Most of the following information is from Dr. Jaime Carrizosa's presentation at the January 26, 2008, MRSA Symposium.
S. aureus & MRSA:
Although there has been recent media attention about MRSA, MRSA infections are not new. MRSA is a common bacteria that has been around for a long time that has become increasingly virulant as it acquired resistance genes.
S. aureus resistance:
The percent of S. aureus resistant to antiobiotics in ICUs has increased from 37% in 1995 to 60% in 2004. An increased resistance is being seen worldwide.
Where S. aureus is found:
- 2/3 to 3/4 of humans are colonized by S. aureus at some point
- 20% to 50% are colonized at any given time
- 0% - 20% are persistently colonized
- The anterior nares is the most common site of colonization
- 80% to 90% of strains causing diseases come from endogenous flora
S. aureus is the most common cause of:
- Endocarditis (38%)
- Nosocomial infection (13%)
- Skin and soft tissue infections (20%)
- Cellulitis, osteomyelitis, septic arthritis
- Bacteremia, nosocomial pneumonia, food-borne disease, implant infection, abscess, etc
Breakdown of S. aureus infections:
- Methicillin sensitive Staph aureus (MSSA)
- Methicillin resistant Staph aureus (MRSA); which includes:
- Hospital Acquired MRSA (HA-MRSA)
- Community-Acquired MRSA (CA-MRSA)
Percentage of all infections that are S.aureus:
- MSSA 2% - 10%
- MRSA 5% - 30%
Community-Acquired MRSA (CA-MRSA)
CA-MRSA usually presents as a skin & soft tissue infection (SSI). Many patients will come in for a "spider bite", but the only spider bite that causes a SSI is the brown recluse spider, and bites from the brown recluse are exceedingly rare in Florida. "Spider bites" should be considered CA-MRSA until proven otherwise!
A study of the prevalence of CA-MRSA in 2004 showed that in 11 Emergency Departments throughout US, in 422 patients with skin & soft tissue infection:
- 320/422 (75%) were caused by S. aureus
- MRSA accounted for 59% (15% - 74%)
- USA300 strain made up 97%
Why CA-MRSA is different:
In CA-MRSA, the Staph casette chromosone (SCC) mec IV is mobile and is seen in a variety of background strains
CA-MRSA replicates more rapidly than HA-MRSA (23 min vs 46 min), so CA-MRSA is considered a “more fit” bacteria than HA-MRSA.
Analysis of CA-MRSA has shown 19 putative virulence genes: 4 Enterotoxins, 11 exotoxins (such as Panton-Valentine Leukocidin, or PVL), collagen adhesin, etc., which may make CA-MRSA more virulent
The LD of CA-MRSA is 5x less than HA-MRSA (no single gene appears responsible)
Why PVL (Panton-Valentine Leukocidin) is important:
- PVL was first described in 1932
- PVL is a bicomponent synergistic membrane-tropic toxin
- PVL is encoded by lukS-PV and lukF-PV genes
- PVL is assembled as hetero-oligimers that synergistically act to form pores in cell membranes (lysis) of pmns and monocytes/macrophages
- PVL is associated with necrotizing skin and soft tissue infections and pneumonia
The distinction between CA-MRSA and HA-MRSA is blurring!
In a study that characterized 132 cases of MRSA BSI in Atlanta:
- 34% of MRSA were USA 300
- 28% of pts with HA BSI factors
- 20% of pts with nosocomial BSI
Who usually gets infected with MRSA:
- Infectious Disease physicians
- Family members of those who have been previously diagnosed
- Hospital personnel, especially Nurse Practitioners
- Residents of extended care facilities
- Patients hospitalized for other medical reasons
Treatment of CA-MRSA:
- 75% - 80% of cases of CA-MRSA present with skin & soft tissue infections
- Many cases can be treated with I&D only - without antibiotics
- 73% of patients in one study received antibiotics to which the organisms were resistant. There was no difference in number of follow-up visits, subsequent need for I&D, or change in antibiotic therapy (Fridkin, NEJM, 2005)
Adult oral antibiotic treatment options:
- TMP/SMX DS - 1 to 2 BID for 7-10 days
- Minocycline or Doxycycline 100mg BID for 7-10 days
- Clindamycin 300-450mg BID for 7-10 days (resistance developing)
Pediatric oral antibiotic treatment options:
- TMP 8-12mg + SMX 40-60mg/kg/day in 2 doses for 7-10 days
- Clindomycin 10-20mg/kg/day in 3-4 doses for 7-10 days (resistance forming)
Treatment of recurrent CA-MRSA furunculosis:
- There is little data indicating long-term benefit of decolonization regimens. Potential toxicity of agents, their cost, and the potential for creating resistance need to be considered.
Options for treatment include:
- A combination of topical, mucosal, and systemic antibiotics, such as oral TMP-SMX, nasal mupirocin (Bactroban), chlorhexidine showers (Hibiclens) 5 times a day
- Bleach baths (1 teaspoon of bleach per gallon of water) x 10 minutes 2 times/wk
- Environmental cleaning (bedclothes, towels, surfaces)
- More controversial is the consideration of treating close contacts
- There may be some potential transmission from pets, so pet reservoirs need to be considered for recurrent cases
- Environmental transmissions may also need to be considered in some cases
MRSA – FAQs:
Do we need to use special techniques when culturing for MRSA?
- No. S. aureus is easy to culture using standard culture tubes
- The best place to culture for carriers is the anterior nares
- Rapid screening tests for MRSA are available and should be considered if there is an urgency to make a diagnosis (see Xpert MRSA distributed by Cepheid)
How can we protect our patients and ourselves from MRSA?
The main MRSA precaution is hand washing compliance
Studies indicate that healthcare professionals follow routine hand washing recommendations 16 to 85% of the time, with most studies showing rates less than 50%
What about using "gimmicks" to increase handwashing compliance?
- Studies done to date have not shown that any specific "gimmick" increases hand washing compliance
- Having the primary hospital administrator openly committed to promoting handwashing has been the most effective mechanism to increase hand washing compliance
What about routine surveillance cultures for MRSA?
- There have been numerous reports of improved control of MRSA (primarily in short-term outbreak settings) through application of contact isolation and surveillance cultures, such as the experience reported in Netherlands and Northern Europe Strategies to Reduce Transmission of Antimicrobial Resistant Bacteria in the ICU (STAR-ICU)
- However, recently Huskins, et al., in SHEA 2007, published a prospective, cluster-randomized study of using standard hand washing precautions vs. several intense control strategies (ICS)
- The study included 5434 patients in ICS ICUs vs 3705 pts in standard ICUs
- The result was that there was NO differences in the patient populations as to co-morbidity, severity of illness, length of stay, devices used or antibiotics needed
- Subsequently, at this time, routine surveillance cultures of all patient for MRSA has not been recommended
Should high risk employees & physicians be screened for MRSA?
- Routine screening of employees and physicians is not recommended at this time. Individuals who are MRSA carriers cannot be discriminated against or be denied employment unless there is documented recurrent transmission of MRSA infections from that individual.
Is MRSA a reportable disease?
- Invasive MRSA infections in hospitals (i.e., positive blood cultures) are reportable. Routine positive cultures from skin and soft tissues is not.
What is the best anti-bacterial soap for MRSA?
- Hibiclens is available over-the-counter.
Is Purell effective against MRSA?
- All alcohol gels and foams like Purell are very effective against MRSA.
Should Bactroban be used to prevent MRSA colonization?
- The routine use of Bactroban in the nares has not been shown to prevent colonization.
Should family members of MRSA patients use Hibiclens washes?
- Family members of patients who are MRSA carriers should scrub weekly with Hibiclens. They should scrub more often if skin eruptions are present.
Have other counties instituted comprehensive MRSA control plans?
- Not to our knowledge at this time.
What is the role of aminoglycosides in treating HA-MRSA?
Gentamicin (in combination with a B-lactam antibiotic or Vancomycin) results in more rapid killing and clearance of blood cultures and defervescence of fever. Goal is peak level of 3-5 ug/mL, 3-5 days. This may be associated with renal toxicity (particularly in elderly).
What is the role of Rifampin?
Rifampin (in combination with a B-lactam antibiotic or Vancomycin) can result in indifference, antagonism, or synergism. Rifampin in combination with fluoroquinolones yields synergism.
What agents are on the horizon to treat MRSA?
- Oxazolidinones: Linezolid (Zyvox)
- Quinupristin/Dalfopristin (Synercid)
- Daptomycin (Cubicin)
- Tigecycline (Tygacil)
What are some of the investigational anti-Staphylococcal antibiotics?
- Ortivancin (InterMune)
- Telavancin (Theravance)
- DFHA Inhibitors
- Iclaprim (Arpida)
- Novel B-lactams
How should MRSA patients be handled in the emergency department?
When it isn't possible to place patients in separate rooms, the principles of contact precautions (hand hygiene, gloves and gowns for contact, proper disinfection of the area after the patient is discharged) should still be applied in areas only separated by curtains.*
What precautions are needed when transporting a MRSA patient?
A chief concern is avoiding actions that require any attendant to touch the patient and then possibly contaminate environmental surfaces (door handles, elevator buttons, etc). If a single caretaker is transporting a patient, gown and gloves should be worn until the patient is on the stretcher or wheelchair, and then gloves should be removed and hands washed.
If a patient might require hands-on intervention during transport, the safest approach is to have two individuals transport the patient. One should wear gown and gloves and is responsible for touching the patient, while the other (without gloves) handles the doors and elevator buttons.*
What is the best way to manage a MRSA patient on a behavioral unit?
Most behavioral units are low-risk settings for the transmission of MRSA, so these units are treated like community settings and are considered exempt from hospital isolation guidelines (other than if a patient has an actively draining wound infected or colonized by MRSA). The best way to prevent MRSA transmission on a unit would be to educate patients and staff to practice good hand hygiene. Patients should not share potentially contaminated personal items such as towels, soap or razors.*
What about room cleaning once a MRSA patient is discharged?
Routine cleaning procedures should be followed for floors and walls. Surfaces visably soiled should be washed first before disinfecting. Frequently touched surfaces (bedrails, bathroom fixtures, etc) need special attention. Curtains should be cleaned when visably soiled. Most EPA-registered hospital disinfectants should adequately inactivate MRSA.*
How long does MRSA remain viable in the environment?
Days to weeks.
* From "Questions About MRSA and Answers From the Experts" by Laura Stokowshi, RN, MS; http//www.medscape.com/viewarticle/546221