Time to revisit the endpoint dilution assay and to replace the TCID50 as a measure of a virus sample’s infection concentration
Fig 3
Comparing SIN to TCID50 and PFU for influenza A virus samples.
A,B: The infection concentration in two influenza A (H1N1) virus strain samples was measured via both an ED assay and a plaque assay (x, PFU). The ED assay was quantified in log10(TCID50) using the RM (square) or SK (triangle) methods, or in log10(SIN) using midSIN (circle with 68%,95% CI). Each of the 2 strain samples was measured over 2 separate experiments (Exp. #1, #2), performed each time by 2 different researchers (Researcher A or B), with 5 biological replicates each. The grey bars indicate the range of log10(SIN) values across the 5 replicates. The RM, SK, and SIN measures were estimated for each replicate based on the same ED plate. The experimental details are provided in Methods. C,D: The log10 of the ratio between either the TCID50 via the RM or SK method or the PFU, over the SIN via midSIN. The ratios were computed for each replicate (5 × 5 replicates), per experiment, per researcher (25 replicates × 2 researchers × 2 experiments = 100 ratios) shown as individual symbols (dots) for each method (RM, SK, PFU). The mean and 68% CI of the 100 ratios are indicated numerically and as black circles with error bars. The p-value indicates whether the ratios are statistically different from unity.