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CommunityAssociated MRSA
Maha Assi, MD, MPH
MRSA Hits the Media
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October 16, 2007
Lead story on MRSA
“superbug killing
many in US”
MRSA Kills High School
Student
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17 year old Ashton
Bonds died of
disseminated MRSA
infection
Prompts closing of
school for cleaning
MRSA kills Football Player
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20 year old college football player who
developed a skin infection. He was seen and
treated with antibiotics. MRSA was not
suspected. He died within days of disseminated
CA-MRSA
CA-MRSA
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An Epidemic
A great deal of
media attention
Public concern
MRSA and the Media
How Common is CA-MRSA
colonization ?
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General population analysis of data from the
NHNES
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Colonized with Staph aureus 31.6%
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84 million
Colonized with MRSA 0.84%
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2 million
Annals of Internal Medicine. 2006 March 7;144(5):318-25
How common is disease due
to CA-MRSA?
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In 2005 in US 94,360 cases of invasive
MRSA infection with 18,650 deaths.
Of those, 14% were community-acquired
infections.
Traditional MRSA Risk
Factors
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Newborns, elderly, hospital workers, HD,
IVDU, Diabetics, patients with chronic
dermatitis
Hospitalized patients, antibiotic receipt,
chronic illness of any kind
Community-Associated MRSA
without Identifiable Risk
Factors
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Herold 1988- reported 25 fold increase in
MRSA colonization in children at a
Chicago Hospital
Adcock 1998-2 day care centers with from
3-24% colonization- 40% in children with
no contact with health care system
Deaths of 4 children in MN/ND 1999
Herold et al JAMA 1998:279:593-8
Adcock et al JID 1998:178:577-80
MMWR 1999;48:707-10
Community outbreaks
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Native and aboriginal communities
Sports teams
Child care centers
Military personnel
Men who have sex with men
Prison inmates and guards
Risk factors
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Skin trauma (e.g. lacerations, abrasions,
tattoos, injection drug use), cosmetic body
shaving, incarceration, sharing equipment
that is not cleaned or laundered between
users, and close contact with others who
have MRSA colonization or infection.
Animals can also carry MRSA and
function as a source of transmission.
What about me?
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Importantly, many patients with CA-MRSA
have no risk factors.
Is that all?
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CA-MRSA may cause disease without
previous nasal colonization, and/or favor
other sites of colonization over the nares
(such as the skin, throat, or
gastrointestinal tract).
The Molecular Biology of
MRSA
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Resistance to Penicillin=B-lactamases
Resistance to Methicillin=Penicillin binding
protein 2a (PBP 2a)
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Alterations in PBP 2a carried on SCCmec
Nosocomial MRSA=SCCmec II and III
 CA-MRSA=SCCmec IV
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The USA300 strain
Necrotizing pneumonia
caused by CA-MRSA
Outcomes in Patients Treated
for CA-MRSA
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33% nonresponse at day 30
Failure related to lack of I & D (p=.005)
Failure not associated with wrong
antibiotic choice
Trend for close contacts to develop a
similar infection by day 30
Clin Infec Dis. 2007;44:483-92
Eradication of MRSA
Colonization
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The role of decolonization in the control of
methicillin-resistant Staphylococcus
aureus (MRSA) spread is uncertain.
Decolonization does not appear to be
consistently effective for eliminating MRSA
carriage.
The optimal regimen and duration of
therapy for eradicating MRSA colonization
is uncertain.
Topical regimen
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Chlorhexidine washes
Mupirocin or Bactroban ointment applied
to nares with a cotton-tipped applicator
two to three times daily
Prevention of CA-MRSA
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Handwashing
Isolation
Decolonization
Vaccination??
Vaccine for Staph aureus
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Capsular polysaccharides serotypes 5 and 8
Conjugated with protein from Pseudomonas
exotoxin
Randomized trial in hemodialysis patients
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Partial immunity, decreased Staph aureus
bacteremias at 40 weeks
By 54 weeks no difference
?booster doses
Passive immunization