New epidemiology of Staphylococcus aureus infections.

More than a century after its description, Staphylococcus aureus is still a dangerous pathogen for humans. Despite constant improvement in patient care, S. aureus infections remain associated with considerable morbidity and mortality, both in hospitals and in the community [1]. The clinical and molecular epidemiology of S. aureus infections has changed dramatically over the past two decades, with the emergence of community-associated methicillin-resistant S. aureus (CA-MRSA). These changes have been quickly identified, thanks to the unusual combination in CA-MRSA of methicillin resistance and low rates of resistance to non-b-lactam antimicrobials. Interestingly, these clones have emerged and spread in patients who lack the classic epidemiological risk factors for methicillin-resistant S. aureus (MRSA) infection, such as healthcare contact, suggesting that CA-MRSA epidemics could originate from unexpected areas and populations. This worrying observation has highlighted the renewed importance of epidemiological surveys of S. aureus infections and of the molecular characterization of S. aureus strains. Such surveillance has been extensively conducted in North America and Europe, leading to the identification of novel CA-MRSA clones and, more recently, of livestock-associated MRSA [2]. However, North America and Europe account for less than one-third of the world’s population, and little is known about the epidemiology of S. aureus outside of these areas. Because of the increasing population movements worldwide, there is an urgent need to improve our understanding of S. aureus epidemiology in non-western parts of the world. In an attempt to bridge this information gap, this Special Issue aimed to collect and review the available epidemiological data in Africa, Asia, the Middle East and Oceania, to sketch an integrated view of S. aureus carriage and infection dynamics in terms of prevalence, antimicrobial resistance, and molecular characteristics. With respect to the African continent, the paper by Schaumburg et al. [3] identified several distinctive traits of S. aureus epidemiology, both in developed urban populations and in remote rural communities. By far the most striking feature of this epidemiology is the very high prevalence, ranging from 17% to 74%, of the genes encoding the potent leukotoxin Panton–Valentine leukocidin (PVL) in S. aureus isolates. Most of these PVL-positive isolates are methicillin-susceptible, which makes PVL epidemiology in Africa different from that in both Europe, where the prevalence of PVL-positive S. aureus is <2%, and North America, where the prevalence is very high but is mostly attributable to the exceptional diffusion of a single CA-MRSA clone. The high prevalence of PVL-positive S. aureus in sub-Saharan Africa, the antimicrobial multisusceptibility of the corresponding strains and the genetic diversity of the PVL-positive lineages strongly suggest that this geographical area could act as a reservoir for the emergence of PVL-positive clones. Moreover, the now-established PVL endemicity in Africa largely explains why PVL-related infections have been frequently described in western patients travelling to the continent.