ess of screening IDUs for acute/early HCV infection; that study found antibody screening every 6 months and initiation of treatment to be highly cost effective and potentially cost-saving. However, that study assumed that 100% of identified cases among IDUs would be eligible for PEG-IFN+RBV treatment and did not include the possibility of re-infection, which is known to occur. Our analysis has several limitations. Our `representative city’ does not perfectly represent the HIV-HCV co-epidemic in IDUs in any purchase SB 743921 specific U.S. city. However, via sensitivity analysis of key `city-specific’ parameters we attempted to demonstrate the fairly wide generalizability of our model findings and to show how results change for cities with very high rates of ORT use or relatively low rates of HIV in IDUs. We only capture new infections among adults aged 15 to 59. Including older individuals would minimally impact the results as few new infections occur in persons over age 60. We did not include benefits from maternal transmissions averted or from contact tracing. Inclusion of these benefits may increase the cost effectiveness of screening. We did not consider screening for other diseases that also occur frequently in this population such as hepatitis B virus infection. We did not consider HIV screening technologies including rapid or oral tests, or the recently approved at-home HIV test. We did not include the risks of poor ART adherence resulting in drug-resistant HIV and the increase in costs associated with treating drug-resistant infections. We did not include many of the 
potential effects on behavioreither positive or negativethat might accrue from very frequent screening and counseling such as increased condom use or increases in serosorting. Finally, we estimated the lifetime costs, LY, and QALYs for all individuals in the model at the end of the intervention horizon based on their terminal health state using a model in which we did not continue the screening intervention and did not allow for any additional disease transmission. Although these two assumptions may have resulted in overestimations of the LYs and QALYs gained in this period, these estimates had little influence on the cost effectiveness of strategies. Currently, testing for acute HIV is not widely available outside of pilot programs, and access to HIV and HCV counseling, testing, and treatment varies widely across drug treatment programs. Fewer than 50% of IDUs receive the recommended annual testing for HIV and HCV. For acute HIV screening to be effective, testing of samples, reporting of results, and initiation of treatment must occur quickly. Infrastructure changes and education of substance abuse workers and associated health professionals may be required. Our analysis indicates that not testing IDUs in ORT frequently for acute and chronic HIV infection is a missed public health opportunity. Such screening could reduce the number of new HIV infections and would be cost effective. Supporting Information analysis. Sensitivity analysis on HIV parameters. Incremental cost-effectiveness ratio for selected strategies on the efficient frontier compared to the next-best strategy. Acknowledgments The authors thank Steven Hurd for his assistance with computing resources. The multimeric and multi-domain protein von Willebrand factor is essential to mediate adhesion of platelets to the site of vascular PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/22211890 injury under high shear stress conditions like in arteries and arterioles. The A1, A2 and A3