"We were hampered by how much we could share on this quote-unquote secret initiative," she said.
After a week, it was clear that the BioWatch alarm was false.
In early 2004, on the eve of the Super Bowl in Houston, BioWatch once again signaled tularemia, desVignes-Kendrick said. The sample was from a location two blocks from Reliant Stadium, where the game was to be played Feb. 1.
DesVignes-Kendrick was skeptical but she and other officials again checked with hospitals before dismissing the warning as another false alarm. The football game was played without interruption.
Nonetheless, three weeks later, Charles E. McQueary, then Homeland Security's undersecretary for science and technology, told a House subcommittee that BioWatch was performing flawlessly.
"I am very pleased with the manner in which BioWatch has worked," he said. "We've had well over half a million samples that have been taken by those sensors. We have yet to have our first false alarm."
Asked in an interview about that statement, McQueary said his denial of any false alarm was based on his belief that the tularemia bacterium had been detected in Houston, albeit not from an attack.
"You can't tell the machine, 'I only want you to detect the one that comes from a terrorist,'" he said.
Whether the Houston alarms involved actual tularemia has never been determined, but researchers later reported the presence of benign relatives of the pathogen in the metropolitan area.
Fear in the capital
In late September 2005, nearly two years after the first cluster of false alarms in Houston, analysis of filters from BioWatch units on and near the National Mall in Washington indicated the presence of tularemia. Tens of thousands of people had visited the Mall that weekend for a book festival and a protest against the Iraq War. Anyone who had been infected would need antibiotics promptly.
For days, officials from the White House and Homeland Security and other federal agencies privately discussed whether to assume the signal was another false alarm and do nothing, or quarantine the Mall and urge those who had been there to get checked for tularemia.
As they waited for further tests, federal officials decided not to alert local healthcare providers to be on the lookout for symptoms, for fear of creating a panic. Homeland Security officials now say findings from lab analysis of the filters did not meet BioWatch standards for declaring an alert.
Six days after the first results, however, CDC scientists broke ranks and began alerting hospitals and clinics. That was little help to visitors who already had left town, however.
"There were 100 people on one conference call — scientists from all over, public health officials — trying to sort out what it meant," recalled Dr. Gregg Pane, director of Washington's health department at the time.
Discussing the incident soon thereafter, Jeffrey Stiefel, then chief BioWatch administrator for Homeland Security, said agency officials were keenly aware that false alarms could damage the system's credibility.
"If I tell a city that they've got a biological event, and it's not a biological event, you no longer trust that system, and the system is useless," Stiefel said on videotape at a biodefense seminar at the National Institutes of Health on Oct. 6, 2005. "It has to have a high reliability."
Ultimately, no one turned up sick with tularemia.
Culture of silence