Table 1.
Calculation of ID50 for MHV68 intranasal inoculation of 129S1/SVImJ miceb
| Virus dilution (PFU) | No. of infected test units (mice)a | Cumulative infected (A) | Cumulative uninfected (B) | Ratio of A/(A + B) | % infected |
|---|---|---|---|---|---|
| 100 | 10/10 | 17 | 0 | 17/17 | 100.00 |
| 10 | 6/10 | 7 | 4 | 7/11 | 63.64 |
| 1 | 1/10 | 1 | 13 | 1/14 | 7.14 |
a
Infection was determined by plaque assay of the lungs harvested at 8 days after inoculation.
b
Proportionate distance = [(% positive above 50%) − 50%]/[(% positive above 50%) − (% positive below 50%)]; proportionate distance = (63.64 − 50)/(63.64 − 7.14) = 0.24. Log ID50 = (log dilution above 50%) + (proportionate distance × log dilution factor) = 1 + (0.24 × −1) = 0.76; ID50 = 100.76 = 5.75 PFU.