Alana Arnold, PharmD
Infectious Disease Specialist
Children's Hospital Boston
Definition - CA vs HA MRSA
The adaptive potential of the microbial world
is such that for each new antibiotic that is
introduced, several escape mechanisms are
The action of antibiotics and resistance are
linked like light and shadow: one does not
exist without the other.
3 Waldevogel, NEJM, 1999
aureus (MRSA) is a bacterium responsible
for difficult-to-treat infections in humans.
MRSA is by definition a strain of
Staphylococcus aureus that is resistant to a
large group of antibiotics called the beta-
lactams, which include the penicillins and the
Hospital–associated strains of S. Courtesy of the CDC
aureus still cause about 85% of all This electron micrograph depicts
large numbers of Staphylococcus
MRSA cases. aureus bacteria, which were
found on the inside surface of a
Hospital patients with S. aureus catheter. The sticky-looking
substance woven between the
infections are five times more likely to round cocci bacteria is known as
a “biofilm”. Biofilms help to
die in the hospital than are patients protect the bacteria.
without the infection.
Multi-drug resistant (MDR)
Vancomycin is one of the few
remaining treatments for HA-MRSA,
but it is no longer effective in every
5 case due to rising MICs.
From HA and CA-MRSA
1961 – MRSA first described
Until recently, most MRSA infections started in
hospitals, especially among surgery and
immunocompromised patients. (HA-MRSA)
In the 1990s, new strains of MRSA began to strike
healthy people in community settings. (CA-MRSA)
These two types of MRSA are now known as
hospital-associated MRSA (HA–MRSA) and
community-associated MRSA (CA–MRSA).
Staphyloccal bacteria that have become Courtesy of the CDC
resistant to beta-lactam antibiotics but NOT
multi-drug resistant (MDR).
Several antibiotics remain effective against
CA–MRSA, but it is an aggressive and
rapidly evolving form of S. aureus.
Usually appears as a skin infection, but it Cutaneous abscess
can spread quickly to a bloodstream caused by methicillin–
infection or a very serious form of resistant
pneumonia. Staphylococcus aureus
Prevalence is increasing!!
HA-MRSA in ICU patients
1989 = 27%
2005 = 60%
18 in 100,000 (Baltimore)
26 in 100,000 (Atlanta)
Some areas report > 10% incidence in ER skin infection visits
Review your antibiogram to assess prevalence in
Review patient’s risk factors for MRSA
Direct person to person contact
Sharing of towels or personal hygiene items
Drug use equipment
Transmission of Methicillin-Resistant
Staphylococcus aureus (MRSA)
Most MRSA infections occur through direct contact with
people or surfaces that carry the bacteria.
Staph bacteria enter the body through skin cuts or
abrasions and spread easily.
Approximately 25-30% of people carry S. aureus on
their bodies without becoming sick, but they can pass
the germ to others, who may become ill.
May occur in healthy persons without traditional HA-MRSA
associated risk factors.
CA–MRSA typically occurs in;
– Places where people have close contact, including childcare
centers, nursing homes, prisons.
– Certain populations (Pacific Islanders, Native Americans)
– Contact sports (football, rugby, wrestling)
– Sharing of towels, athletic equipment, personal items
– Poor personal hygiene
CA-MRSA and HA-MRSA
Infection Site Skin and soft tissue infections (SSTIs) Nosocomial pneumonia,
(pulmonary, bloodstream, urinary catheter-related, UTI,
infections much less common) bloodstream, or SSTI
Antimicrobial Usually susceptible to Bactrim, Vancomycin, Linezolid
doxycycline, clindamycin, rifampin Synercid, Daptomycin
Risk Factors Places where people have close Recent hospitalization or
contact-childcare centers, nursing surgery, history of recurrent
homes, and prisons. abscesses or recurrent skin
Certain populations (Pacific Islanders, infection, Long term care
Native Americans) facility resident, IV drug user,
Contact sports (football, wrestling) indwelling catheters, medical
conditions such as diabetes,
Sharing of towels, athletic equipment, HIV, renal failure
Poor personal hygiene
Commonly complain of infected pimples, spider
bites, or sores.
Usually minor carbuncles, furuncles, abscesses.
Can be more extensive cellulitis, deep-seated
abscesses, septic arthritis, pneumonia and sepsis.
Should be considered in the DDX of all SSTIs.
Aerobic cultures should be obtained on all open
lesions/ draining abscesses.
Some S. aureus infections can be treated
without antibiotics by surgically draining the
wound. Local incision and drainage and hot Cultured Staphylococcus
packs are first-line therapy for skin infections. aureus on agar plate.
Before prescribing an antibiotic, a doctor must
determine if MRSA bacteria are present.
Using the wrong drug delays treatment and
encourages the development of more resistant
Resistant to beta-lactam antibiotics
Retain susceptibility to many other classes of
antimicrobials such as;
– Tetracyclines (Doxycycline/Minocycline/Tigecycline)
HA-MRSA = MDR and only treated with vancomycin,
linezolid, daptomycin or Synercid
Abx based on culture confirmation and sensitivity
Close follow-up in 24-48 hrs
Clindamycin ~50% (in Boston area)
Clindamycin resistance is inducible – do not
use for empiric therapy
Tetracyclines – ?
Do not use if patients <8yrs of age
Vancomycin, linezolid, daptomycin and Synercid
Bactrim 12-20 mg/kg/day divided q8-12hr
Clindamycin 30 mg/kg/day PO divided q8hr
Doxycycline 4 mg/kg/day PO divided q12hr
Duration = 4 weeks
Vancomycin, linezolid, daptomycin and Synercid
JR is a 5 yr old boy with sulfa allergy who
presents to ER with skin lesion and fever
Would drained, culture done
Empiric therapy ?
MSSA or MRSA?
Insufficient evidence to support use of topical or
systemic antimicrobial therapy for eradicating MRSA
– Cochrane review of 6 trials with 384 participants
– Insufficient evidence to support the use of either topical or
– Potential for serious adverse events and development of
Per CDC and NEHC, it may be reasonable when pt
has multiple documented recurrences.
Per NEHC consider Hibiclens washes from neck
down x 5 days.
Isolation and Contact Precautions within health
Wash hands frequently and thoroughly.
Use a hand sanitizer when soap and water are
Keep skin cuts clean and covered.
Don’t touch another person’s skin wound or
Avoid sharing personal items, such as towels,
washcloths, and razors.
Routine cleaning of athletic equipment
Routine disinfection of countertops, exam tables
or other treatable surfaces.
All open wounds should be covered.