Jonathan Finkelstein is an established pediatric patient-oriented researcher, with extraordinary opportunities to mentor junior scientists in studies of critical issues in child health and health care. A Mid-career Investigator Award in Patient-oriented Research (K24) will allow dedicated time for Dr. Finkelstein to improve his mentoring capacities, and to provide additional opportunities for mentees related to care for common infections and antibiotic use in childhood. Dr. Finkelstein will leverage his current NIH-funded studies, access to extensive automated data through the HMO Research Network (HMORN), and resources of Harvard's CTSC program to understand the significant changes in treatment of infections in primary care practice, including patterns of antibiotic use, in an era when resistance has become commonplace, new vaccines may dramatically affect childhood illness, and parent and physician attitudes are in flux. This revised application proposes a more integrated and comprehensive approach to studying recent trends in care-seeking and treatment of common infections. It uses analysis of population-level data, as well as focus group and survey methods to understand underlying changes in parent knowledge, attitudes, and care-seeking. It also proposes a new focus on health care disparities in treatment of common infections aligning it with one of the primary goals of the T32-funded fellowship program in pediatric research which Dr. Finkelstein leads. The proposed mentoring plan includes 1) increased focus on mentoring research fellows in the Harvard-wide Pediatric Health Services Research Fellowship Program; 2) development of new opportunities for mentorship within Harvard's recently funded NIH Clinical and Translational Science Center; and, 3) ongoing engagement in the HMORN to develop innovative programs for cross-site mentorship of child health researchers. The past decade has witnessed a dramatic monotonic decrease in the use of antibiotics in pediatric practice driven by concerns about resistance by parents and clinicians. This has been associated with changes in diagnosis of otitis media, and other changes in health care utilization. Prior work has suggested differences, by social and demographic factors, in antibiotic use rates, as well as parental knowledge and attitudes regarding treatment. Since these studies, however, both the epidemiology and social context of childhood infections has changed dramatically. Infections with resistant non-vaccine serotypes of S. pneumoniae and methicillin resistant staph aureus have become increasingly common; new universal immunization for seasonal influenza is being implemented; and, the current H1N1 influenza pandemic is likely to impact parental views of, and care seeking for, respiratory tract illness. This research will address critical remaining questions including: how much longer the rate of antibiotic use continues to decrease; what its nadir will be among children in the US; whether previously observed differences, by socioeconomic and demographic factors, in knowledge, attitudes, and prescribing rates narrow or increase; and, whether patterns of care seeking and treatment for respiratory tract infections will change in the context of pandemic influenza. Finally, this work will address the effectiveness of public health messages in diverse populations regarding both common infections and pandemic influenza. These aims will be met using mixed methods that include analysis of claims data for the diverse populations of 4 participating health plans (including the addition of a plan predominantly serving Medicaid members), focus groups of parents to assess changing parental attitudes, and a quantitative survey to assess changes in knowledge related to infections and antibiotic (and antiviral) prescribing. In addition to supporting his own work, the data streams and analytic methods developed here will allow Dr. Finkelstein's trainees to conduct high quality patient oriented research on conditions affecting both the future of pediatric primary care practice and child health in the US.