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

In a Letter to the Editor of mBio, Professor Ron Fouchier published a calculation (1) in which he finds a very low probability, P1, for a laboratory-acquired infection (LAI) for a single lab for a single year. Claiming numerous safety precautions in his biosafety level 3 (BSL3 ) laboratory, Fouchier calculates P1 1 10–7 per person per year, and since there are 10 workers with access to his laboratory, P1 1 10– 6 per lab per year. Compare this to P1 2 10–3 per lab per year for BSL3 laboratories calculated from CDC statistics for undetected or unreported LAIs (2, 3), here called “community LAIs,” as it is assumed that an undetected or unreported LAI represents an infection that has traveled outside the lab and into the community. Recently reported escapes of LAIs from high-level biocontainment at CDC laboratories (4) and the long history of LAIs and other escapes from laboratories (5) also argue that Fouchier’s value for P1 is too low. Lipsitch and Inglesby (6) have supplied additional arguments as to why the Fouchier value for P1 is likely much too low. Fouchier uses a simplistic formula, y 1/P1, to calculate the elapsed time in years for an LAI to escape from his laboratory, y 1/(1 10– 6) 1 106, 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 likelihood consequences, starting with the P1 probability, specifically: potential pandemic fatalities (probability of a community LAI) (probability that the community LAI leads to a pandemic) (estimated fatalities in a pandemic). My risk calculation estimates the likelihood of a community LAI for both a single laboratory and n laboratories conducting this research over y years. The total number of laboratories involved in this potential pandemic pathogen research is called here the “research enterprise.” A single, easily derived equation is used to determine the likelihood of a community LAI: