To: Jill who wrote (295 ) 11/3/2001 9:55:30 AM From: RocketMan Read Replies (1) | Respond to Here is data to support the suggestion that the NY death may have come from a very low number of spores (as little as nine). At levels that low, I doubt if we would find much evidence of other spores around her.... the US Army standardized a value of 8,000 inhaled anthrax spores as the dosage lethal for 50 percent of a human population receiving it, the so-called LD50. But nowhere in Sverdlovsk was the fatality rate 50 percent. Even at the ceramics factory pipe shop, apparently right on the centerline of the passing spore cloud, only ten of about 450 workers fell ill and died, a fatality rate of 2 percent. To estimate the dosage that would infect 2 percent of an exposed monkey (or human) population, one must extrapolate downward from data obtained from experiments with much higher dosages. Different mathematical models have been developed for doing this. The "log-normal" model used for years by US Army BW scientists to calculate anthrax munitions requirements and risk factors sensibly assumes that the exposed population is heterogeneous, that is, that some people are more susceptible to infection than others. In Sverdlovsk, for instance, adults certainly seemed more susceptible than children and teenagers; and it is not hard to believe that some adults were more resistant than others. Using the army's specific log-normal model for anthrax, one easily obtains the astonishing result that while the inhalation of 8000 spores is required to infect half of an exposed population, a mere mine spores per individual would infect 2 percent of the population. Could a dosage on only nine spores have infected ten of the 450 pipe shop workers? No one can say for sure.
