MRSA (Methicillin-Resistant Staphylococcus aureus) Infections
Medical Author: Charles Davis, MD, PhD
Medical Editor: Melissa Conrad Stöppler, MD
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Superbug Staph Spread in Community
Medical Author: Melissa Conrad Stöppler, MD
Medical Editor:
Barbara
K. Hecht, PhD
 MRSA, or methicillin-resistant Staphylococcus aureus, is a bacterium that can
cause serious infections. It is resistant to numerous antibiotics of the
beta-lactam family, including methicillin and penicillin.
MRSA belongs to the large group of bacteria known as
Staphylococci, often referred to as Staph. About 25%-30% of all people have Staph
within the nose, but it normally does not cause an infection. In contrast, only about 1% of the
population have MRSA.
Infections with MRSA are most common in
hospitals and other institutional health-care settings, such as nursing homes,
where they tend to strike older people, those who are very ill, and people with a
weakened immune system. In health-care settings, MRSA is a frequent cause of
surgical wound infections, urinary
tract infections, bloodstream infections (sepsis), and pneumonia.
MRSA outbreaks, however, are appearing increasingly in the
community. Infections can occur in people who have not been hospitalized or had a
medical procedure performed in the past year, and who do not have immune
deficiency. These infections are termed community-associated MRSA infections
(CA-MRSA).
The U.S. Centers for Disease Control and Prevention (CDC) estimates that about 12% of
MRSA infections are now community-associated, but this percentage can vary by
community and patient population.
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What is methicillin-resistant Staphylococcus aureus MRSA?
MRSA stands for methicillin-resistant Staphylococcus aureus (S. aureus)
bacteria. This organism is known for causing skin infections in addition to many
other types of infections. There are other designations in the scientific
literature for these bacteria according to where the bacteria are acquired by
patients, such as community-acquired MRSA (CA-MRSA), hospital-acquired or health-care-acquired MRSA (HA-MRSA), or epidemic MRSA (EMRSA). A number of Web and
popular press articles are titled or include the erroneous term "MRSA virus."
This is a misnomer; there is no contagious MRSA virus, and if readers examine
these articles, they may realize the content is usually about MRSA bacteria.
Although S. aureus has been causing infections (Staph infections) probably as
long as the human race has existed, MRSA has a relatively short history. MRSA
was first noted in 1961, about two years after the antibiotic methicillin was
initially used to treat S. aureus and other infectious bacteria. The resistance
to methicillin was due to a penicillin-binding protein coded for by a mobile
genetic element termed the methicillin-resistant gene (mecA). In recent years,
the gene has continued to evolve so that many MRSA strains are currently
resistant to several different antibiotics such as penicillin, oxacillin, and
amoxicillin (Amoxil, Dispermox, Trimox). HA-MRSA are often also resistant to tetracycline (Sumycin), erythromycin (E-Mycin, Eryc, Ery-Tab, PCE, Pediazole, Ilosone), and
clindamycin (Cleocin). In 2009, research showed that many antibiotic-resistant genes and
toxins are bundled and transferred together to other bacteria, which speed the
development of toxic and resistant strains of MRSA. S. aureus is sometimes
termed a "superbug" because of its ability to become resistant to several
antibiotics. Unfortunately, MRSA can be found worldwide.
What are the signs and symptoms of MRSA infection?
Most MRSA infections are skin infections that produce the following signs and
symptoms:
- cellulitis (infection of the skin or the fat and tissues that lie
immediately beneath the skin, usually starting as small red bumps in the skin),
- boils (pus-filled infections of hair follicles),
- abscesses (collections of pus
in under the skin),
- sty (infection of eyelid gland),
- carbuncles (infections
larger than an abscess, usually with several openings to the skin),
and
- impetigo (a
skin infection with pus-filled blisters).
One major problem with MRSA is that
occasionally the skin infection can spread to almost any other organ in the
body. When this happens, more severe symptoms develop. MRSA that spreads to
internal organs can become life-threatening. Fever, chills, low blood pressure, joint pains, severe headaches, shortness of breath, and "rash over most of the body" are symptoms that need immediate medical attention, especially when
associated with skin infections. Some CA-MRSA and HA-MRSA infections become severe, and complications such as endocarditis, necrotizing fasciitis, osteomyelitis, sepsis, and death may occur.
What does MRSA look like?
On the skin, it may begin as a reddish lesion that looks like a pimple or small boil. Often it progresses to an open, inflamed area of skin
(as pictured below) that may weep pus or drain other similar fluid. See the first Web citation for more MRSA pictures.
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| What does MRSA look like? |
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