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Update on antibiotic-resistant Staph aureus
New
threats within the community
Staphylococcus
aureus, or “staph” as it is sometimes called, is a common
bacterium found on the skin or in the nose of ~25-30% of humans.
While it is usually harmless, in certain instances it may cause
moderate to severe skin infections. Less commonly, it causes more
serious systemic infections e.g., bloodstream, surgical wound
and pneumonia requiring hospitalization. One group of staph known
as MRSA,(methicillin-resistant Staphylococcus aureus) was
first identified in the 1960’s, and is now prevalent in most hospitals.
The organisms are resistant to multiple antibiotics (specifically,
all antibiotics known as beta lactams, as well as other antibiotic
families), and are therefore cause for considerable concern. Because
of resistance, vancomycin has often been the only drug able to
successfully treat these MRSA infections.
A newer
form of staph infection, known as CA-MRSA (for community-acquired,
or community-associated Staphylococcus aureus) has appeared
with increasing frequency and is now epidemic within certain community
populations. Whereas hospital MRSA is almost always found in persons
with established risk factors associated with prior medical treatment,
these are not present in CA-MRSA. Today, in the U.S. a little
more than 10% of all MRSA infections are CA-MRSA. This form causes
serious skin and soft tissue infections in otherwise healthy persons
who have not been recently hospitalized or undergone invasive
medical procedures. Hospitalization is required in approximately
one out of five cases. CA-MRSA has been identified most frequently
among specific populations, including prisoners, athletes, children,
men who have sex with men, military recruits, Pacific Islanders,
Alaskan Natives and Native Americans.
A major
difference between the two types of MRSA is that the community
form (CA-MRSA) possesses a potent toxin called Panton-Valentine
leukocidin, which attacks infection-fighting white blood cells
called leukocytes. The most serious form of CA-MRSA infection
causes necrotizing
fasciitis, a severe, rapidly progressing and life-threatening
skin infection. The CA-MRSA are genetically distinguishable from
hospital associated MRSA.
In the
US, two clones (strains) of staph, called USA300 and USA400, are
associated with the community MRSA (CA-MRSA). USA300 has emerged
as the most prominent clone and is not found among hospital strains.
It was not observed before the year 2000, when multiple other
clones existed.
Treating
MRSA. Treatment of MRSA skin infections is challenging. In
some patients, skin ointments containing antibiotics, such as
mupirocin or fusidic acid, can be used, but resistance to these
can develop. Beta-lactam antibiotics (i.e., methicillin and oxacillin),
which are typically used to treat common Staph aureus infections
(such as furuncles, abscesses, and cellulitis), are ineffective.
Unlike hospital MRSA, which is resistant to multiple classes of
antibiotics, (including macrolides, aminoglycosides, fluoroquinolones,
tetracyclines and lincosamides), CA-MRSA is still susceptible
to several antibiotic classes outside of the beta-lactam group
(e.g., clindamycin).
In the
hospital, because of multidrug resistance, intravenous vancomycin
has become the drug of choice. Except for sporadic cases of vancomycin-resistant
MRSA (VRSA), all MRSA are susceptible to this antibiotic. Unfortunately,
the increasing use of vancomycin threatens to increase the VRSA
problem.
Prevention
The spread
of skin MRSA infections occurs most frequently through close,
skin-to-skin contact (such as that found in contact sports), through
contact with skin wounds (cuts, abrasions) and through contact
with contaminated items, where staph can survive for 24 hours
or more. The organisms can enter healthy, intact skin. Crowded
living conditions and poor hygiene are factors which play a role
in its spread. Currently, the only known means of prevention is
through the following:
- Prudent
hygiene measures involving hand washing
- Proper wound care, including
proper disposal of bandages, and
- Avoidance of sharing certain
personal items such as towels and razors. Shared exercise equipment
should be wiped down between users.
For more
information on the various forms of MRSA, the risk factors involved
and prevention advice, visit Centers for Disease Control: http://www.cdc.gov/ncidod/hip/aresist/ca_mrsa.htm
Also see:
APUA Newsletter, Focus CA-MRSA www.tufts.edu/med/apua/Newsletter/APUA_v21n2.pdf
Research
CA-MRSA
and Sports:
Recurring
Methicillin-resistant Staphylococcus aureus Infections
in a Football Team
Methicillin-Resistant
Staphylococcus aureus Infections Among Competitive Sports
Participants --- Colorado, Indiana, Pennsylvania, and Los Angeles
County, 2000--2003
CA-MRSA
and Correctional Facilities:
Methicillin-Resistant
Staphylococcus aureus Infections in Correctional Facilities
— Georgia, California, and Texas, 2001–2003 (see page 12)
Antibiotics
and MRSA:
Antibiotic
Selection for Infections Involving Methicillin-Resistant Staphylococcus
aureus
What
does CA-MRSA look like?
Digital
photographs of skin infections and wounds caused by community-associated
methicillin resistant Staphylococcus aureus (MRSA/Staph).
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