A quantitative assessment of Staphylococcus aureus community carriage in Yuma, Arizona

Abstract

Staphylococcus aureus is a frequent cause of mild and severe infections that occur when these commensal bacteria penetrate the outer layers of skin or mucosa. As most S. aureus infections are the result of autoinfection, and community-acquired infections are increasingly common, it is important to better understand S. aureus colonization characteristics in the community setting. Using standard culture technique and a quantitative PCR assay (SaQuant), we detected and quantified S. aureus across the nares, throat, and palm of 548 community-dwelling individuals in southwestern Arizona. Using culture-based methods, we detected S. aureus colonization in the nares of 26.3% of individuals (n = 144); however, the combination of two detection methods across multiple body sites resulted in much higher prevalence than has been reported previously. Overall, 65.9% of participants were colonized, with significantly higher prevalence in males (compared to females) and non-Hispanics (compared to Hispanics), with this pattern especially evident in nares and throat samples. Colonizing quantities in the nares were slightly higher in males and significantly greater among non-Hispanics. The clear sex and ethnicity patterns warrant further investigation in order to identify and leverage protective factors that may drive these disparities. In the nares, S. aureus density was the highest, most variable, and correlates with colonization in other body sites such as throat and palm. Our results demonstrate that screening by culture-based methods only can miss individuals colonized by S. aureus and that previous carriage statistics are likely underestimates. By including a highly sensitive quantitative assay, this work provides a roadmap towards more comprehensive and accurate characterization of S. aureus carriage and the potential for more effective mitigation.AUTHOR SUMMARYEffective disease control and prevention is tied to pathogen identification and understanding reservoirs. Staphylococcus aureus infection prevention efforts and protocols are based upon decades of research on colonization patterns and associated links to subsequent infection. Unfortunately, efforts to prevent S. aureus infections have been met with diminishing returns, suggesting significant gaps in fundamental knowledge of colonization. However, this knowledge and resulting protocols, are founded upon culture-based detection. By employing a new quantitative PCR assay on samples from three body sites in 548 individuals, we can characterize colonization more comprehensively than previous studies by describing both prevalence and pathogen quantity. Our highly sensitive detection resulted in an overall prevalence of 65.9%. Higher quantities were associated with the nares and were highest among non-Hispanic males (86.9%). Overall prevalence was much higher than has been previously documented. Common research practices, such as culture-based detection from a single body site, may misclassify over half of colonized persons. Future studies incorporating quantitative data, especially with longitudinal sampling at more body sites will provide a more wholistic understanding of community carriage, colonization dynamics, and likelihood of autoinfection and transmission.