Community-Associated MRSA

Maha Assi, MD, MPH

MRSA Hits the Media

October 16, 2007 Lead story on

MRSA “superbug killing

many in US”

MRSA Kills High School Student

17 year old Ashton Bonds died of disseminated MRSA infection

Prompts closing of school for cleaning

MRSA kills Football Player

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

An Epidemic A great deal of

media attention Public concern

MRSA and the Media

How Common is CA-MRSA colonization ?

General population analysis of data from the NHNES Colonized with Staph aureus 31.6%

84 million Colonized with MRSA 0.84%

2 million

Annals of Internal Medicine. 2006 March 7;144(5):318-25

How common is disease due to CA-MRSA?

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

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 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 1999Herold et al JAMA 1998:279:593-8Adcock et al JID 1998:178:577-80MMWR 1999;48:707-10

Community outbreaks

Native and aboriginal communities Sports teams Child care centers Military personnel Men who have sex with men Prison inmates and guards

Risk factors

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?

Importantly, many patients with CA-MRSA have no risk factors.

Is that all?

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

Resistance to Penicillin=B-lactamases

Resistance to Methicillin=Penicillin binding protein 2a (PBP 2a) Alterations in PBP 2a carried on

SCCmec Nosocomial MRSA=SCCmec II and III CA-MRSA=SCCmec IV

The USA300 strain

Necrotizing pneumonia caused by CA-MRSA

Outcomes in Patients Treated for CA-MRSA

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

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

Chlorhexidine washes Mupirocin or Bactroban ointment

applied to nares with a cotton-tipped applicator two to three times daily

Prevention of CA-MRSA

Handwashing Isolation Decolonization Vaccination??

Vaccine for Staph aureus

Capsular polysaccharides serotypes 5 and 8

Conjugated with protein from Pseudomonas exotoxin

Randomized trial in hemodialysis patients Partial immunity, decreased Staph aureus

bacteremias at 40 weeks By 54 weeks no difference ?booster doses

Passive immunization