Using the 23% prevalence from Stucker et al10 gives estimated probabilities of infection of 86% following a positive CRP test result and 5.6% following a negative test result. The Box provides details of the calculations, which use likelihood ratios11 estimated using the data from Liu et al. 8 Both post-test probabilities are somewhat lower than those found in the setting described by Liu et al,8 which is a reflection of the reduced prevalence of infection in the Swiss population. Here, CRP is linked to infection.