In a Letter to the Editor of mBio, Professor Ron Fouchier published a calculation 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=1x10–7 per person per year, and since there are 10 workers with access to his laboratory, P1=1x10–6 per lab per year.
Compare this to P1=2x10–3 per lab per year for BSL3 laboratories calculated from CDC statistics for undetected or unreported LAIs, 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. [...],

Klotz, L. (2015). Comments on Fouchier's calculation of risk and elapsed time for escape of a laboratory-acquired infection from his laboratory. mBio, 6(2). doi:10.1128/mBio.00268-15