Upper 95% Confidence Limit for Proportion of Specimens Containing Norovirus After Serial Negative Tests. Solid curve represents the upper 95% binomial confidence limit for test positivity (P(T+))using equation (1.0) in the text. Dashed lines represent upper 95% confidence limits for proportion of specimens truly positive for norovirus (P(NVG)). Solid horizontal line (at 55%) represents the approximate lower bound for proportion of positive specimens in documented outbreaks. PCR, real-time reverse-transcriptase polymerase-chain reaction; EIA, enzyme immunoassay; EM, electron microscopy; LCM, latent class model; CRS, composite reference standard.