Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections are caused primarily by a single strain—USA300—of an evolving bacterium that has spread with “extraordinary transmissibility” throughout the United States during the past five years, according to a new study led by National Institutes of Health (NIH) scientists. CA-MRSA, an emerging public health concern, typically causes readily treatable soft-tissue infections such as boils, but also can lead to life-threatening conditions that are difficult to treat. The study, from the National Institute of Allergy and Infectious Diseases (NIAID) of NIH, resolves debate about the molecular evolution of CA-MRSA in the United States. The findings rule out the previously held possibility that multiple strains of USA300, the most troublesome type of CA-MRSA in the United States, emerged randomly with similar characteristics. The study also offers a hypothesis for the origin of previous S. aureus outbreaks, such as those caused by penicillin-resistant strains in the 1950s and 1960s.
