With this tool you can calculate the TCID50 of a virus stock with the Reed–Muench method (Reed and Muench 1938), the Spearman–Kärber method (Spearman 1908; Kärber 1931) and the improved Kärber method (Sun 1963), respectively.
Enter your data set on 'Initial/Dilution factor/Inoculating volume/ ' and numbers of 'Positive/Total'. Please note that it makes sense to have equal or decreasing values in the 'Observed (Positive)' column. And the values in the 'Observed (Total)' column must be identical. You can enter your own test set within 1-10.
First, the infection rate was calculated as:
Infection rate = number of cumulative positive units/(number of cumulative positive units + number of cumulative negative units).
With the dilutions that are closest to each other, above 50% positive and below 50% positive, the proportionate distance (PD) between these two dilutions is calculated in the following manner: PD=(positive above 50%−50%)/(positive above 50%−%positive below 50%).
We used a compound function to discriminate the dilutions spanning the ID50 laid and the remaining dilutions were shown as spaces. Then, logID50 = log(dilution with > 50% positive) + PD × (-log(dilution factor)).
When using the Spearman–Kärber method, the following formula can be used to directly estimate the 50% end point (Kärber 1931):
logID50=log(highest dilution giving 100% CPE)+0.5−(total number of test units showing CPE/number of test units per dilution).
Sun (1963) modified the Kärber method by incorporation of Bliss's weighting method (Bliss 1938) to calculate the median lethal doses of chemicals in animals. This method gives the 50% endpoint as:
logID50=log(dilution giving highest CPE)−log(dilution factor)× (∑infected rate at each dilution - 0.5).
This result is identical to that using the Spearman–Kärber method, but the improved Kärber method can also provide a 95% confidence interval (95% CI) for the logID50 by calculating its standard error (SE) as:
Then the 95% CI for logID50 is: logID50 ± 1.96×SE(logID50).
Chengfeng Lei, Jian Yang, Jia Hu, Xiulian Sun. On the Calculation of TCID50 for Quantitation of Virus Infectivity .VIROLOGICA SINICA, 2021, 36(1) : 141-144. http://dx.doi.org/10.1007/s12250-020-00230-5