Purpose: Recent data showing a high incidence of HIV infection among men who have sex with men (MSM) and other groups at high risk for acquiring HIV suggest that HIV screening more frequently than annually may be warranted. We assessed the cost-effectiveness of HIV screening for MSM, high risk heterosexuals (HRH) and injection drug users (IDUs) at 3 and 6 month intervals compared with annual screening.
Methods: We used a published mathematical model of HIV transmission to evaluate screening intervals for each population using cohorts of 10,000 MSM, HRH and IDU ages 14-64. We incorporated HIV transmissions averted due to serostatus awareness for each screening interval, as well as HIV testing costs and treatment costs saved from averted transmissions. Using surveillance and demographic data, we estimated HIV incidence to be 1.27% for MSM, 0.39% for IDU and 0.08% for HRH and conducted threshold analyses on incidence. We assumed conventional testing and 80% receipt of results.
Results: For MSM, HIV screening was cost-saving for both 6-month compared to annual screening, and quarterly compared to 6-month screening. Threshold values for HIV at which screening MSM was <$100,000 per QALY saved was 0.08% and 0.3% at the 6-month and quarterly screening intervals, respectively. Cost-effectiveness was below $100,000 per QALY saved for screening IDUs and greater than $100,000 per QALY saved for screening HRHs at 6-month intervals. For IDU and HRH the incidence threshold at which 6-month screening was <$100,000 per QALY saved was .12% for IDU and .10% for HRH.
Conclusion: HIV screening as frequently as quarterly for MSM and every 6-months for IDU populations is very cost-effective, while more frequent screening for HRH was greater than $100,000 per QALY saved. Reexamination of HIV screening intervals for MSM and IDU populations should be considered on the basis of the economic evidence. Table: Cost-effectiveness of HIV Screening at Different Intervals for MSM, IDU and HRH 
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