Early warning systems for hazardous biological agents in potable water.

Abstract

Background There is a growing concern with the potential for terrorist use of biological weapons (bioweapons) to cause civilian harm (1-5) This concern has been focused around two assumptions: that a terrorist is most likely to effectively disperse bioweapons through air (3), and that we must be prepared to address terrorist use of bioweapons through treatment of affected individuals, with emphasis on strengthening the response of the health-care community (3,5,6). For the most part, concern has not focused on the use of bioweapons in drinking water systems (4,7), and much less attention has been paid to preattack detection than to postattack treatment. Threats to drinking water supplies have plagued humans since the dawn of history. These threats range from the spectacular and highly disruptive (e.g., floods, spills of oil or toxic chemicals) to the more mundane, but not necessarily less important, such as impacts from storm pipe discharges or runoff from agricultural lands. A recent conference, Early Warning Monitoring to Detect Hazardous Events in Water Supplies, held 17-19 May 1999 in Reston, Viriginia (8), concluded that terrorist use of bioweapons poses a significant threat to drinking water. Several pathogens (e.g., anthrax, Clostridium perfiingens, plague) and biotoxins (e.g., botulinum, aflatoxin, ricin) have been weaponized, are potentially resistant to disinfection by chlorination, and are stable for relatively long periods in water (7). Further, although water provides some dilution potential, any size neutrally buoyant particle, as well as sophisticated technologies such as microcapsules, can be used to disperse human pathogens in drinking water systems. Effectiveness of an attack can be enhanced through introduction of the bioweapon near the tap, such as in the distribution system (postdisinfection). Water storage and distribution systems also facilitate delivery of an effective dose of toxicant to a potentially very large population, as well as a lower-level chronic dose (for chemicals) with longer-term effects and lower-detection thresholds. Although the probability of a terrorist threat to drinking water is extremely low, the consequences could be very severe for exposed populations; thus, this conference concluded that national attention must be focused on detecting threats from biological terrorism, as well as other catastrophic events in drinking water supplies, and on preventing human exposure wherever possible. To that end, the conference concluded that technology-based and other pre-event or pre-exposure management strategies can be effective deterrents to widespread human exposure to bioweapons, as well as other low-probability/high-impact contaminant events in drinking water supplies, such as the introduction of Cryptosporidium (9). Of particular note are new and developing technologies to rapidly detect pathogens in real time, both in source water and water distribution systems. Included among these technologies are DNA microchip arrays (10), immunologic techniques (11), microrobots (12), and a variety of optical technologies, flow cytometry, molecular probes, and other techniques (13,14). None of these technologies is presently available commercially nor have any of the technologies been tested in large drinking water systems. However, this conference concluded that these technologies may be among the most effective approaches for early detection and warning of the use of bioweapons, as well as other catastrophic contamination events in drinking water systems, and encouraged their rapid development. Given that early detection technologies will likely be available in a few years, and that pre-exposure management, where it is successful, will prevent adverse health effects, it is prudent to address the myriad issues that are associated with the use of early detection and warning systems, as well as other preexposure management techniques. In this paper, we present characteristics of early warning systems (EWSs) and other pre-exposure management approaches that may increase the chances of preventing human exposure, if biological weapons are used in drinking water systems. We also address the interpretation of, response to, and communication of information derived from EWSs. This report reflects the deliberations of a breakout group from this conference that addressed system characteristics and interpretation, response, and communication issues.