Reply to “Studies on Influenza Virus Transmission between Ferrets: the Public Health Risks Revisited”

Lipsitch, Marc; Inglesby, Thomas V.

Fouchier proposes another measure of accident rate, the number of accidents per worker-year, where a worker is defined as a person with access approval to a BSL2, -3, or -4 lab that handles select agents. From these data he calculates a rather low risk of Ͻ1 per 70,000 worker-years, using the Henkel et al. (6) denominator, including all agents at all biosafety levels, and the numerator of known viral infections. This suffers from the same conceptual and statistical problems noted above and from the additional problem that the individuals "approved" to have access to a select agent facility will be highly heterogeneous in the amount of time they actually spend there. A more relevant metric, we suggest, is that estimated for the intramural labs in NIAID, which experienced 3 known LAIs in 634,500 person-hours of actually work in a BSL3 lab, or about a 1% risk for every 2,000 h of work in a BSL3 lab (8) .