Molecular characterization of methicillin-susceptible Staphylococcus aureus clinical isolates in the United States, 2004 to 2010.

While much is known about the geographic distribution of different clonal types of methicillin-resistant Staphylococcus aureus (MRSA), few studies have assessed the molecular epidemiology of methicillin-susceptible S. aureus (MSSA), despite its continued clinical importance. In each U.S. Census region, reference laboratories collected successive MSSA isolates from patients with invasive or superficial staphylococcal infections for use in the Tigecycline Evaluation and Surveillance Trial. All isolates from the periods of 2004 to 2005 and 2009 to 2010 underwent antimicrobial susceptibility testing and characterization of their staphylococcal protein A (spa) type. Of the 708 isolates analyzed, 274 spa types were identified and divided into 15 genetic clusters. The most common clones were spa t002 (n = 63, 8.9%) and t008 (n = 56, 7.9%). While the distribution of the predominant spa types did not differ by U.S. Census region or time period, spa t008 was nearly twice as common in community skin and soft tissue infections than in nosocomial bloodstream infections (11.1% versus 5.6%, respectively; P = 0.008). Despite such differences, both community and nosocomial settings had diverse staphylococcal clonal types representing all major spa clusters. In contrast to those of MRSA, MSSA infectious isolates show wide genetic diversity without clear geographical or temporal clustering. Notably, the prevalent MSSA strains (spa t002 and spa t008) are analogous to the predominant MRSA clones, further demonstrating the importance of both lineages.

High prevalence of colonization with Staphylococcus aureus clone USA300 at multiple body sites among sexually transmitted disease clinic patients: an unrecognized reservoir.

Extranasal colonization is increasingly recognized as an important reservoir for Staphylococcus aureus among high-risk populations. We conducted a cross-sectional study of multiple body site colonization among 173 randomly selected STD clinic patients in Baltimore, Maryland. Staphylococcal carriage at extranasal sites, including the oropharynx, groin, rectum, and genitals, was common among study subjects. The USA300 clone was particularly associated with multiple sites of colonization compared with non-USA300 strains (p = .01). Given their high burden of multi-site colonization and confluence of established staphylococcal risk factors, STD clinic patients may represent a community-based reservoir for S. aureus and be well suited for innovative infection control initiatives.

Staphylococcus aureus oropharyngeal carriage in a prison population.

Throat carriage (42.7%) of Staphylococcus aureus exceeded nasal carriage (35.0%) in 2 New York prisons. Methicillin resistance, primarily due to USA300, was high at both sites; 25% of dually colonized inmates had different strains. Strategies to reduce S. aureus transmission will need to consider the high frequency of throat colonization.