One of the strategies commonly used to mitigate healthcare associated infections (HAIs) and decrease pathogen colonization burden relies on topical antiseptic agents, including chlorhexidine gluconate (CHG). While there is clear benefit from the use of these agents, concern exists for the potential for microbial adaptation, as is the case with virtually every antibiotic. A number of genes encoding multidrug efflux pumps in Staphylococcus aureus, including qacA/B and smr, have been associated with elevated MICs to antiseptics with such organisms often termed antiseptic tolerant S. aureus (ATSA). A study of S. aureus infections in pediatric oncology patients revealed an increase in ATSA following an escalation in CHG use. Among S. aureus infections, the presence of antiseptic tolerance (AT) genes is independently associated with nosocomial acquisition of infection and underlying medical conditions. Importantly, ATSA are also associated with resistance to systemic antimicrobials and invasive infection. These data support the concept of the healthcare environment selecting for organisms with reduced susceptibility to antiseptics, which in turn are associated with a severe disease phenotype. AT genes have likewise been reported in other important HAI pathogens including coagulase-negative staphylococci (CoNS). Notably, there are few longitudinal studies which assess the impact of repeated healthcare or antiseptic exposure on colonization with these organisms. Furthermore, the exact impact of AT genes on the efficacy of antiseptics is controversial given the very high concentrations used in practice. Thus, a better understanding of these unintended consequences of infection prevention measures and their clinical relevance is necessary and within the mission of AHRQ and the FOA. Our long-term goal is to develop a greater understanding of the factors promoting antiseptic/antibiotic resistant infections. We hypothesize that the healthcare environment and medical complexity predispose to the acquisition of antiseptic tolerant organisms (ATOs) in children. We propose a prospective cohort study to longitudinally examine colonization with ATOs. Children with a new diagnosis of malignancy (high-risk cohort) as well as healthy children (low-risk cohort) will be enrolled; both groups will have nasal and axillary cultures obtained at three-month intervals over one year. Specific Aim 1 will assess the rate of colonization with ATSA in the high-risk cohort compared to the low-risk cohort with a goal of determining the point at which risk for acquisition increases in the high-risk cohort. Specific Aim 2 will explore the disease causing potential of ATSA by examining incident infection rates in enrolled subjects with respect to ATSA colonization status, as well as through microbial genomic studies. Specific Aim 3 will examine the impact of AT genes on survival of S. aureus following exposure to clinically relevant antiseptic solutions in a catheter disinfection assay. In Specific Aim 4, the impact of healthcare exposure on colonization with antiseptic tolerant-CoNS will be assessed. This work will provide important data to guide infection prevention measures; as this study evaluates the potential consequences of the current standard of care, the results will be translatable directly into practice.