MRSA

Community–Acquired Methicillin–Resistant
Staphylococcus Aureus (CA-MRSA)

Staph infections are caused by a common bacteria carried on the skin or in the nose of a high
percentage of individuals. In the simplest form, it causes pimples and boils but they can enlarge to
abcesses or even invade the blood stream to infect the heart or lungs.

Over the years, Staph bacteria have developed resistance to penicillin (PRSA) and methicillin
(MRSA). MRSA was recognized in the early 1960’s but it has been limited to hospitals and
institutional settings until recently. Over the past 6 years a new genetic strain of MRSA (USA 300)
has emerged in the Atlanta area. It caused 63% of Staph infections in one recent study. Its
prevalence has forced doctors to re-evaluate how they handle these infections. They are now
designated CA-MRSA (community-acquired methicillin–resistant Staphylococcus Aureus).

Two main problems that CA-MRSA presents to patients and physicians are 1) increased virulence
leading to more serious infection and 2) resistance to the commonly used antibiotics. Skin
infections with CA-MRSA often have black centers causing misdiagnosis as spider bites. This may
be caused by a new toxin (Panton-Valentine leukocidin) that causes white cell destruction and tissue
death. CA-MRSA is usually resistant to cephalosporins (eg. Keflex), fluoroquinolones (eg. Levaquin)
and penicillins (eg. Augmentin). They are sensitive to sulfa drugs and tetracyclines but prospective
studies of the effectiveness of these drugs have not been done. Newer drugs are promising.

Containing these infections require everyone’s best efforts. Patients must learn how to handle minor
lesions to prevent them from getting worse. They must learn meticulous hygiene when the infections
are present and when they are healed.

Simple incision and drainage may be sufficient for isolated abcesses but appropriate antibiotics may
be needed for more complex situations. These include trimethoprim-sulfa (ie: BactriM) or
doxycycline as well as others. Recurrent infections will likely require infectious disease expertise.
Culture and sensitivity studies will be needed more often to differentiate which Staph is involved.
There have been severe infections due to CA-MRSA including deaths but CA-MRSA can be controlled
when common sense and available therapeutic approaches are used. Click here for more
information on home treatment guidelines.

References

Moellering, R.C, Jr. The Growing Menace of Community-Acquired Methicillin-Resistant
Staphylococcus Aureus. Ann Internal Med. 2006; 144:368-370.

www.cdc.gov . CDC web site. Search A to Z Index for MRSA.

www.health.state.ga.us. Georgia Division of Public Health web site. “Important information about
Methicillin-Resistant Staphylococcus aureus (MRSA)".

www.lapublichealth.org. Los Angeles Department of Public Health web site. Search “Programs” then
select “Acute Communicable Disease Control”.

Updated June, 2008

M.P. Dailey, M.D. and D.L. Dickensheets, M.D.