US anthrax cases linked

Americans have been told to be especially alert

Preliminary tests suggest that anthrax sent to a New York television station is the same strain as the bacteria which caused an outbreak in Florida.

The US Centre for Disease Control and Prevention (CDC) said that, following preliminary genetic testing, "the strain in New York appears to match the strain in Florida".

You've been exposed to anthrax. You're going to die

Letter sent to Senate Majority Leader Tom Daschle's office

News of the link came after the US House of Representatives, the Senate and House office buildings along with the Library of Congress in Washington were closed for tests after at least 31 congressional employees tested positive for anthrax exposure.

Two people are being treated for skin anthrax after a letter containing the bacteria was sent to NBC TV in New York, while the Florida outbreak - which centred on the offices of newspaper group American Media Inc - saw one man die and another need treatment for respiratory anthrax.

Officials said a matching strain did not necessarily mean the anthrax came from the same source, but the match may help investigators narrow in on the individuals or groups responsible.

US law enforcement officials have said there is no evidence linking the anthrax scares with foreign terrorists.

But with nerves on edge since the 11 September terror attacks on New York and Washington, the two threats are being increasingly linked.

White powder packages

The latest anthrax alert, which saw hundreds of Congressional workers in Washington queuing for tests, came after a letter containing anthrax spores was opened in the offices of Senate Majority Leader Tom Daschle.

Most of the people who tested positive for exposure to anthrax worked in the office. Five law enforcement personnel also tested positive.

Strains of anthrax

Respiratory: Similar beginnings to flu but shock occurs between two and six days later - frequently fatal

Intestinal: Severe food poisoning type symptoms - up to 50% mortality

Cutaneous: Rarely painful skin lesion - fatal in one in 20 cases

According to Senator John Kerry, the letter was opened by an assistant with a pair of scissors, at which point white powder leaked out.

A note inside warned: "You've been exposed to anthrax. You're going to die."

Senator Daschle stressed that the employees' positive nasal swabs only indicated exposure to anthrax, and that there was "absolutely no indication" that they had been infected.

He said they had all been taking antibiotics since last Friday. "It is treatable," he said.

Tests have determined that the anthrax found in the letter was professionally made but was not weapons-grade.

Investigators have found similarities in handwriting on envelopes containing anthrax

The US deputy surgeon-general, Ken Mortisugu, said the contamination was extremely limited and had not spread into the air-conditioning system.

While the Senate has decided to close all three of its office buildings, it still plans to convene on Thursday.

By contrast, the House of Representatives has suspended proceedings until next week. Speaker Dennis Hastert said the house would shut down to enable health officials to carry out tests in the Capitol complex, where more than 20,000 people work.

In New York, Governor George Pataki said there was "a likelihood" that there had been anthrax in his Manhattan offices.

He said tests taken on Monday night had produced positive results, but that three employees who were subsequently tested were not infected.

Mr Pataki said he and about 80 of his employees would be taking antibiotics as a precaution.

Mounting concern about the US cases has triggered alerts and hoaxes around the world, with the Israeli parliament evacuated along with public buildings in Europe, Africa and New Zealand.