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USA300 MRSA strain not more virulent than USA100 strain
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The USA300 strain of methicillin-resistant Staphylococcus aureus was associated with early complications in patients with community-onset pneumonia, recent data suggest. However, this strain did not appear to have an effect on mortality in patients with pneumonia or central-line–associated bloodstream infections when compared with the USA100 strain.
Among patients with pneumonia, factors associated with mortality included older age, being black or having the USA100 MRSA strain. Among patients with central line–associated bloodstream infections, factors associated with death included older age, comorbidities or being in the ICU prior to MRSA culture.
“USA300 does not appear to be more virulent than USA100 in hospitalized patients with central line-associated bloodstream infections or invasive pneumonia, as many health care providers and public health officials initially thought,” Fernanda Lessa, MD, MPH, of the division of health care quality promotion, National Center for Emerging and Zoonotic Infectious Diseases at the CDC, told Infectious Disease News. “Health care providers should continue to adhere to infection control practices regardless of the MRSA strain type that patients are infected with.”
Lessa and colleagues compared the differences in outcomes between infections caused by the two MRSA strains. The study included patients who had central line–associated bloodstream infections and patients with community-onset pneumonia from 2005 to 2007. The researchers reviewed medical records from patients with confirmed MRSA USA100 or USA300.
There were 236 patients with central line–associated bloodstream infections and 100 patients with community-onset pneumonia. Among patients with pneumonia, the USA300 strain was associated with early complications (OR=2.6). For patients with central line–associated bloodstream infections, ICU admission and Charlson comorbidity index were associated with late complications.
“It will be important to understand if similar findings are observed among patients with non-invasive or other types of invasive MRSA infection not included in our study,” Lessa said.
References:
Lessa FC. Clin Infect Dis. 2012;55:232-241.
Disclosures:
Dr. Lessa reports no relevant financial disclosures.