ts based on the Medicare reimbursement schedule. We assumed that 100% of screened Results HIV and HCV Infections Averted With no purchase NVP-BHG712 screening targeted to individuals in ORT, we estimate that 7371 HIV infections and 25,704 HCV infections will occur over the next 20 years in a population of 2.5 million with 26,100 IDUs entering ORT. Screening only for chronic HIV infection averted 13.8 to 27.6 HIV infections and, primarily through riskreducing behavior changes associated with awareness of HIVpositive status, a very small number of HCV infections. Screening only for chronic HCV infection averted 18.0 to 20.0 HCV infections and 2.3 to 2.5 HIV infections. HIV infections were averted by HCV screening because all individuals newly diagnosed with one infection were screened for the other during follow-up; due to its relatively high prevalence and low rate of awareness, HCV screening results in a large absolute number of diagnoses and, therefore, HIV tests. Screening for HIV antibodies with increased frequency averted few incremental infections. For example, increasing screening frequency from annually to twice-annually averted only 3.3 additional HIV infections over 20 years. Incorporating HIV RNA testing to identify acute infections averted many more infections than increasing the frequency of HIV screening: PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/22212565 for screening frequency of upon entry to ORT to every 3 months, including RNA detection averted 14.8 to 30.3 more HIV infections, respectively, than antibody screening alone. Across all screening strategies considered, approximately 52% of infections averted were averted in the non-IDU population. Identifying 1 IDU in ORT with chronic HIV with a CD4 count,500 cells/ mm3 and initiating ART 
averted 0.1 HIV infections over 20 years. Diagnosis during the acute phase averted more HIV infections than later diagnosis even if ART is not initiated: over 20 years, diagnosing 1 IDU in ORT with acute HIV infection averted 0.4 HIV infections if ART was not immediately initiated and 1.3 HIV infections if ART was immediately initiated. Compared to screening for HCV antibodies annually, screening twice annually averted no additional HCV infections over 20 years. Including HCV viral RNA detection averted an additional 3.7 to 7.7 infections over 20 years compared to antibody screening alone for screening frequency of upon entry to ORT to every 3 months, respectively. Early identification and treatment of HCV averts few infections primarily because not all acutely infected individuals will progress to chronic infection and HCV re-infection is common, absent behavior change. Cost Effectiveness of HIV and HCV Screening HIV and HCV Prevalence Screening of IDUs in ORT for HIV and HCV prevents infections but has little effect on overall HIV and HCV prevalence because the number of people targeted through screening in ORT is small. Compared to no screening, the relative change in HIV prevalence in the total population in year 20 is 0.20% and 0.23% lower with annual and twice-annual HIV antibody testing, respectively; whereas the relative change in HIV prevalence in year 20 is 0.43% and 0.51% lower with annual and twice-annual HIV antibody and RNA testing, respectively. In the IDU population, twice-annual screening for HIV antibody and RNA decreases HIV prevalence in year 20 by 1.1% compared to no screening. Across all strategies considered, the relative change in HCV prevalence in the total population in year 20 was Cost Effectiveness of HIV and HCV Screening reduced
