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 perfringens, 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 pre-exposure 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.
Early
Warning Systems: Desirable Properties and Cost-Benefit Considerations
The goal of an early warning monitoring system is to reliably identify low-probability/
high-impact contamination events (chemical and radiation as well as microbial)
in source water or distribution systems in time to allow an effective local response
to prevent exposure. Although surveillance of infectious disease or other public
health effects is an important component of impact assessment in contamination
events, surveillance does not provide early warning, as it detects disease or
other impacts after they have occurred, often with a long lag time. Rather, an
EWS must detect a contamination event in a time frame that allows the implementation
of an effective response to reduce or avoid entirely the adverse impacts that
may result from the event. The development and implementation of EWSs are likely
to be costly and labor intensive; thus, several factors must converge to support
their use. Generally, local support for EWSs will occur when the cost and frequency
of false positives is less than the benefits of averting true positives. When,
on the other hand, the cost of monitoring exceeds any benefit from the use of
an EWS, it is unlikely that there will be support for the system. The extent
of the difference between benefits and costs that is required to support an EWS
will be determined at the local level and will likely differ among localities.
Local support will generally increase as the risk or perception of risk of serious
illness increases. Risk or the perception of risk will also increase as the presence
or effectiveness of existing barriers (e.g., chlorination for pathogens) decreases,
as the seriousness (perceived or real) of the potential illness increases, and
as the size of the affected population increases (among others). Regardless of
the cost-benefit ratio, the EWS must be reliable; that is, it must be sensitive,
specific, reproducible, and verifiable [as well as supported by appropriate quality
assurance/quality control (QA/QC) procedures]. It should minimize the potential
for both high numbers of false negative and false positive results. Additionally,
receptivity for EWS and their attendant costs will increase as the ancillary
benefits of the system increase. Systems that can detect and warn of many contaminants,
or that provide broad coverage of many parameters, will be more desirable than
systems that provide narrow coverage or detect relatively few parameters. However,
it is likely that EWSs that provide broad coverage will be more expensive to
operate and maintain than EWSs that provide narrow coverage; therefore, the cost-benefit
ratio for each system and decisions regarding desirability must be assessed at
the local level. Finally, systems that are easy to install and operate, that
provide continuous monitoring, that use standardized analytical equipment, and
that enhance source identification are likely to increase desirability. Continuous
monitoring reduces the likelihood that contamination events will be missed (although
it also increases the costs of equipment maintenance, data interpretation, etc.),
whereas standardized equipment can be more easily shared among users and repaired
and replaced than custom equipment.
Interpreting the Output of EWS
The most effective
use of an EWS will occur where there is a structured, well-defined approach to
the interpretation of data generated by the EWS and to the types of responses
that are triggered by data from the EWS. Interpretation of data from an EWS may
be particularly problematic. Determining when a response is necessary, based
on the performance of an EWS, requires a clearly established baseline for contaminants
or events of interest, and a clearly established deviation from the baseline.
Both the baseline and deviation from it that triggers a response must be determined
in advance of any contamination event, rather than in response to a particular
event. Ideally, both the baseline and deviation from it will be established at
the time of EWS installation. Baseline development will be contaminant or event
specific and will likely be influenced by the toxicity of a compound or pathogen,
the nature and extent of population or subpopulation exposure to the compound
as well as to similarly acting compounds or pathogens, by the ability to detect
the compound or pathogen (test sensitivity and specificity), and at least to
some extent by the perceived risks associated with exposure to the compound or
pathogen. In some cases, a maximum contaminant level (MCL) established by the
U.S. Environmental Protection Agency may be used as the baseline. However, MCLs
do not exist for most microbiological contaminants. In this case, a baseline
level must be developed. This can be done at the community level and should include
a variety of stakeholders including but not limited to scientists, public health
experts, emergency management officials, local politicians, and representatives
from the community at large. Establishment of a trigger (deviation from a baseline
that results in a particular response such as a "boil water" advisory)
will be influenced by the nature and magnitude of the adverse event (e.g., by
the extent of public health impact that could occur as a result of the contamination
event), by the nature of the action to be taken as a result of trigger exceedance,
and at least to some extent by the perceived risk of exposure to the compound
or pathogen. A stringent trigger (little difference between the baseline and
deviation from the baseline that triggers an action or response) may be appropriate
for events that have severe public health consequences. A less stringent trigger
may be appropriate for actions that have significant costs (monetary or others)
such as shutting down an entire water supply system to a large metropolitan area.
However, a stringent trigger may be appropriate even where an action has significant
costs, when a contamination event has a very severe public health impact, or
where the perception of risk is very high. Finally, trigger development must
be influenced by the sensitivity and specificity of the test; that is, triggers
must be developed to minimize both false positives and false negatives associated
with the analytical methodology. A confirmation step, which does not necessarily
preclude action, should also be included in the interpretation process for EWSs.
Where a trigger is exceeded, steps should be taken to confirm the exceedance.
Confirmation may include resampling or intensified sampling and analysis, duplicate
analyses, and other QA/QC procedures. Depending on the nature of the contamination
event and on the potential public health impacts, an action may or may not be
taken until a confirmation process has been implemented and appropriate results
provided. Clearly, where there are severe public health consequences, action
should not await confirmation. However, subsequent actions, or delays in implementing
them, may be influenced by the outcome of confirmatory steps. Where there is
a high number of false positives (determined as a result of the confirmation
step), subsequent actions based on trigger exceedance may be delayed. Additionally,
a high number of false positives should trigger an assessment of the analytical
equipment and methods, to determine the causes of the high false-positive rate
and to identify improvements in the equipment and methods to reduce false positives.
Response and Communication
Many responses are possible when an alarm is triggered by an early warning monitoring
system. Responses may include modification to the drinking water system (shutdown,
addition of disinfectants, etc.), notice (boil water advisory) either to the
general public or to target communities or subpopulations, additional data gathering
or monitoring, follow-on surveillance and epidemiologic studies, no action, and
some combination of these, among others. The type of response will be dependent
on the nature of the threat and the nature of the drinking water system, including
the population served by it. For example, a response to a threat received by
phone may differ from a response detected by an EWS. For a phone threat, a determination
of credibility may be necessary prior to performing a response. Where an EWS
is in place, credibility of the threat may be judged by the performance of the
EWS itself, when it is capable of detecting the contaminants included in the
threat.
Where an EWS is not in place, additional steps may be necessary to judge
credibility and to determine the appropriate response. Steps may include monitoring
for the contaminant at appropriate locations in the source water or distribution
system, and monitoring for surrogate parameters that may indicate contamination
(e.g., increased chlorine demand, changes in pH). Additionally, law enforcement
representatives and psychologists may provide insight into the credibility of
the threat.
Regardless of their nature, a critical component to the success of
any EWS is the preparation of a process or plan that provides guidelines for
the type and extent of response to all potential threats. The plan must be developed
in advance of the threat and preferably concurrent with the development of the
EWS. In effect, the plan should be considered part of a comprehensive emergency
planning process for a variety of threats to public health, both waterborne and
non-waterborne. The emergency response plan must be developed with the participation
of all major stakeholders.
Some stakeholders include:
• Individuals with specific expertise (e.g., microbiologists, toxicologists)
• Politicians/community leaders
• Health department, hospital representatives, other health care professionals
• Representatives of the local water utility
• Representatives of water regulatory agencies (local, state, and federal)
• Representatives of high-risk groups
• Staff from the wastewater treatment plant
• Major water users and processors
• Law enforcement agencies
• Psychologists
• Other emergency preparedness groups (e.g., fire department)
• Representatives of sources that pose potential threats to the drinking
water system
There is extensive experience with the development of emergency
response
plans that can be drawn upon by communities interested in implementing an early
warning monitoring system. The U.S. Centers for Disease Control and Prevention,
U.S. Federal Emergency Management Agency, the National Infrastructure Protection
Center of the Federal Bureau of Investigation, and the Emergency Management and
Emergency Preparedness Office of the U.S. Health and Human Services offer guidelines
for emergency response plan development. Approaches to postevent response have
also been developed (3,5,6). The nature and extent of communication of the threat
to the affected population should also be guided by the emergency response plan.
A chain of communication should be established as part of the plan, from the
point where information of the threat is received to the final implementation
and communication of the response to the threat. Experts from the local utility
and representatives from the health care community, hospitals, law enforcement
agencies, and other emergency preparedness groups should be included in the chain
of communication. A particularly delicate matter is the communication of the
existence of the EWS prior to any threat that it detects. It is conceivable that
awareness of the EWS and its goal may stimulate a few individuals to perform
acts that threaten the drinking water system or its users. Therefore, the existence
of the EWS must be put into the context of preparations for a variety of events
including floods, tornadoes, earthquakes, etc. It should not be advertised simply
as a technology designed to address terrorism or other intentional or unintentional
threats. The EWS must be framed in a positive manner by emphasizing the importance
of real-time monitoring for a variety of chemicals and pathogens, designed to
better understand all potential threats to the system and consumers. Additional
steps to raise positive awareness of the EWS include general community education
about where drinking water comes from, how it is handled at the treatment plant,
and how it is dispersed in the community (without providing enough information
to highlight a system's vulnerability). Tests of preparedness for and response
to water emergencies (akin to testing the tornado sirens) should also be conducted
and publicized in the community. Again, these tests should be cast in a positive
light, with emphasis on general preparedness rather than on preparations for
specific events.
Conclusions
An EWS must reliably identify low-probability/high-impact contamination events
in source water or distribution systems in time to allow an effective local response.
The type and nature of the response, and the method of communication of the response
will be dependent upon the type and nature of the threat, on the characteristics
of the EWS itself, and on the nature of the affected population.
Critical to
the successful development, implementation, and use of an EWS is strong community
support for the system. This support must be derived from aggressive education
activities regarding community drinking water supplies, and from active participation
of community members and stakeholders in the development and implementation of
the EWS. Especially critical is the development of an emergency preparedness
plan that guides the type of responses associated with a signal from the EWS
and the communication of actions based on the responses. The resources necessary
for the development, installation, operation, and maintenance of an EWS will
be substantial; therefore, virtually all of the decisions regarding the EWS must
be made at the local or community level. This includes the type of EWS to install
(and its attendant costs), interpretation of information from the EWS, responses
that should occur as a result of a signal from the EWS, and the nature of communications
to the affected public. The emergency preparedness plan will play a crucial role
in many of these decisions, and there should be significant local involvement
in the development of the plan. However, funding assistance for EWS development,
installation, and operation may be available from both the state and the federal
government. Extensive guidance is also available from a variety of federal agencies
on the development of emergency response plans. An EWS should not preclude actions
to ensure or strengthen the security of drinking water systems in every community.
Points of vulnerability in both source water and distribution systems should
be identified in each community, and steps taken to reduce the vulnerability
at these points. Steps may be as simple as securing hydrants or other entry points
to the distribution system, or installing improved security around treatment
and storage facilities. These and many other simple steps may significantly reduce
system vulnerability as EWSs are developed and as their costs decrease, so that
they may be available to all communities, regardless of size and resources.
There
are also sociological issues that must be addressed as technological and non-technological
approaches are implemented. This conference concluded that a threat (whether
real or a hoax) to a drinking water system may pose as much problem as a terrorist
act, and response plans should consider how to address potentially unrealized
threats. Further, individuals involved in efforts to protect drinking water must
be cognizant of the ramifications of the effort itself; even discussion of potential
terrorism in drinking water systems, such as through this paper, must be done
carefully so as not to provide a stimulus for the act. To ensure the full protection
of drinking water, or other media, a technology-based early warning monitoring
system should be just one component of a comprehensive program to protect the
public from biological terrorism and other low-probability/high-impact contamination
events, whether they occur in air, water, or food.
The program must also include
physical, social, and economic steps to prevent the problem, as well as follow-up
monitoring to ensure that early detection of disease will occur if a monitoring
system or other steps fail.
References and Notes 1. Burrows WD, Valcik JA, Seitzinger
A. Natural and terrorist threats to drinking water supplies. In: Proceedings
of the 23rd Environmental
Symposium, 7-10 April 1997, New Orleans, Louisiana. 2. Lederberg J. Infectious
disease and biological weapons: prophylaxis and mitigation. JAMA 278:435-438
(1997). 3. Simon JD. Biological terrorism: preparing to meet the threat. JAMA
278(5):428-430 (1997). 4. Ableson PH. Biological warfare. Science 286:1677 (1999).
5. Waeckerle JF. Domestic preparedness for events involving weapons of mass destruction.
JAMA 283(2):252-254 (2000). 6. Macintyre AJ, Christopher GW, Eitzen E, Gum R,
Weir S, DeAtley C, Tonat K, Barbera JA. Weapons of mass destruction events with
contaminated casualties. JAMA 283(2):242-249 (2000). 7. Burrows WD, Renner SE.
Biological warfare agents as threats to potable water. Environ Health Perspect
107:975-984 (1999). 8. Brosnan TM, ed. Proceedings of the Conference on Early
Warning Monitoring to Detect Hazardous Events in Water Supplies, 17-19 May 1999,
Reston, Viriginia. Washington, DC:ILSI, 1999. 9. Mackenzie WR, Hoxie NJ, Proctor
ME, Gradus MS, Blair KA, Peterson DE, Kazmierczak JJ, Addiss DG, Fox KR, Rose
JB, Davis JP. A massive outbreak in Milwaukee of Cryptosporidium infection transmitted
through the public water supply. N Engl J Med 331:161-167 (1994). 10. Betts KS.
DNA chip technology could revolutionize water testing. Environ Sci Technol 33(15):300A-301A.
(1999). 11. Betts KS. Testing the waters for new beach technology. Environ Sci
Technol 33(16): 353A-354A (1999). 12. Hewish M. Mini-robots sniff out chemical
agents. Jane's IDR, Features (2000). 13. Pelley J. Rapid, genetic-based test
can identify human viruses in beach water. Environ Sci Technol 33(18):399A (1999).
14. Sobsey M. Methods to identify and detect microbial contaminants in drinking
water. In: Identifying Future Drinking Water Contaminants. Washington, DC:National
Academy Press, 1999;177-203. [ EHP-in-Press ] [ Citation in PubMed ] [ Related
Articles ] Last Updated: Septermber 11, 2000 
