MRSA dropping in hospitals; elsewhere, not so much

Apr 24, 2013 (CIDRAP News) – The latest data from the US Centers for Disease Control and Prevention (CDC) suggest that hospitals have cut their incidence of invasive methicillin-resistant Staphylococcus aureus (MRSA) infections in half since 2005, but the decline in community-associated MRSA infections has been far more modest.

At a conference this week, CDC officials reported that the incidence of invasive MRSA infections in hospitals dropped an estimated 54% between 2005 and 2011, while the incidence of community-associated infections declined only 5% during that time.

The latest numbers show the continuation of a trend that was first noted about 5 years ago, said Raymund Dantes, MD, MPH, an Epidemic Intelligence Service (EIS) officer with the CDC's Division of Healthcare Quality Promotion. He presented the findings this week at the CDC's 62nd Annual EIS Conference in Atlanta.

The data come from the CDC's Active Bacterial Core Surveillance (ABCs) program, part of the Emerging Infections Program Network, which covers about 19.4 million people in nine metropolitan areas around the country.

In the program, invasive MRSA cases are classified as hospital-onset (HO) if they are identified more than 3 days after hospital admission. A second category is "healthcare-associated community-onset" (HACO), which means they occurred in an outpatient or early in a hospital stay in a patient who has a risk factor such as hospitalization, surgery, or dialysis within the past year. Infections that don't fit in either of these two categories are considered community-associated (CA).

Investigators used data from the ABCs to develop national estimates of MRSA incidence, employing information from the US census and US Renal Data System, according to the study abstract.

Dantes and colleagues estimated the national total of MRSA infections in 2011 at 80,461, a decrease of 30,800 from the estimated 111,261 cases in 2005, according to his poster presentation. The estimated rate in 2011 was 25.82 cases per 100,000 population, down from 37.54 per 100,000 in 2005, a 31% decrease.

The estimated rate of HO cases dropped from 9.91 per 100,000 in 2005 to 4.54 in 2011, or 54%, Dantes reported. Over the same period, the estimated rate of HACO infections declined about 28%—from 21.46 to 15.52 per 100,000.

But the estimated incidence of CA cases decreased only 5%, or from 5.59 to 5.21 per 100,000, according to the report.

"Between 2009 and 2011 there was a small but noticeable drop in the community-associated rate, but it went back up in 2011," Dantes told CIDRAP News. "We expect some variation from year to year, but we aren't seeing a large change from 2005 to 2011."

He said the sustained drop in healthcare-related MRSA infections is not surprising, commenting, "We started seeing those declines in a publication released in 2008."

The ABCs program doesn't assess factors contributing to changes in MRSA incidence, but the past few years have brought high awareness and a host of national and facility-level initiatives to reduce healthcare-associated infections, Dantes said. "We hope that this is a result of efforts on all levels," he added.

"Though we see an impressive decline in healthcare-associated infections, to bring the rate down further we need to look at cases that have onset in the community now," Dantes said.

The CDC is not yet ready to suggest specifically how to bring down the rate of community-associated MRSA infections, he said. "We still need to learn a little about how that's happening."

European MRSA findings
In other recent MRSA-related findings, European researchers reported that about 22% of a large sample of patients from primary care networks in nine European countries were colonized with S aureus, but less than 2% of the isolates were MRSA. Their report was published in the May issue of The Lancet Infectious Diseases.

An international team obtained nasal swabs from 32,206 healthy patients from family physician networks in Austria, Belgium, Croatia, France, Hungary, Spain, Sweden, the Netherlands, and the United Kingdom. S aureus was isolated from 21.6% of the patients, with the prevalence in adults ranging from 12.1% in Hungary to 29.4% in Sweden.

The investigators found 91 isolates that were MRSA, amounting to 1.3% of the 6,956 S aureus isolates. Belgium had the highest MRSA prevalence at 2.1%, while Sweden had none. The team also found a wide variety of genotypes among the MRSA isolates.

Another finding was that azithromycin was the drug to which S aureus strains were most often resistant, with prevalence ranging from 1.6% in Sweden to 16.9% in France.

See also:

Abstract of CDC MRSA study, covering results only for 2005 to 2010

CDC ABCs report on MRSA for 2011

Lancet Infect Dis abstract of European study

Related Lancet Infect Dis editorial (excerpt)

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