Unraveling the dynamics of community-associated methicillin-resistant Staphylococcus aureus

Since the first description of the community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) strain USA300 [1] in the 1990s, this pathogen has emerged worldwide [2]. Within a decade, USA300 has become the most prevalent cause of community-acquired S. aureus infections in many settings in the United States [3]. Originally causing infections mainly in individuals without recent healthcare exposure, USA300 is increasingly causing hospital-acquired infections. There is, therefore, an urgent need for infection control measures. Although person-to-person transmission in the community must be the driving force of this epidemic [4], transmission dynamics and risk factors for colonization are still not well understood [5]. The study of Popovich et al in this issue of Clinical Infectious Diseases [6] is a next step in elucidating the dynamics of USA300. In their study they demonstrate that, compared to individuals not infected with human immunodeficiency virus (HIV), patients with HIV are more likely to be colonized with USA300 at hospital admission and that they are carrying USA300 at multiple body sites, such as the nares, throat, axillae, inguinal regions, and perirectal area, and in wounds, if present. Importantly, 38.5% of the USA300 carriers would have remained undetected if only nasal cultures had been obtained. This study emphasizes 2 important aspects in the transmission dynamics of USA300.