A strain of MRSA that causes bloodstream infections is five times more lethal than other strains and has shown some resistance to the potent antibiotic drug vancomycin, says a new study by researchers at Henry Ford Hospital.
In the study, researchers 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.
The researchers said that the strain USA600 contains unique characteristics that may be linked to the high mortality rate.
However, they also said that 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.
"While many MRSA strains are associated with poor outcomes, the USA600 strain has shown to be more lethal and cause high mortality rates," said Carol Moore, 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," Moore added.
MRSA, or Methicillin-resistant Staphylococcus aureus, is a bacterium that is resistant to common antibiotics like enicillin. 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 nfections are often treated with vancomycin administered intravenously.
In this study, the USA600 strain was shown to be more resistant to vancomycin.
The study has been presented at the 47th annual meeting of the Infectious Diseases Society of America Oct 29-Nov.1 in Philadelphia.