A cutting-edge biological terror alert system detected a potential threat in the air one morning back in 2008, threatening to derail then-Sen. Barack Obama’s acceptance speech in Denver for his party’s presidential nomination at the Democratic National Convention. Initial results from a pricey national air sampling system suggested that bacteria that could cause tularemia had been detected. The microbe, Francisella tularensis, might have been weaponized to cause the infectious disease.

Public health officials sprang into action and tested further samples from the area that triggered the system, but turned up negative results. The alert, like others issued by the system in the past decade, was ruled to be a false alarm. Obama still made his acceptance speech that night, of course, in an open-air stadium as planned. But the system’s critics say BioWatch has repeatedly triggered an alarm when no threat has existed. Now the program faces the scrutiny of Congress.

BioWatch, an alert system designed to be an early detection system for airborne threats such as anthrax and smallpox, was unveiled in 2003 by Pres. George W. Bush. In his State of the Union address, he talked about the system, saying he was, “deploying the nation's first early warning network of sensors to detect biological attack.” Since then the system has cost $1 billion and been met with mixed reviews. A committee convened by the Institute of Medicine (IOM) and the National Research Council (NRC) said in a 2011 report no expansion of the program should be made without better collaboration with the existing public health system. The panel also called for further analysis of the program and how it could be used to reduce mortality and morbidity.

The network of outdoor and select indoor air samplers was installed, under the aegis of the U.S. Department of Homeland Security (DHS), in more than 30 U.S. metropolitan areas to sniff the air for potential threats. The filters from those aerosol collectors are retrieved for analysis in state or county public health laboratories.

Whereas technically the potential threats detected by the system in the past were not false positives—they did accurately pick up tiny, background amounts of DNA from organisms naturally present in the environment— in effect, they were false alarms because they signaled the potential occurrence of a terrorist attack when none had occurred. Some public health officials have said they are hesitant to rely on the program. Others say it is an important piece of the bioterror response puzzle.

“The way I look at BioWatch is that it is a tool,” says Umair A. Shah, executive director of the Harris County Public Health and Environmental Services Department in Texas. “It is one of many tools that are available to public health decision—makers and needs to be kept in the context of that paradigm. The sum of all those tools is really how we go about making sound public health decisions.” Sensors in area around Houston and Harris County had the first-ever positive result through BioWatch in 2003. Like the later DNC incident, BioWatch picked up indications of F. tularensis. Those readings also turned out to be a false alarm; BioWatch again had detected organisms naturally present in the environment.

The value of the system, even with its false alarms, is that it could give public health officials the first clues of a bioterror attack. “You don’t necessarily want to make [BioWatch] less sensitive to avoid false positives,” says Seth Foldy, a physician who works on public health informatics and served on the NRC–IOM panel looking at the program. The tricky part, he says, is finding a way to make the system sensitive enough so that it would pick up actual disease-causing agents in the event of a bioterror threat, but specific enough to be able to distinguish them from very closely related bacteria that may exist in the environment but do not lead to human disease.

A House subcommittee is set to examine the program Tuesday, with representatives from the DHS and the U.S. Centers for Disease Control set to discuss the system's future. “The BioWatch Program is the only federally—managed, locally—operated nationwide bio—surveillance system designed to detect select aerosolized biological agents,” says DHS spokesman SY Lee. “BioWatch provides public health officials with a warning of a biological agent release, before potentially exposed individuals develop symptoms of illness.”

Against the backdrop of lukewarm reviews, however, a planned expansion of BioWatch, Generation 2.5, was canceled in fall 2008. The next proposed stage of the system, Generation 3, will be under discussion at the hearing. The system as it stands now is designed so that the time between sample collection and laboratory results indicating potential biological aerosol release is between 10 to 36 hours. With future iterations of the program the hope is to get initial analysis of the samples wrapped up within six hours. For Generation 3, DHS is looking into including autonomous biodetection technology to help eliminate the need for manual filter retrieval and analysis. Still, confirmatory tests would still be required raising questions about how much time would be saved and if it would result in faster response times and disbursement of emergency drugs that could help avoid human sickness or death.

At the very least it may help preliminary results get out faster. “The difference it would make,” says Bob England, director of the Maricopa County Department of Public Health, which covers the Phoenix metropolitan area, “is you would get your first inkling that something might be going on hours earlier. That would give you that much more time to get people together and ready to evaluate the confirmatory results when they do come back so it does make the response earlier.”

In the current fiscal environment there is also concern from some public health offices that dollars allocated to detecting biological threats through BioWatch may be competing with the ones needed to provide complementary information to help detect threats—such as picking up any uptick in certain symptoms at hospitals through robust health surveillance. According to National Association of County and City Health Officials (NACCHO), 59 percent of local health departments rely exclusively on federal funding to support their emergency preparedness programs. As cuts have been made to public health emergency response in recent years, says Jack Herrmann, senior advisor and chief of public health preparedness at NACCHO, that makes it more difficult to conduct consistent public health monitoring and create optimal response plans.