THE CONTROL AND PREVENTION OF METICILLIN RESISTANT STAPHYLOCOCCUS AUREUS

The Control and Prevention of Meticillin Resistant Staphylococcus Aureus (MRSA) in Health Care Facility

   By Medhat A.Lamfon, PhD

Methicillin-resistant Staphylococcus aureus (MRSA) is a bacterium responsible for several difficult-to-treat infections in humans. It may also be called multidrug-resistant Staphylococcus aureus or oxacillin-resistant Staphylococcus aureus (ORSA).

MRSA is, by definition, any strain of Staphylococcus aureus bacteria that has developed resistance to beta-lactam antibiotics which include the penicillins (methicillin, dicloxacillin, nafcillin, oxacillin, etc.) and the cephalosporins.

MRSA is especially troublesome in hospitals where patients with open wounds, invasive devices and weakened immune systems are at greater risk of infection than the general public.

Signs and Symptoms

Staphylococcus Aureus most commonly colonizes the anterior nares (the nostrils), although the respiratory tract, opened wounds, intravenous catheters, and urinary tract are also potential sites for infection. Healthy individuals may carry MRSA asymptomatically for periods ranging from a few weeks to many years. Patients with compromised immune systems are at a significantly greater risk of symptomatic secondary infection.

MRSA can be detected by swabbing most of the nostrils of patients and isolating the bacteria found inside. Combined with extra sanitary measures for those in contact with infected patients, screening patients admitted to hospitals has been found to be effective in minimizing the spread of MRSA in hospitals in the United States[1], Denmark, Finland, and the Netherlands.[2]

MRSA may progress substantially within 24–48 hours of initial topical symptoms. After 72 hours, MRSA can take hold in human tissues and eventually become resistant to treatment. The initial presentation of MRSA is small red bumps that resemble pimples, spider bites, or boils that may be accompanied by fever and occasionally rashes. Within a few days the bumps become larger, more painful, and eventually open into deep, pus-filled boils.[3] About 75 percent of community-associated (CA-) MRSA infections are localized to skin and soft tissue and usually can be treated effectively. However, some CA-MRSA strains display enhanced virulence, spreading more rapidly and causing illness much more severe than traditional healthcare-associated (HA-) MRSA infections, and they can affect vital organs and lead to widespread infection (sepsis), toxic shock syndrome and necrotizing ("flesh-eating") pneumonia. This is thought to be due to toxins carried by CA-MRSA strains, such as PVL and PSM, though PVL was recently found to not be a factor in a study by the National Institute of Allergy and Infectious Diseases (NIAID) at the NIH. It is not known why some healthy people develop CA-MRSA skin infections that are treatable whereas others infected with the same strain develop severe infections or die.[4]

The most common manifestations of CA-MRSA are skin infections such as necrotizing fasciitis or pyomyositis (most commonly found in the tropics), necrotizing pneumonia, infective endocarditis (which affects the valves of the heart), or bone or joint infections.[5] CA-MRSA often results in abscess formation that requires incision and drainage. Before the spread of MRSA into the community, abscesses were not considered contagious because it was assumed that infection required violation of skin integrity and the introduction of staphylococci from normal skin colonization. However, newly emerging CA-MRSA is transmissible (similar, but with very important differences) from Hospital-Associated MRSA. CA-MRSA is less likely than other forms of MRSA to cause cellulitis.

Risk Factors

At risk populations include:

Hospital Patients

Many MRSA infections occur in hospitals and healthcare facilities, with a higher incidence rate in nursing homes or long-term care facilities. Rates of MRSA infection are also increased in hospitalized patients who are treated with quinolones. Healthcare provider-to-patient transfer is common, especially when healthcare providers move from patient to patient without performing necessary hand-washing techniques between patients.[6][10]

Prison Inmates

In confined environments such as prisons, with continual admission of new members who may typically be in poor health and adopt poor hygiene practices, there have been a number of challenges reported first in the U.S. and then in Canada. The earliest reports were made by the CDC in state prisons. Subsequently reports of a massive rise in skin and soft tissue infections were reported by the CDC in the Los Angeles County Jail system in 2001, and this has continued. Pan et al. reported on the changing epidemiology of MRSA skin infection in the San Francisco County Jail, noting the MRSA accounted for >70% of S. aureus infection in the jail by 2002. Lowy and colleagues reported on frequent MRSA skin infections in New York State Prisons. Two reports on inmates in Maryland have demonstrated frequent colonization with MRSA.

In the news media hundreds of reports of MRSA outbreaks in prisons appeared between 2000 and 2008. For example, in February 2008, The Tulsa County Jail in the U.S. State of Oklahoma started treating an average of twelve Staphylococcus cases per month.[11] A report on skin and soft tissue infections in the Cook County Jail in Chicago in 2004-5 demonstrated that MRSA was the most common cause of these infections among cultured lesions and furthermore that few risk factors were more strongly associated with MRSA infections than infections caused by methicillin-susceptible S. aureus. In response to these and many other reports on MRSA infections among incarcerated and recently incarcerated persons, the Federal Bureau of Prisons has released guidelines for the management and control of the infections although few studies provide an evidence base for these guidelines.

People in contact with live food-producing animals

Cases of MRSA have increased in livestock animals. CC398 is a new clone of MRSA that has emerged in animals and is found in intensively reared production animals (primarily pigs, but also cattle and poultry), where it can be transmitted to humans. Although being dangerous to humans CC398 is often asymptomatic in food-producing animals.[12]

Athletes

In the United States, there have been increasing numbers of reports of outbreaks of MRSA colonization and infection through skin contact in locker rooms and gyms, even among healthy populations. A study published in the New England Journal of Medicine[13] linked MRSA to the abrasions caused by artificial turf. Three studies by the Texas State Department of Health found that the infection rate among football players was 16 times the national average. In October 2006, a high school football player was temporarily paralyzed from MRSA-infected turf burns. His infection returned in January 2007 and required three surgeries to remove infected tissue, as well as three weeks of hospital stay.[14] MRSA has also been found in the public school systems throughout the country.[15]

Children

MRSA is also becoming a problem in pediatric settings,[16] including hospital nurseries.[17] A 2007 study found that 4.6% of patients in U.S. health care facilities were infected or colonized with MRSA.[18]

Diagnosis

Diagnostic microbiology laboratories and reference laboratories are key for identifying outbreaks of MRSA. New rapid techniques for the identification and characterization of MRSA have been developed. This notwithstanding, the bacterium generally must be cultured via blood, urine, sputum, or other body fluid cultures, and grown up in the lab in sufficient numbers to perform these confirmatory tests first, so there is no quick and easy method to diagnose an MRSA infection, therefore initial treatment is often based upon 'strong suspicion' by the treating physician, since any delay in treating this type of infection can have fatal consequences. These techniques include Real-time PCR and Quantitative PCR and are increasingly being employed in clinical laboratories for the rapid detection and identification of MRSA strains.[19][20]

Another common laboratory test is a rapid latex agglutination test that detects the PBP2a protein. PBP2a is a variant penicillin-binding protein that imparts the ability of S. aureus to be resistant to oxacillin.[21]

Strains

In the UK, where MRSA is commonly called "Golden Staph", the most common strains of MRSA are EMRSA15 and EMRSA16.[22] EMRSA16 is the best described epidemiologically: it originated in Kettering, England, and the full genomic sequence of this strain has been published.[23] EMRSA16 has been found to be identical to the ST36:USA200 strain, which circulates in the United States, and to carry the SCCmec type II, enterotoxin A and toxic shock syndrome toxin 1 genes.[24] Under the new international typing system, this strain is now called MRSA252. It is not entirely certain why this strain has become so successful, whereas previous strains have failed to persist. One explanation is the characteristic pattern of antibiotic susceptibility. Both the EMRSA15 and EMRSA16 strains are resistant to erythromycin and ciprofloxacin. It is known that Staphylococcus aureus can survive intracellularly,[25], for example in the nasal mucosa [26] and in the tonsil tissue ,[27]. Erythromycin and Ciprofloxacin are precisely the antibiotics that best penetrate intracellularly; it may be that these strains of S. aureus are therefore able to exploit an intracellular niche.

Community-acquired MRSA (CA-MRSA) is more easily treated, though more virulent, than hospital-acquired MRSA (HA-MRSA). CA-MRSA apparently did not evolve de novo in the community but represents a hybrid between MRSA that spread from the hospital environment and strains that were once easily treatable in the community. Most of the hybrid strains also acquired a factor that increases their virulence, resulting in the development of deep-tissue infections from minor scrapes and cuts, as well as many cases of fatal pneumonia.[28]

In the United States, most cases of CA-MRSA are caused by a CC8 strain designated ST8:USA300, which carries SCCmec type IV, Panton-Valentine leukocidin, PSM-alpha and enterotoxins Q and K,[24] and ST1:USA400.[29] Other community-acquired strains of MRSA are ST8:USA500 and ST59:USA1000. In many nations of the world, MRSA strains with different predominant genetic background types have come to predominate among CA-MRSA strains; USA300 easily tops the list in the U. S. and is becoming more common in Canada after its first appearance there in 2004. For example, in Australia ST93 strains are common, while in continental Europe ST80 strains predominate (Tristan et al., Emerging Infectious Diseases, 2006). In Taiwan, ST59 strains, some of which are resistant to many non-beta-lactam antibiotics, have arisen as common causes of skin and soft tissue infections in the community. In a remote region of Alaska, unlike most of the continental U. S., USA300 was found rarely in a study of MRSA strains from outbreaks in 1996 and 2000 as well as in surveillance from 2004-6 (David et al., Emerg Infect Dis 2008).


Prevention

Screening Programs

Patient screening upon hospital admission, with nasal cultures, prevents the cohabitation of MRSA carriers with non-carriers, and exposure to infected surfaces. The test used (whether a rapid molecular method or traditional culture) is not as important as the implementation of active screening.[30] In the United States and Canada, the Centers for Disease Control and Prevention issued guidelines on October 19, 2006, citing the need for additional research, but declined to recommend such screening.[31][32]

In some UK hospitals screening for MRSA is performed in every patient [33] and all NHS surgical patients, except for minor surgeries, are previous checked for MRSA.[34] There is no community screening in the UK however screening of individuals is offered by some private companies [35]

In a US cohort of 1300 healthy children, 2.4% carried MRSA in their nose.[36]

Surface sanitizing

Alcohol has been proven to be an effective surface sanitizer against MRSA. Quaternary ammonium can be used in conjunction with alcohol to extend the longevity of the sanitizing action.[37] The prevention of nosocomial infections involves routine and terminal cleaning. Non-flammable Alcohol Vapor in Carbon Dioxide systems (NAV-CO2) do not corrode metals or plastics used in medical environments and do not contribute to antibacterial resistance.

In healthcare environments, MRSA can survive on surfaces and fabrics, including privacy curtains or garments worn by care providers. Complete surface sanitation is necessary to eliminate MRSA in areas where patients are recovering from invasive procedures. Testing patients for MRSA upon admission, isolating MRSA-positive patients, decolonization of MRSA-positive patients, and terminal cleaning of patients' rooms and all other clinical areas they occupy is the current best practice protocol for nosocomial MRSA.

 

References

 

  1. Study at the Veterans Affairs hospital in Pittsburgh: "Science Daily" ([dead link]). http://www.sciencedaily.com/upi/index.php?feed=Science&article=UPI-1-20070727-15235200-bc-us-infections.xml. 
  2. McCaughey B. "Unnecessary Deaths: The Human and Financial Costs of Hospital Infections" (PDF). Archived from the original on July 11, 2007. http://web.archive.org/web/20070711030535/http://www.tufts.edu/med/apua/Patients/ridbooklet.pdf. Retrieved 2007-08-05. 
  3. "Symptoms". Mayo Clinic. http://www.mayoclinic.com/health/mrsa/DS00735/DSECTION=symptoms. 
  4. "MRSA Toxin Acquitted: Study Clears Suspected Key to Severe Bacterial Illness". NIH news release. National Institute of Health. 2006-11-06. http://www3.niaid.nih.gov/news/newsreleases/2006/staphtoxin.htm. 
  5. Raygada JL and Levine DP (March 30, 2009). "Managing CA-MRSA Infections: Current and Emerging Options". Infections in Medicine 26 (2). http://www.consultantlive.com/infection/article/1145625/1393856. 

 

Tacconelli, E.; De Angelis, G.; Cataldo, MA.; Pozzi, E.; Cauda, R. (Jan 2008). "Does antibiotic exposure increase the risk of methicillin-resistant Staphylococcus aureus (MRSA) isolation? A systematic review and meta-analysis.". J Antimicrob Chemother 61 (1): 26–38. doi:10.1093/jac/dkm416