President Barack Obama’s Democrats narrowly retained their Senate majority, losing at least six seats but beating tough challenges in key states like Nevada, West Virginia and California.

The anthrax strains surfacing with terrifying impact in Florida, New York and Washington are all similar, Bush administration said indicating a single source.

Thirty-one employees of the US Senate tested positive for exposure to a highly concentrated form of anthrax, officials said, prompting congressional leaders to order an unprecedented shutdown of some of their offices.