Dominant Strain of Drug-Resistant MRSA Decreases in Hospitals but Persists in the Community

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This scanning electron micrograph (SEM) depicted numerous clumps of methicillin-resistant Staphylococcus aureus bacteria, commonly referred to by the acronym, MRSA; Magnified 2381x. Recently recognized outbreaks, or clusters of MRSA in community settings have been associated with strains that have some unique microbiologic and genetic properties, compared with the traditional hospital-based MRSA strains, which suggests some biologic properties, e.g., virulence factors like toxins, may allow the community strains to spread more easily, or cause more skin disease. A common strain named USA300-0114 has caused many such outbreaks in the United States. Image courtesy of the CDC

The incidence of the most common strain of methicillin-resistant Staphylococcus aureus (MRSA) infections has decreased in hospital-onset cases, but has failed to decline in the broader community, according to new research published online today in the journal Infection Control & Hospital Epidemiology.

The USA 300 strain of MRSA, has become prevalent in both communities and healthcare institutions. "In looking at risk factors for hospital or community-onset USA 300, current or former drug use was a strong predictor for acquiring this strain of bacteria," according to Kyle J. Popovich, MD, MS, the lead author of the study and Assistant Professor in the Section of Infectious Diseases, Rush University Medical Center, Chicago.

In the past 15 years, MRSA infections have evolved as the bacterium emerged as a significant pathogen in the community and hospitals in the U.S. Researchers studied 1,015 cases of Staphylococcus aureus bacterial bloodstream infections over a six-year period at a Chicago "safety net" hospital. The study found that more than half of hospital-acquired cases were due to the USA 300 strain.

Recent national surveillance has suggested a decrease in the incidence of invasive hospital-acquired MRSA infections during the past decade, and researchers said their findings reaffirmed that observation in the Chicago region.

"Decreases in hospital-onset MRSA BSIs may be due to substantial efforts aimed to reduce healthcare-associated infection," says Popovich. "Enhanced prevention efforts in the community for certain populations, such as those engaging in illicit drug use, may be necessary to further curb the spread of invasive MRSA infections."

Reference: Yoona Rhee, Alla Aroutcheva, Bala Hota, Robert A. Weinstein, Kyle J. Popovich. "Evolving Epidemiology of Staphylococcus aureus Bacteremia." Web (Sept. 16, 2015).

Source: Society for Healthcare Epidemiology of America

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