MRSA bloodstream infection linked to high mortality rate

A strain of MRSA that causes bloodstream infections is five times more lethal than other strains and has shown to have some resistance to the potent antibiotic drug vancomycin used to treat MRSA, according to a Henry Ford Hospital study.

The study found that 50 percent of the patients infected with the strain died within 30 days compared to 11 percent of patients infected with other MRSA strains.

The average 30-day mortality rate for MRSA bloodstream infections ranges from 10 percent to 30 percent.

Researchers say the strain USA600 contains unique characteristics that may be linked to the high mortality rate. But they say it is unclear whether other factors like the patients' older age, diseases or the spread of infection contributed to the poor outcomes collectively or with other factors. The average age of patients with the USA600 strain was 64; the average age of patients with other MRSA strains was 52.

The study is being presented at the 47th annual meeting of the Infectious Diseases Society of America Oct. 29-Nov.1 in Philadelphia.

"While many MRSA strains are associated with poor outcomes, the USA600 strain has shown to be more lethal and cause high mortality rates," says Carol Moore, PharmD., a research investigator in Henry Ford's Division of Infectious Diseases and lead author of the study.

"In light of the potential for the spread of this virulent and resistant strain and its associated mortality, it is essential that more effort be directed to better understanding this strain to develop measures for managing it."

MRSA, or Methicillin-resistant Staphylococcus aureus, is a bacterium that is resistant to common antibiotics like penicillin. It can cause skin, bloodstream and surgical wound infections and pneumonia. The majority of infections occur among patients in hospitals or other health care settings, though a growing number of infections are being acquired by otherwise healthy people outside those settings.

MRSA strains can be resistant to many drugs, though they are typically susceptible to the antibiotic vancomycin. MRSA infections are often treated with vancomycin administered intravenously. The USA600 strain in this study was shown to be more resistant to vancomycin.