Dr. Jonathan Fielding, Los Angeles County's public health director, whose department has presided over several BioWatch false positives, referred questions to Homeland Security officials.
Dr. Takashi Wada, health officer for Pasadena from 2003 to 2010, was guarded in discussing the BioWatch false positive that occurred on his watch. Wada confirmed that the detection was made, in February 2007, but would not say where in the 23-square-mile city.
"We've been told not to discuss it," he said in an interview.
Dr. Karen Relucio, medical director for the San Mateo County Health Department, acknowledged there was a false positive there in 2008, but declined to elaborate. "I'm not sure it's OK for me to talk about that," said Relucio, who referred further questions to officials in Washington.
In Arizona, officials kept quiet when BioWatch air samplers detected the anthrax pathogen at Super Bowl XLII in February 2008.
Nothing had turned up when technicians checked the enclosed University of Phoenix Stadium before kickoff. But airborne material collected during the first half of the game tested positive for anthrax, said Lt. Col. Jack W. Beasley Jr., chief of the Arizona National Guard's weapons of mass destruction unit.
The Guard rushed some of the genetic material to the state's central BioWatch lab in Phoenix for further testing. Federal and state officials convened a 2 a.m. conference call, only to be told that it was another false alarm.
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Although it never made the news, the incident "caused quite a stir," Beasley said.
The director of the state lab, Victor Waddell, said he had been instructed by Homeland Security officials not to discuss the test results. "That's considered national security," he said.
The dreaded call
In the months before the 2008 Democratic National Convention, local, state and federal officials planned for a worst-case event in Denver, including a biological attack.
Shortly before 9 a.m. on Aug. 28, the convention's final day, that frightening scenario seemed to have come true. That's when Chris Lindley, of the Colorado health department, got the phone call from a colleague, saying BioWatch had detected the tularemia pathogen at the convention site.
Lindley, an epidemiologist who had led a team of Army preventive-medicine specialists in Iraq, had faced crises, but nothing like a bioterrorism attack. Within minutes, chief medical officer Ned Calonge arrived.
Calonge had little faith in BioWatch. A couple of years earlier, the health department had been turned upside down responding to what turned out to be a false alarm for Brucella, a bacterium that primarily affects cattle, on Denver's western outskirts.
"The idea behind BioWatch — that you could put out these ambient air filters and they would provide you with the information to save people exposed to a biological attack — it's a concept that you could only put together in theory," Calonge said in an interview. "It's a poorly conceived strategy for doing early detection that is inherently going to pick up false positives."
Lindley and his team arranged a conference call with scores of officials, including representatives from Homeland Security, the Environmental Protection Agency, the Department of Health and Human Services, the Secret Service and the White House.
None of the BioWatch samplers operated by the state had registered a positive, and no unusual cases of infection appeared to have been diagnosed at area hospitals, Lindley said.
The alert had come from a Secret Service-installed sampler on the grounds of the arena where the convention was taking place. The unit was next to an area filled with satellite trucks broadcasting live news reports on the Democratic gathering. Soon, thousands of conventioneers would be walking from Pepsi Center to nearby Invesco Field to hear Obama's acceptance speech.
Had Lindley and Calonge been asked, they said in interviews, they wouldn't have put the BioWatch unit at this spot, where foot and vehicle traffic could stir up dust and contaminants that might set off a false alarm. As it turned out, a shade tree 12 yards from the sampler had attracted squirrels, potential carriers of tularemia.