U.S. intelligence analysts believed otherwise. Rumors of hundreds, even thousands of people killed in the 1979 outbreak continued to come in from Moscow, from emigrés in Western Europe, and from Soviet Jews newly settled in Israel, although no firsthand witnesses ever emerged. Calculations of the anthrax dose by some U.S. intelligence experts further inflamed the issue. A single gram of anthrax contains around a trillion potentially lethal spores. In a briefing on Sverdlovsk for President Jimmy Carter by Central Intelligence Director Stansfield Turner, the amount of anthrax released in the outbreak was estimated at seventy kilograms, an amount that could seriously infect tens of thousands of square miles. Matthew Meselson and U. S. government BW experts at the army's Dugway Proving Ground, who better understood the basic aerodynamics involved in such estimates, reckoned that as little as a gram of aerosolized anthrax, with its trillion spores, could have caused the Sverdlovsk outbreak. The figure settled on in Defense Intelligence Agency reports was ten kilograms.
The Soviet response to these suspicions was to adamantly stand by its tainted-meat explanation. In the spring of 1980 the U.S. government formed a working group on the Sverdlovsk outbreak, consisting of representatives from the Joint Chiefs of Staff, the National Security Council, the State Department, the CIA, and other agencies, to consider the incident. The group called on several outside experts: Philip Brachman from the Centers for Disease Control, Nobel Laureate microbiologist Joshua Lederberg at Rockefeller University in New York, Paul Doty, professor of biochemistry at Harvard, and Matthew Meselson. After some months, the majority judgment of the group was that an accidental explosion at the Sverdlovsk military factory caused an aerosol emission of virulent anthrax spores and that this emission resulted in many deaths from inhalation anthrax. The group also surmised that the emission caused an epizootic that brought infected meat to the black market. This inclusion of infected meat in the scenario (meat that could have been stored and eaten over a period of weeks) would account for the epidemic's reported long duration into early May, with people still falling ill and dying long after the initial explosion.