Number needed to test (NNT) to detect one active HCV infection Number needed to test (on a logarithmic scale) to detect one active HCV infection, in different scenarios for targeted HCV-testing. The two intervals at the top are based prevalence estimates for the Swiss general population, assuming that 75% of those ever infected develop chronic infection, and each reflecting the respective lower and upper limit. The remaining eleven point estimates with 95% confidence intervals represent MSM recruited at Checkpoint Zurich, reflecting the whole sample (n = 840; thus including 19 men with diagnosed HIV) or sub-samples based on individual characteristics. (1) Estimate based on blood donors and pregnant women ; (2) Estimate based on mathematical modelling ; (3) High anti-HCV prevalence (>3.5%) countries were defined according to Modh Hanafiah et al. 2012 ; (4) Non-injection drug use (NIDU) of cocaine/amphetamines; (5) Any of the following: NIDU of cocaine/amphetamines, being tattooed, being pierced, receptive fisting, group sex (proxy measure), or a history of lesion-prone STIs (proxy measure); (6-7) Birth cohort screening (1955-1974/1955-1984) as discussed as add-on strategies by Bruggmann et al. 2013.