 Because it can be found in virtually all CA-MRSA strains that cause soft-tissue infections, it was long described as a key virulence factor, allowing the bacteria to target and kill specific white blood cells known as neutrophils.This view was challenged, however, when it was shown that removal of PVL from the two major epidemic CA-MRSA strains resulted in no loss of infectivity or destruction of neutrophils in a mouse model.Genetic analysis shows that PVL CA-MRSA has emerged several times, on different continents, rather than being the worldwide spread of a single clone.