‘Tens of thousands of letters may contain anthrax'

Tens of thousands of letters mailed around the US could have picked up trace amounts of anthrax while passing through a contaminated postal centre, the nation’s top anthrax investigator has said.

Faced with mounting - yet circumstantial - evidence that a 94-year-old Connecticut woman died from cross-contamination in October, the question is of how big a problem the possibly contaminated mail poses.

‘‘There seems to be the potential for not just hundreds and not just thousands but tens of thousands letters to be at risk for some level of cross-contamination,’’ said Dr Jeffrey Koplan, director of the Centres for Disease Control and Prevention in Atlanta.

It has been almost eight weeks since the contamination at the Trenton, New Jersey, facility, however, and ‘‘with each passing day, the lack of further cases occurring is grounds to diminish the risk from any one of these letters,’’ Koplan stressed.

Investigators already have tracked 300 letters that passed through the Trenton facility within seconds of anthrax-laden letters mailed to two US senators.

Health officials in every area of the country that received the suspect letters are on alert. So far, Koplan said, no infections have turned up.

Two deaths during the anthrax bioterror attacks remain mysteries - 94-year-old Ottilie Lundgren, of Oxford, Connecticut; and 61-year-old Kathy Nguyen, of New York City.

Searches of their homes, mail and places the women frequented have found no signs of anthrax.

A trace of anthrax was found at a postal centre that processed mail for Lundgren’s hometown, and investigators discovered a letter containing a single anthrax spore at a home not far away.

That prompted Health and Human Services Secretary Tommy Thompson to declare Monday that he believes experts had enough evidence to label Lundgren’s death a case of cross-contamination from the mail.

‘‘I’m happy that we can tell the American people that part of the mystery’s been solved,’’ he told a reporter. ‘‘But at the same time I’m concerned about the cross-contamination, because you can’t see these little buggers, and where’s the next cross-contamination going to take place?’’

But yesterday, Thompson backtracked to say such evidence was circumstantial and that cross-contamination is ‘‘high on our list, but it’s not the only thing we’re looking at’’.

Homeland Security Director Tom Ridge echoed that, saying investigators have repeatedly tested Lundgren’s home and found no traces of anthrax.

Linking Nguyen to cross-contaminated mail is even harder: a letter addressed to a South Bronx business near her home went through the Trenton postal facility at about the same time as the anthrax-laden letters to Democratic Senators Tom Daschle and Patrick Leahy. The letter hasn’t been found.

Repeated anthrax studies suggest a mere trace amount - while able to cause the curable skin form of infection - is not enough to cause the deadly inhaled form of the disease, he said.

Still, scientists do not know the minimum safe level of anthrax and believe that people with weak immune systems could be infected by far lower amounts than it would take to sicken healthier people.

So CDC’s Koplan said people whose immune systems deficient might consider having other people open their mail or at least hold it away from the face.

Meanwhile in Washington, officials cleaning up the Senate office building where anthrax bacteria escaped on October 15 when the letter to Daschle was opened, hope the work will be completed in time to reopen the building early next year.

The Hart Senate Office Building was fumigated over the weekend.