problematic for the elderly, for people with weakened immune systems, and for patients undergoing kidney dialysis or using venous catheters or prosthetics.

A study published in 2005 found that nearly 1 percent of all hospital in-patient stays, or 292,045 per year, were associated with S. aureus infection. The study reviewed nearly 14 million patient discharge diagnoses from 2000 and 2001. Patients with diagnoses of S. aureus infection, when compared with those without the infection, had about three times the length of stay, three times the total cost, and five times the risk of in-hospital death. Notably, the S. aureus infections in this hospital study resulted in 14,000 deaths.

Community-Associated (CA)-MRSA

CA-MRSA has only been known since the 1990s. CA-MRSA is of great concern to public health professionals because of who it can affect. Unlike the hospital sources, which usually can be traced to a specific exposure, the origin of CA-MRSA infection can be elusive. CA-MRSA skin infections are known to spread in crowded settings; in situations where there is close skin-to-skin contact; when personal items such as towels, razors, and sporting equipment is shared; when personal hygiene is compromised; and when health care is limited.

Outbreaks of CA-MRSA have involved bacterial strains with specific microbiologic and genetic differences from traditional HA-MRSA strains, and these differences suggest that community strains might spread more easily from person to person than HA-MRSA. While CA-MRSA is resistant to penicillin and methicillin, they can still be treated with other common-use antibiotics.

CA-MRSA most often enters the body through a cut or scrape and appears in the form of a skin or soft tissue infection, such as a boil or abscess. The involved site is red, swollen, and painful and is often mistaken for a spider bite. Though rare, CA-MRSA can develop into more serious invasive infections, such as bloodstream infections or pneumonia, leading to a variety of other symptoms including shortness of breath, fever, chills, and death. CA-MRSA can be particularly dangerous in children because their immune systems are not fully developed.

You should pay attention to minor skin problems—pimples, insect bites, cuts, and scrapes—especially in children. If the wound appears to be infected, see a healthcare provider.

Researchers continue to study information about these cases in an attempt to determine why certain groups of people become ill when exposed to these strains. Researchers also continue to try to understand why high-incidence areas may appear. For example, for unknown reasons, severe outbreaks have occurred in Alaska, Georgia, and Louisiana.

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Last Updated February 18, 2009

Last Reviewed February 18, 2009