Experts from the CDC (Centers for Disease Control and Prevention) report that MRSA infections have dropped significantly in the USA over the last four years. Researchers examined data from 2005 through to the end of 2008 of nine American metropolitan areas. They reveal that health care-associated invasive methicillin-resistant Staphylococcus aureus (MRSA) infections fell among patients with infections that began in the community or in the hospital>

You can read about this in more detail in an article in JAMA (Journal of the American Medical Association).

It is estimated that 1.7 million health care associated infections are closely linked to about 99,000 deaths in US hospitals every year.

MRSA stands for methicillin-resistant Staphylococcus aureus. The term is used to describe a number of strains of the bacteria, Staphylococcus aureus, that are resistant to a number of antibiotics, including methicillin. Staphylococcus aureus is a group of bacteria that live on the surface of people’s skin and inside the nose. It is normally harmless: most people who are carrying it are totally unaware that they have it. In fact, it is thought that up to 30% of the general UK population carries these bacteria in their nose or on their skin. This group of bacteria can be spread quite easily from person to person through contact.

Problems occur if Staphyloccocus aureus bacteria are able to enter the body through a cut or wound.

Most healthy people have strong immune systems and are able to fight off a Staphylococcus aureus infection themselves and have only mild symptoms. However, people with weakened immune systems (for example due to other illnesses) or who have undergone sugery (for example heart surgery or hip replacement) can develop more serious problems. In more vulnerable people, Staphyloccocus aureus bacteria have been known to cause boils, abscesses, impetigo, septic wounds, heart-valve problems and toxic shock syndrome. In extreme cases, it can result in death.

People with weakened immune systems who have been infected with Staphylococcus aureus require treatment with antibiotics to help clear the infection. The concern with MRSA strains of bacteria is that they are resistant to a number of the antibiotics that are normally used to treat Staphylococcus aureus infections.

Alexander J. Kallen, M.D., M.P.H., of the Centers for Disease Control and Prevention (CDC), Atlanta, and team used a population-based surveillance system to assess the occurrence of invasive health care-associated MRSA infections from 2005 through 2008 in nine metropolitan areas covering a population of approximately 15 million individuals.

All reports of laboratory-identified episodes of invasive (from a normally sterile body site, i.e., such as the bloodstream) MRSA infections were assessed and classified based on the setting of the positive culture and the presence or absence of health care exposures.

Eighty-two per cent of the total infections, which were included in the analysis, came from health care-associated infections, such as hospital-onset and health care-associated community-onset.

The evaluation revealed that there were:

  • 21,503 cases of invasive MRSA infections for the years 2005 through 2008
  • 17,508 cases either hospital-onset or health care-associated community-onset.
  • Most health care-associated infections (15,458 [88 percent]) involved a positive blood culture and were classified as a bloodstream infection (BSI).

The authors wrote:

The modeled incidence, adjusted for age and race, of hospital-onset invasive MRSA infections significantly decreased 9.4 percent per year from 2005 through 2008; while there was a significant 5.7 percent decrease per year in the modeled incidence of health care-associated community-onset infections. This would equate to about a 28 percent decrease in all hospital-onset invasive MRSA infections and about a 17 percent decrease in all invasive health care-associated community-onset infections over the 4-year period.

An analysis of just blood stream infections revealed a larger decrease in the modeled yearly incidence rates of both hospital-onset (-11.2 percent) and health care-associated community-onset (-6.6 percent) BSIs, equating to about a 34 percent decrease in all hospital-onset MRSA BSIs and about a 20 percent decrease in all health care-associated community-onset BSIs over the 4-year period.

The researchers say they do not know why the observed decrease in invasive health care-associated MRSA infection incidence occurred. Perhaps the dissemination of MRSA prevention practices in many U.S. hospitals played a role.

The authors wrote:

..this evaluation demonstrates that the incidence of hospital-onset and health care-associated community-onset invasive MRSA infections has decreased dramatically and significantly in this large geographically diverse population. Taken together with data from more than 600 intensive care units nationwide, these findings suggest that there is a real decrease in MRSA infection rates among patients in U.S. hospitals. As highlighted in the recently finalized U.S. Department of Health and Human Services Action Plan to Prevent Healthcare-Associated Infections, prevention of invasive MRSA infections is a national priority.

Although these data suggest progress has occurred in preventing health care-associated MRSA infections, more challenges remain. Increasing adherence to existing recommendations and addressing MRSA transmission and prevention beyond inpatient settings are challenges that will require further effort and investigation if eliminating the goal of preventable health care-associated invasive MRSA infections is to be attained.

“Health Care-Associated Invasive MRSA Infections, 2005-2008”
Alexander J. Kallen, MD, MPH; Yi Mu, PhD; Sandra Bulens, MPH; Arthur Reingold, MD; Susan Petit, MPH; Ken Gershman, MD, MPH; Susan M. Ray, MD; Lee H. Harrison, MD; Ruth Lynfield, MD; Ghinwa Dumyati, MD; John M. Townes, MD; William Schaffner, MD; Priti R. Patel, MD, MPH; Scott K. Fridkin, MD; for the Active Bacterial Core surveillance (ABCs) MRSA Investigators of the Emerging Infections Program
JAMA. 2010;304(6):641-647. doi:10.1001/jama.2010.1115

Written by Christian Nordqvist