Christian Mittermayr
2.4 RISK ANALYSIS OF BIO-TERRORISTIC ATTACKS ON DRINKING WATER SYSTEMSWATER SYSTEMS
2.4.1 Threat assessment
Deliberate food and water contamination remains the easiest way to distribute biological agents (microorganisms or biological toxins) for the purpose of terrorism. Because biological agents are often easily accessible, can be delivered concealed, are easy to transportation, have high potency and are difficult to identify there is a risk that they are used to gain political advantages by terrorists.
Usually a small number of large drinking water utilities located primarily in urban areas provide water services to the majority of a countries population. These systems represent the greatest targets of
opportunity for terrorist attacks, while the large number of small systems are less likely to be perceived as key targets by terrorists who might seek to disrupt water infrastructure systems (Stephenson, 2004;
Copeland, 2010).
Thetype and category of adversaryas well as the type of impact sought will have an important role on the agent-selection principles. For examples, for non-state entities, accessibility, not overall aggressiveness and stability in storage, might be the dominant criterion in their choice of agent. Therefore, the rank order in which public health authorities assess the different agent threats may not be the same as that of military authorities (WHO, 2004; DHS & FBI, 2008).
The WHO (2004) divides the criteria for the pathogen selection into two broad categories
• Acquisition, production and dissemination of the contaminants
• Biological properties of the contaminant and its interaction with the host but they have to be considered together, since many of these criteria show interactions.
Technical constraints on use
The ability to conduct attacks using contagious agents requires the possession of a viable pathogenic bacteria or virus in sufficient quantity to cause a communicable disease. Characteristics of acquisition, production and dissemination are determined by:
• Access to Agent
• Ease of cultivation
• Storage security
• Stability during handling and storage
• Dissemination method
• Establishing field dosages
• Routes of exposure
Access to agent/sources of agent
Gaining access to biological agents never appears to have been a significant limiting factor. In fact, acquiring biological agents has usually proven to be relatively easy. In a few cases, pathogens were acquired from culture collections, usually legitimately but sometimes not, while the perpetrators usually produced toxins.
The effectiveness of biological agents depends heavily on the specific strain of the organism, and it may be difficult to acquire the more dangerous strains relying on natural sources. Despite efforts to restrict the illicit acquisition of biological agents, it is likely that terrorists and criminals will be able to obtain the agent that they want when they want it. If unable to acquire from a legitimate culture collection or a medical supply company, they can steal it from a laboratory. If unable to steal it, a group with the right expertise could culture the agent from samples obtained in nature. Many biological agents are endemic, and a skilled microbiologist would have little difficulty in culturing an agent from material taken from the environment (Carus, 2001).
Ease of cultivation
Some pathogens are easy to culture, while others are extremely difficult. Some agents would require further processing to use in an attack. Particularly, viruses are very hard to culture in big quantities, while bacteria can easily be produced in large quantities in simple containers. Skill is one of the most important parameter to grow larger quantities of an agent.
Risk analysis of bio-terroristic attacks on drinking water systems 13
Storage security
The use of highly contagious diseases may be the easiest way to cause mass casualties, from a technical perspective. However, such agents pose risks for the group using them and could have an impact on people that the perpetrators do not want to affect (Carus, 2001).
Stability during handling and storage
Some biological agents die or lose virulence once released. The implications of these variables will differ from one organism to the next and the environmental conditions. Perpetrators have to have sufficient knowledge about this factors in order to launch an successful attack (Carus, 2001).
Dissemination methods
The WHO (2004) lists several dissemination methods for biological agents:
• Airborne (inhalation)
• Drinking water (ingestion)
• Food (ingestion)
• Arthropod vectors
• Direct
Based on his analysis of over 200 past incidents of chemical and biological terrorism, McGeorge (1986) concludes that“Dissemination devices or means have typically been very simple in design or procedure and of corresponding low efficiency.”The three most common dissemination routes according to Purver (1995) were:
(1) Contaminated food or drink (43%) (2) Contaminated consumable products (13%) (3) Contaminated water supplies (12%)
If a simple dissemination technique is employed, relatively little technical expertise is needed. For example, limited skill is required if the perpetrators can inject agent directly into their victims or if they seek to contaminate food. Many pathogens that have had a significant impact on human life, such as Vibrio cholerae andSalmonella typhi, are water-borne. Thus, using a municipal water systems to disseminate pathogens might seem promising to terrorists. On the other hand, it is very difficult to infect a large population through deliberate contamination of water supplies (Carus, 2001).
Establishing field dosages
The ability to generate a minimum concentration of agents over a predictable area must be evaluated.
Routes of exposure
The pathogens can enter the body in several ways:
• Through the respiratory system
• Through the skin
• Through the oro-nasal mucosal tissue and the conjunctiva
• Through the digestive system
The biological agents can enter thedigestive systemvia contaminated food or drinking-water, by hand– mouth contact after touching contaminated surfaces, or by swallowing of respiratory mucus after the
accumulation of larger aerosol particles in the nose, throat and upper airways. Of all exposure routes, entry through the digestive system is the easiest to control, provided that the contaminated sources are known (or at least suspected). Simple hygienic measures and control of supplies of food and drinking-water can significantly reduce the risk of exposure (WHO, 2004).
Characteristics of biological agents
The chief characteristic of biological agents is their ability to multiply in a host. It is this that gives them their aggressive potential. Contraction of the disease results from the multifactorial interaction between the biological agent, the host (including the latter’s immunological, nutritional and general health status) and the environment (e.g. sanitation, temperature, water quality, population density). The WHO (2004) lists the following relevant biological characteristics:
• Infective Dose/Dose Response Curve
• Lethality
• Virulence
• Incubation period (rapidity of effect)
• Contagiousness (infectivity) and mechanisms of transmission
• Stability of Storage (resist degradation during handling and storage)
• Resistance to Environment and Water Treatment (chlorine, chloramines,…)
• Resistance to medical Treatment of Patients Infective dose/dose–response curve
Dose–response models estimate of the probability of an infection given a specific dose of a defined pathogen. The concept of the single-hit principle, where even a single pathogen may be able to cause infection and disease, supersedes the concept of a (minimum) infectious dose that is frequently used in older literature.
Available dose–response data have been obtained mainly from studies using healthy adult volunteers.
However, adequate data are lacking for vulnerable subpopulations, such as children, the elderly and the immune-compromised, who may suffer more severe disease outcomes. It is crucial to note that any model will depend very heavily on the strain, particularly the presence of the virulence factors, and on the health of the individual host (Carus, 2001).
The infectious doses are independent of victim bodyweight because the pathogen reproduces in the host, so the potency of the pathogens on a weight basis exceeds that of the most toxic chemicals;
between a few and a few thousand viable organisms is all that is required to produce infection in many cases (Purver, 1995).
Lethality
Lethality reflects the ability of an agent to cause death in an infected population. The case-fatality rate is the proportion of patients clinically recognized as having a specified disease who die as a result of that illness within a specified time, for example, during outbreaks of acute disease (WHO, 2004).
Virulence
Virulence is the relative severity of the disease caused by a microorganism. Different strains of the same species may cause diseases of different severity. Some strains ofFrancisella tularensis, for example, are much more virulent than others (WHO, 2004).
Risk analysis of bio-terroristic attacks on drinking water systems 15
Incubation period
The incubation period is the time elapsing between exposure to an infective agent and the first appearance of the signs of disease associated with the infection. This is affected by many variables, including the agent, the route of entry, the dose and specific characteristics of the host (WHO, 2004).
Contagiousness
For those infections that are contagious, a measure of their contagiousness is the number of secondary cases arising under specified conditions from exposure to a primary case. The mechanisms of transmission involved may be direct or indirect. Thus transmission may, for example, result from direct contact between an infected and an uninfected person, or it may be mediated through inanimate material that has become contaminated with the agent, such as soil, blood, bedding, clothes, surgical instruments, water, food or milk (WHO, 2004).
Stability of storage
Stability of storage determines how long under which conditions the biological agents can stored and transported (WHO, 2004).
Resistance to environment & treatment
The agents have to be resistant to environmental factors such as water temperature, lack of nutrients in drinking water, surface forces, residual concentration of disinfectants and so on. In the case the contamination takes place before the water treatment plant, the microorganisms have to be resistant to for example, chlorination or other treatment methods. On the other hand, treatment plants can be overwhelmed by large spikes in pathogen concentration and render the treatment ineffective (Clark, 1980; Purver, 1995).
Resistance to medical treatment of patients
Terrorists also might consider how easy it is to treat an infection as soon as it is detected and identified. The shock might be even bigger when the public learns that there is no efficient treatment available to those that have been exposed. Most bacterial infections can be easily treated by antibiotics unless terrorists chose or genetically-engineered pathogens that are resistant to many antibiotics. Very often there is no medication for viruses and only very few to eukaryotic parasites, or only with significant side-effects.
Selection of pathogens
In the present study, the potential contaminants for the water supply system have been compiled by applying a two-step procedure proposed by the WHO (2004) amended with extra criteria. The procedure first tries to compile a list with the broadest possible coverage. In most instances, the lists do not consider the dissemination method or prioritize airborne dissemination. In the second step, the list is narrowed down to those agents that are of concern for the water supply system.
The list of harmful pathogens with the broadest possible coverage information is compiled from Field (2004) and Schmidet al.(2008) using data
• Frombroad treaty definitionsof biological weapons
• Fromagent liststhat have been negotiated to facilitate treaty implementation, or proposed therefore
• From historical data about agents that
○ Have been weaponised or stockpiled in recent times
○ Are known to have been used as weapons
○ Have been used in non-state entities/biocrimes
• Fromepidemiological data on natural occurring drinking-water and food contaminations
Several publications have assessed the potential of pathogens for use in contaminating the water distribution system (US Army, 1998; Burrows & Renner, 1999; Hickmann, 1999; Khan et al. 2001;
Field, 2004; Shea & Gottron, 2004; Ottaviani et al. 2005; Gleick, 2006; Nuzzo, 2006; EPA, 2007;
Winston & Leventhal, 2008; Clark, 2010; Burrows & Birkmire, 2011). Adding epidemiological data on natural drinking-water contaminants, a final list of potential biological contaminants for the drinking-water system has been compiled (see Table 2.1). A similar effort was conducted by the Austrian Agency For Health And Food Safety (AGES) (Schmidet al.2008) which found a total of 180 species considered as potential bio-terroristic agents. 55 pathogens were included in the short list but no special consideration was given to pathogens that could potentially be used for contaminating the drinking water system.
International treaties
The broadest catchment of agents of concern, and therefore the starting point for the selection process, is to be found in the treaties that outlaw the possession of biological and chemical weapons. The BioWeapons Covention (BWC), which is a legal instrument, contains lists which have been developed for inclusion in the BWC Protocol. The purpose of these lists would again be to exemplify, but not to define, the scope of the general-purpose criterion (WHO, 2004).
Agent lists
The WHO collected a comprehensive list of agents that have been listed in various treaties. This list already shows how much variation there can be in different agent assessments (WHO, 2004). Another list of bio-terroristic agents has been compiled by the CDC (2012). The agents are categorized with respect to their danger. Category A agents of the CDC are mostly for airborne transmission, therefore also Category B agents of the CDC should be included when considering water contamination.
The United States Departments of Health and Human Services and of Agriculture compiled the“Select Agents and Toxins List”which have the potential to pose a severe threat to both human and animal health, to plant health, or to animal and plant products (HHS & USDA, 2008).
Historical data
Purver (1995) summarizes historical data on agents that have been weaponised or stockpiled in recent times or are known to have been used as weapons and McGeorge (1986) and Carus (2001) compiled information on agents that have been used in non-state entities/biocrimes.
Historical records are not complete, however, because former possessor states have not yet made all of the relevant papers available. Nevertheless, the WHO (2004) compiled an extensive list of antipersonnel agents.
The information on the actual use of toxic and infective agents for hostile purposes may be even less complete than that on weaponization or stockpiling, not least because of the role of these agents in clandestine warfare, on which official records are often sparse.
Biocrimes
Terrorists and criminals may not use the same agents as those selected by military biological weapons programs (Carus, 2001). Although there are differences between terrorist and criminal uses of biological agents, the biocriminal faces many of the same obstacles as the bioterrorist. Both must acquire, develop, and employ biological weapons, so the technical constrains that appear in criminal cases are likely to apply for terrorist cases. In addition, it is possible that criminal cases will be a leading indicator of possible terrorist interest in biological agents. Nevertheless, the differences between terrorists and Risk analysis of bio-terroristic attacks on drinking water systems 17
Table2.1Shortlistofpathogensrepresentingarisktothedrinkingwatersystem. PathogenWater threatStable inwaterInfectiousdoseExposureChlorine tolerance Bacteria Bacillusanthracisyes2yearsspores6000inh.Sporesresistant Campylobacterjejuniyes400–500 Escherichiacoli– enteropathogenic(EPEC)yesforinfantsthedoseis verylow. Inadults:.106 total dose Escherichiacoli– enterotoxigenic(ETEC)yes108 –1010 Franciscellatularensisyes,90days100,000,000ing.Inactivated,1ppm, 5min Salmonellaspp.(typhoid)yes8days,fresh water15–20/10,000ing.inactivated Shigellaspp.(S.dysenteriae, S.flexneri)yes2–3days10/10,000ing.Inactivated,0.05 ppm,10min Vibriocholeraeyes“Surviveswell”1000ing.“Easilykilled” VibriocholeraeO1yes106 Yersiniapestisyes16days500inh.Unknown Plesiomonasshigelloidesyes.106 Brucellaspecies (B.Melitensis,B.Suis)probable20–72days10,000uns.Unknown Aeromonashydrophilaand otherspp.possiblyunsuccessfuleven athighdoses Chlamydiapsittacipossibly18–24h,seawaterUnknownUnknown CoxiellaburnetiipossiblyUnknown25uns.Unknown
Escherichiacoli– enteroinvasive(EIEC)possiblypossibly≥10 EscherichiacoliO157:H7 enterohemorrhagic(EHEC)possiblypossibly≥10 Listeriamonocytogenespossibly,103 Vibriocholeraenon-O1possibly.106 Yersiniaenterocoliticaand YersiniapseudotuberculosispossiblyUnknown MiscellaneousentericspossiblyUnknown Clostridiumperfringensno/probableCommonin sewage5×105 /≫108 ing.Resistant Protozoa CryptosporidiumparvumyesStabledays1/130ing.Oocystsresistant Entamoebahistolyticayesoneviablecyst Giardialambliayesoneormorecysts Viruses entericvirusyes8–32days6ing.Readilyinactivated (rotavirus) HepatitisAyesUnknown30/10–100virus particlesInactivated,0.4ppm, 30min HepatitisEvirusyesUnknown Norwalkvirusgroupyespresumedtobelow Rotaviruspossibly10–100infectious viralparticles Variolapossiblyunknown10uns.Unknown Source:DatafromBurrowsandRenner(1999);FDA(2011)andCDC(2012).
Risk analysis of bio-terroristic attacks on drinking water systems 19
criminals suggest that caution needs to be exercised in extrapolating from the experience of criminals to that of terrorists.
Carus (2001) analyzed 180 cases of illicit biological agent use and the number of criminal cases is higher than that of terrorist cases.
Confirmed use and confirmed possession and probable use of agents
In Table 2.2, below, a compiled list of biological agents previously used or found in possession of possible perpetrators.
Bacterial agents: Note that only three of cases involved possession of anthrax. Yersinia pestis,S. typhi, and Shigella dysenteriae strains appear several times, while seven other pathogens appear no more than once.
Viral agents: Few perpetrators have considered viral agents, except when they can use it in a natural state.
HIV appears in several cases, including at least four murder cases.
Other pathogens: Only one case involved the use of a parasite. In that case, the perpetrator contaminated food withAscaris suum, a worm that infects pigs and does not normally infect humans.
Naturally occurring microbial water contaminants
Naturally occurring microbes are potential agents that can be used to intentionally contaminate the drinking water system (Ashfordet al.2003). National drinking water standards, like those from the EPA (2012c), give an indication on which microorganisms are considered to be a particular threat to the public health.
Their occurrence is usually monitored and regulated.
In the U.S.A., the EPA produces the drinking water“Contaminant Candidate List”(EPA, 2012a). The contaminants on the list are known or anticipated to occur in public water systems. However, they are Table 2.2 Confirmed use and confirmed possession and probable use of agents.
Agent
(human pathogen)
Confirmed use Threatened use
(confirmed possession)
Probable or possible use
Total
Salmonella typhi 5 1 6 12
Bacillus anthracis 3 2 2 7
HIV 3 4 7
V. cholera 1 3 4
Yersinia pestis 1 1 2
Shigella 2 2
Salmonella typhimurium 1 1
S. paratyphi 1 1
M. bovis? 1 1
Y. enterocolitica 1 1
C. botulinum,C. tetani 1 1
Yellow fever virus 1 1
Hepatitis A virus 1 1
Giardia 1 1
Source: Data were from Carus (2001).
unregulated by existing national primary drinking water regulations. Additional sources of information are the various epidemiological data in relation to water-borne and food-borne outbreaks of infectious diseases.
A special issue of the Journal of Water and Health was published in July/August 2006 by EPA (2006) with a series of review articles on endemic gastrointestinal illnesses associated with microbial drinking water exposures.
Other relevant legal frameworks are national regulations for microbial food contaminants and information provided by government agencies on potentially hazardous microorganisms. The US Food and Drug Administration FDA compiled the“FDA Bad Bug Book”(FDA, 2011). It lists and describes microorganisms that are harmful for the food and water supply system. Monroe (2006) reorganized the table and created a rating on the propensity of each pathogen to be waterborne.
Assesment of biological agents with respect to drinking-water attacks
There are several publications that assess which biological agents can be used for attacks on the drinking water supply (Burrows & Renner, 1999; Hickmann, 1999; Khan et al. 2001; Field, 2004; Shea &
Gottron, 2004; Ottaviani et al. 2005; Gleick, 2006; Nuzzo, 2006; EPA, 2007; Winston & Leventhal, 2008; Clark, 2010; Burrows & Birkmire, 2011).
Burrows and Renner (1999) compiled one of the most comprehensive investigations of biological threats to the drinking water system. A very useful summary contains information on: clinical considerations, infective/toxic dose, environmental stability, disinfection efficacy, removal by treatment systems.
2.4.2 Criticality assessment
Although the actual number of known victims and fatalities from bioterrorism and criminal activities has been miniscule compared with many other daily hazards, biological agents have the potential to poison or compromise our food or water supply, to severely damage segments of the economy, to cause human mass casualties and, perhaps most damaging, disrupt our society physically and psychologically.
An unintentional drinking-water contamination event that occurred in Tel Aviv, Israel in July, 2001 showed no matter how minor the contamination event or short-term the disruption of delivery of safe drinking-water, psychological, medical and public health impact could be significant (Winston &
Leventhal, 2008).
Thus, water systems have been designated as critical to national security by many governments.
The severity of the attack depends on the number of people affected, the individual exposure and the dose-response function of the contaminant.
2.4.3 Vulnerability assessment
Previous naturally occurring food- and waterborne outbreaks have demonstrated the vulnerability of both the water supply and the public’s health to biological contamination of drinking water. Such experiences suggest that a biological attack, or even a credible threat of an attack, on water supplies and water distribution systems represent potential targets for terrorist activity.
The vulnerability is characterized by the ease with which threat agents can be introduced in quantities sufficient to achieve the attacker’s purpose once the target has been reached.
The vulnerability is characterized by the ease with which threat agents can be introduced in quantities sufficient to achieve the attacker’s purpose once the target has been reached.