A 94-year-old woman stricken with inhalation anthrax has died in hospital, bringing the total of anthrax deaths in the US to five.
Investigators are baffled as to how the woman, whose name has not been revealed, came in contact with the deadly spores.
Most of the 17 cases of inhalation anthrax or the less deadly skin anthrax confirmed by the Centre for Disease Control since the scare broke out have involved people with ties to the US Postal Service, the US government or media figures. Meanwhile, a senior scientist has stated the anthrax attacks in America almost certainly derived from a US government laboratory.
Barbara Rosenberg, chairman of the Federation of American Scientist's group on biological weapons said the spores probably derived from a defence lab.
She says the anthrax attacks demonstrate the incredible potency of using disease as a weapon.
"My city has been attacked, first by foreign terrorists, then by an American using a weaponised biological agent."
Rosenberg was representing one of a number of arms-control groups that urged a 144 nation conference in Geneva to tighten restrictions on germ warfare in the 1972 Biological Weapons Convention.
The anthrax used in letters sent to addresses in New York City, Florida and Washington, "was derived, almost certainly, from a US defence laboratory," said Rosenberg.
"But was only a small taste of what is possible." Five people have now died as a result of the toxin, including the 94-year-old woman who died this afternoon.
PA/AFP