CA-MRSA

2 May, 11

CA-MRSA
(Community Acquired Methicillin Resistant Staphylococcus aureus)

Facts

S. aureus is a common baciehum and is frequently present as a part of the normal human flora.
An estimated 25-30% of Hie population may be colonized; generally, the pathogen is harboured on the skin or in the nose without evidence of infection.
Earlier MRSA infections were more common in the nosocomial set-up only; however, recently, MRSAinfections not associated with hospitalization (CA-MRSA) are being reported worldwide.
The first report of CA-MRSA was published in the early 1990s in western Australia, while in the U.S., the lirstcasewas reported in 1982.
CMC Vellore. India (20O7) reports a CA-MRSA infection rate of 6.4% in patients with bloodstream and skin and soft tissue infection.
CA-MRSA is probably the most important challenge to routine practice in infectious disease management in internal and emergency medicine to have emerged over the last decade.
CA-MRSA strains are considered more virulent than hospital-acquired MRSA (HA-MRSA). leading toa significant problem in terms of morbidity and mortality if they reach the hospital population.
Genetic and microbiological studies have revealed that CA-MRSA is associated with a novel genetic and phenotypical profile.

MRSA Statistics

About 0.8% olthe U.S. population is colonized with MRSA.
Ta The proportion of HA-MRSA rapidly increased from 2% in ICUs in 1974 to 64% in 2004.
Approximately 1,26,000 hospitalizations yearly are due lo MRSA.
Recent data suggest that MRSA causes about 59% of all SSTIs.
Invasive (serious) MRSA infections occur in approximately 94,000 people each year and are associated with approximately 19,000 deaths reportedly more deaths than HIV per year.
Of the MRSA infections that cause death, about 86% are HA-MRSA and 14% are CA-MRSA.

Definition

According to the CDC, MRSA infection is considered to be community- acquired if the following factors are present:

Diagnosis is made in the outpatient setting or a positive culture result is obtained within 48 hours of hospitalization.
There is no history of MRSA infection or colonization.
There is no history in the past year of hospitalization; admission to a nursing home, skilled nursing facility, or hospice; dialysis; or surgery.
The patient has no permanent indwelling catheters or medical devices that pass through the skin into the body.

Pathogenicity of S. aureus is best characterized by its profound ability to evade the host's innate immune system. CA-MRSA strains have a substantially enhanced ability to do this by neutrophil lysis following phagocytosis at a more rapid rate as compared to HA-MRSAstrains.

CA-MRSA virulence is also enhanced by the production of various toxins, as given below:

1. Alpha-haemolysin (Hl_a): Demonstrates pore-forming activity towards a variety of host cells. Hla is a major virulence factor contributing to S. aureus pneumonia and is responsible for severe CA-MRSAinfections.
2. Panton-Valentine Leukocidin (PVL): Promotes lysis of human leucocytes by disrupting their outer membrane and can cause rapidly progressing haemorrhagic necrosis pneumonia.
3. Alpha-type phenol-soluble modulin (PSM_a) peptides: Responsible for the enhanced virulence factor of CA-MRSA strains as compared to HA-MRSA.
4. Delta-haemolysin.
5. Gamma-haemolysin.

Comparison of Clinical, Epidemiological and Microbiological Characteristics of HA-MRSA and CA-MRSA

Note: SCCmecA type IV accounts for the transformation of normal staphylococcal flora into MRSA

Clinical Manifestations

While CA-MRSA primarily causes skin and soft tissue infections, it can also cause serious invasive infections. Patients with skin infections may assume they have a spider bite because of the appearance of the initial lesion, which manifests as a red plaque, papule or indurate module that later spreads outwards.

Skin and Soft Tissue Infections
- Abscesses Cellulitis
- Furuncles/carbuncles
- Traumatic wound infections
Other Infections
- Necrotizing fascilitis
- Necrotizing pneumonia
- Sepsis/bacteraemia
- Sinusitis
- Urinary tract infections

Risk Factors for CA-MRSA Infection

Contact: Direct skin-to-skin contact, particularly that which is frequent or abrasive.
Crowded living conditions: Communal settings such as day care centres, jails, and shelters.
Compromised skin integrity: Abrasions, cuts, underlying dermatitis.
Contaminated surfaces and items: Objects and surfaces that may transmit infection.
Cleanliness: Lack of optimal personal hygiene, inadequate use of soap, inadequate cleaning practices.

Diagnosis

To differentiate between CA-MRSA and other aetiologies, query all patients about any history of MRSA infections, hospitalization or skilled nursing facility admission within the past one year and the risk factors as mentioned above.
Failure to respond to beta-lactam antibiotics, recurrent skin infections, and multiple people presenting skin infections at the same time may suggest a CA-MRSAinfection.
For localized SSTIs, a focused physical examination may be sufficient.
For more invasive disease, perform a complete physical examination, paying particular attention to signs of bacteraemia or systemic disease.
Laboratory evaluation should include culture and susceptibility testing.

While not routinely indicated, pulsed field gel electrophoresis and PCR amplification can demonstrate characteristic genetic differences and detect virulence and enterotoxin genes.

Recommended Treatment

Incision and drainage for localized skin infections.

Note:
I. Daptomycin gets deactivated by lung surfactant, hence is not recommended in lung infections. 6mg/kg q24h is recommended only in cSSTI concurrent with bacteremia.
ii. Clindamycin should not be used if the erythromycin-clindamycin D-zone test for resistance is positive.
iii. Minocyclin is not recommended for pregnant women or children <8 years old.
iv. Beta lactam antimicrobials can no longer be relied on as the sole empiric therapy for severely ill outpatients whose infection may be staphylococcal in origin.

Prevention

Good hand-hygiene practices.
Keeping open wounds, cuts and scrapes dry and covered, and not touching other people's cuts or bandages.
Not sharing personal items.
Patient education

At A Glance

D Test Procedure

According to NCCLS guidelines 2004 a disc containing erythromycin (15 ?g) is placed 15mm from centre to centre of a clindamycin (2 ?g) disc. Inducible resistance to clindamycin is manifested by flattening or blunting of the clindamycin zone of inhibition adjacent to the erythromycin disc, giving a D-shape to the zone of inhibited growth.

D-Zone test: D-shaped blunting of a circular zone of inhibition around Clindamycin (cd) disc on the side facing Erythromycin (E) disc.

Conclusion

S. aureus continues to be one of the most prominent human bacterial pathogens and the emergence of CA-MRSA further escalates the need for improved diagnostic, preventative and therapeutic modalities. Hence, prompt recognition of CA-MRSA infection, appropriate antibiotic use and institution of consistent prevention measures are essential.

References

1. Curr Opin Pharmacol 2009; 9:1 -7
2. http://www.aaos.org/news/aaosnow/may08/research1 .asp
3. http://www.cdc.gov/ncidod/dhqp/ar_mrsa_ca_clinicians.html accessed February 28,2006.
4. http://www.emedicinehealth.com/mrsa-infections Accessed on 18/09/09
5. http://www.narp.ca/pdf/education/CA-MRSA%202008%20NARP%20recommend.pdf
6.lnt J Antimicrob Agents 2009;34:S15-S19
7. J Hosp Infect 2007;67:109 -113 8Jaapa2006;19:4
9. Lancet 2002:359:753-759
10.4^th IDSA abstracts 2007;109
11. The Medical Letter 2006; 48:1228:13-15
12. Journal of Clinical and Diagnostic Research. 2009 ;(3)1513-1518

CA-MRSA

CA-MRSA(Community Acquired Methicillin Resistant Staphylococcus aureus)

D Test Procedure

CA-MRSA
(Community Acquired Methicillin Resistant Staphylococcus aureus)