Comments on Fouchier’s Calculation of Risk and Elapsed Time for Escape of a Laboratory-Acquired Infection from His Laboratory

Klotz, Lynn C.

Fouchier uses a simplistic formula, y Ï­ 1/P 1 , to calculate the elapsed time in years for an LAI to escape from his laboratory, y Ï­ 1/(1 Ï« 10 -6 ) Ï­ 1 Ï« 10 6 , that is, the million years stated in his Letter. It is not clear what this calculation tells us. Does it give us the elapsed time for a 10% chance that an LAI occurs? Does it give us elapsed time for a 50% chance, or an 80% chance? In this regard, the elapsed time for a 100% chance is infinite, as we can never be absolutely certain that an LAI will occur. I suggest attaching little weight to this elapsed time calculation and instead concentrating on risk Ï­ likelihood Ï« consequences, starting with the P 1 probability, specifically: potential pandemic fatalities Ï­ (probability of a community LAI) Ï« (probability that the community LAI leads to a pandemic) Ï« (estimated fatalities in a pandemic).