  Recent H5N1 influenza research has revived the debate on the storage and
manipulation of potentially harmful pathogens. In the last two decades, new
high biosafety (BSL-4) laboratories entered into operation, raising strong
concerns from the public. The probability of an accidental release of a
pathogen from a BSL-4 laboratory is extremely low, but the corresponding risk
-- defined as the probability of occurrence multiplied by its impact -- could
be significant depending on the pathogen specificities and the population
potentially affected. A list of BSL-4 laboratories throughout the world, with
their location and date of first activity, was established from publicly
available sources. This database was used to estimate the total population
living within a daily commuting distance of BSL-4 laboratories, and to quantify
how this figure changed over time. We show that from 1990 to present, the
population living within the commuting belt of BSL-4 laboratories increased by
a factor of 4 to reach up to 1.8% of the world population, owing to an increase
in the number of facilities and their installation in cities. Europe is
currently hosting the largest population living in the direct vicinity of BSL-4
laboratories, while the recent building of new facilities in Asia suggests that
an important increase of the population living close to BSL-4 laboratories will
be observed in the next decades. We discuss the potential implications in term
of global risk, and call for better pathogen-specific quantitative assessment
of the risk of outbreaks resulting from the accidental release of potentially
pandemic pathogens
