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CHAPTER 1
INTRODUCTION
The death rate in the industrialized world has decreased dramatically since consistent mortality records have been kept (Figure 1.1). A key feature of this improvement has been a major reduction in the infant death rate, which is the largest single contributor to our lengthening life expectancy. Reduction in the occurrence of waterborne diseases such as cholera, typhoid and other diarrheal diseases has contributed substantially to reducing the infant death rate, with the largest incremental improvements coming during the early 1900s.
In contrast, we continue to experience a devastating toll of illness and death in many of the most populous regions of the globe. The World Health Organization (WHO) estimates that 2.1 million people die every year from diarrheal diseases (including cholera), that the majority of these deaths is among children in developing countries and that 65% of these fatalities could be prevented by water, hygiene and sanitation interventions (WHO, 2002). The focus of this book is on the ability of fecal-oral disease transmission via drinking water to render drinking water unsafe. The context of drinking water transmission within the whole range of fecaloral disease transmission is shown in Figure 1.2.
The stark contrast between the experience in industrialized countries and that in the rest of the world demonstrates the enormous benefit that is achieved by implementing and maintaining effective practices for producing safe drinking water. Unfortunately, success can breed complacency. We have had and continue to have serious outbreaks of waterborne disease in affluent nations. Reviewing the cases presented in this book reveals in hindsight that these outbreaks were preventable. Similar outbreaks should not reoccur if we learn the lessons these cases have to offer. Perhaps more disturbing is the number of cases that were eminently preventable with even a minimal degree of foresight (e.g., Walkerton and North Battleford). The challenge is to convert hindsight into foresight.
In fairness to those involved in these failures, the means for prevention are always more obvious in hindsight. Reading the detailed accounts revealed at the Walkerton (O'Connor, 2002a) and North Battleford (Laing, 2002) Inquiries is disturbing because some of the oversights or failures described could conceivably happen to most people, on a bad day. Problems arise when small individual mistakes are allowed to accumulate; elements of failure gradually evolve into dangerous circumstances without revealing a clear warning of the scope of emerging disaster.
Although the literature is filled with reports of waterborne outbreaks, in a number of cases these accounts do not appear to have reached the consciousness of enough of those who are responsible for providing drinking water. Even the overwhelming publicity about the Walkerton tragedy in Canada was insufficient to prevent another major Canadian outbreak 11 months later in North Battleford: many of the same elements of failure contributed to the later outbreak.
These revelations are not recent. Consider the following quote from Edwin C. Lippy:
The disturbing trend toward more frequent occurrence of waterborne disease outbreaks should serve as a warning to all who share in the responsibility for the delivery of a safe and potable water. The 'multiple barrier' concept that relies on placing protective systems between the water consumer and actual as well as potential sources of contamination should be emphasized, with appropriate consideration for natural features (distance, dilution, geologic factors), man-made facilities (adequate waste treatment, water treatment, operational considerations) and conscientious surveillance by regulatory agencies (monitoring, inspection, certification).
This statement could have been written, with little modification, as an overview commentary for either of the Walkerton or North Battleford Inquiry reports; it was published in 1981 concerning the investigations of three U.S. outbreaks in 1979 (Lippy, 1981).
The number of things that can be wrong or go wrong without having an outbreak is both striking and troubling. The positive news is that a multiple barrier approach makes an outbreak much less likely. Some may argue that affluent societies are chasing diminishing returns by invoking more stringent measures to prevent outbreaks that are already infrequent. Certainly there are many environmental health issues where the pursuit of trivially small risks can be futile (Hrudey & Leiss 2003). However, the source of contamination that causes waterborne outbreaks of infectious disease is present wherever humans reside: human or animal fecal wastes. With this source of contamination, known to be capable of causing disease and death, always nearby, our practices to maintain the safety of our drinking water supply must be consistently rigorous.
Even with sophisticated management systems in place, water remains a very lowcost commodity. Failing to invest the relatively modest amounts that can achieve important improvements in safety is surely a false economy in an affluent society (Hrudey & Hrudey, 2002). The Walkerton Inquiry provided estimates of the costs for implementing all 93 recommendations of the Part 2 Inquiry report, which addressed the provision of safe drinking water for all of Ontario (O'Connor 2002b). These estimates identified an incremental cost (based on 10-year amortization of one-time costs) of between $7 and $19 per household per year. These are not onerous costs for assuring residents of Canada's wealthiest province that their drinking water is safe.
If our goal is to provide safe drinking water, we need to consider what is safe. First, let us consider what safe is not. Safe does not mean zero risk. There is no sharp line between safe and unsafe. Safe is not an absolute condition; it has meaning on a relative basis. Each person has a notion of safety that may vary from one risk to another. A pragmatic notion of safety is a level of risk so small that a reasonable, well-informed individual need not be concerned about it, nor find any rational basis to change his/her behaviour to avoid a negligible but nonzero risk. (Hrudey & Krewski, 1995).
In the context of drinking water, given our current capability for reducing risk, safe drinking water should mean that we do not expect to die or become seriously ill from drinking or using our tap water. Assuring that drinking water is essentially free (to negligible levels) from the risk of infectious disease can be and largely has been achieved for most public water supplies in affluent nations. The challenge is to maintain and extend that achievement as widely as possible. An equivalent pragmatic concept of safety was adopted by the Walkerton Inquiry (O'Connor, 2002b, p. 74).
The case studies reviewed for this book demonstrate that a zero risk of a waterborne outbreak can never be achieved; failures can happen in too many ways to assure zero risk. Humans inevitably make errors: there is little value in continuing to characterize failures as being caused by human error when we know that human errors are inevitable (Kletz, 2001). Rather, the focus must be on designing and maintaining systems that are able to preserve safe outcomes when human errors do occur.
No single action can be implemented to prevent outbreaks; there is no magic. Based on the cases presented here, we conclude that prevention can best be achieved by employing informed individuals committed to providing safe water. Hopefully, providing access to this compilation of the details from so many outbreak failures will equip committed people with a better appreciation of the range of things that can and do go wrong. In addition to raising awareness, these details should provide evidence of the need to take sensible actions when drinking water safety is at risk to convince those bottom-line-driven skeptics who may promote short-sighted false economies in the name of cost-saving or efficiency.
Converting hindsight into foresight is essentially an attempt to avoid having to learn painful lessons the hard way. By sharing the accounts of the problems and characteristics of these outbreak case studies, we hope to provide anyone who wishes to prevent drinking water outbreaks with a tangible sense of what can go wrong and why. If we can initiate and implement the conceptual equivalent of defensive driver training — learning how to avoid accidents without having to experience them — this book will achieve its primary objective.
CHAPTER 2
CAUSES OF WATERBORNE DISEASE OUTBREAKS
2.1 HISTORICAL BACKGROUND
Clean water has always been vitally important to human health and well-being, but the scientific understanding of how infectious disease can be spread by microscopic disease-causing agents (pathogens) in water has only been established over the past 150 years. The history of the understanding of water's role in disease transmission is rich, fascinating and complex. By introducing a few key details of the pioneering discoveries, we hope to convey some of the broader themes that also recur among many of the case studies that form the heart of this book.
Dr. John Snow (Snow, 1849) was the first to publish a rigorous explanation of how cholera was spread by sewage-contaminated drinking water in England. Snow's work was only one of a long series of publications in the British health and medical literature (Smith, 2002) attempting to explain the causes and transmission mode of cholera, which first reached Britain in the fall of 1831 and caused more than 21,000 deaths the following year (Morris, 1976). The Lancet devoted 44 pages of its November 19, 1831 issue to this new scourge, concluding (Lancet, 1831; Smith, 2002): "We can only suppose the existence of a poison which progresses independently of the wind, of the soil, of all conditions of the air, and of the barrier of the sea; in short, one that makes mankind the chief agent for its dissemination."
The re-appearance of cholera in Britain in 1848 and then in America in 1849 caused a renewed interest in the causes of cholera epidemics, including an insightful analysis of the global patterns of cholera outbreaks (Dickson, 1849). In the British Isles, the epidemic began in Scotland in October 1848 and appeared in London in February 1849 (Snow, 2002). This proved to be the most devastating of all the 19thcentury outbreaks, registering more than 6,000 deaths in Scotland and more than 53,000 deaths in England and Wales and accounting for more than 12% of all deaths in 1849 (Morris, 1976). According to the Surgeon-General's Catalogue, these recurring disasters led 777 individual writings on the subject of cholera to be published in London between 1845 and 1856 (Pelling, 1978).
Snow's first comprehensive explanation of his analyses of the causes of cholera (Snow, 1849), if somewhat premature by his own admission, was followed into print within a month by a monograph on the same subject from physician William Budd of the Bristol Infirmary (Budd, 1849; Smith, 2002). Budd concluded:
1. That the cause of malignant cholera is a living organism of distinct species.
2. That this organism — in shapes hereafter to be described — is taken by the act of swallowing into the intestinal canal, and there becomes infinitely multiplied by the self-propagation, which is characteristic of living beings.
3. That the presence and propagation of these organisms in the intestinal canal, and the action they exert, are the cause of the peculiar flux which is characteristic of malignant cholera; and which, taken with its consequences, immediate and remote, constitutes the disease.
4. That the new organisms are developed only in the human intestine.
5. That these organisms are disseminated through society, (1) in the air, in the form of impalpable particles; (2) in contact with articles of food; and (3) and principally, in the drinking-water of infected places.
Budd did acknowledge the "ingenious" and prior findings of Snow in his own work, but he concluded that Snow had failed to identify the agent of cholera, having identified only the drinking water vehicle, on which he agreed with Snow (Smith 2002). Snow in turn cited the work of Budd, disagreeing mainly with Budd's attribution of airborne transmission as offering even a secondary transmission route. However, Snow was concerned that he be credited with priority for the discovery of the waterborne theory so he exerted some effort to ensure this view of history prevailed (Snow, 1856; Smith, 2002).
Budd, although less well-known than Snow, was no less prolific in writing about the causes of waterborne disease. In particular, he wrote extensively in the Lancet (Budd, 1856) and the British Medical Journal about the waterborne cause of typhoid fever, a disease that was to exert a more pervasive fatal impact on industrialized countries in Europe and North America well into the 1900s.
After the 1848 and 1849 outbreaks, others investigating cholera for public health authorities contributed important evidence that was included in a report of the General Board of Health (Chadwick & Smith, 1850; Smith, 2002). Notably, Dr. John Sutherland, an inspector for the Board, working for the famous public health and sanitation advocate, Sir Edwin Chadwick, studied an epidemic associated with contaminated pump water in Salford (Sutherland, 1850). Sutherland's investigative report included a number of insightful comments from residents, including "he was afraid of using the pump-water, on account of the water in which the bedding of two persons who had died of cholera had been washed having been thrown into the gutter and he thought it ran into the well."
Sutherland observed in relation to these local concerns that "It appears that the well had been repaired, and from some cause or other, a sewer which passes within 9 inches of the edge of it had become obstructed and leaked into the well." Sutherland concluded that there was a remarkably strong association between household water and cholera, and that with respect to water from wells contaminated by sewage that the "predisposition occasioned by the continued use of such water is perhaps the most fatal of all." Although Sutherland held allegiance to the dominant theory that cholera was spread by "miasma" associated with filth and bad odour — a view strongly held by Chadwick — Sutherland's 1850 report was actually closer to the view espoused by Snow and Budd.
Despite the obvious connections among cholera, fecal waste disposal and drinking water contamination, Sutherland's chief point of disagreement with Snow and Budd was the interpretation of water being some kind of "predisposing factor" for cholera (Sutherland) rather than being the physical vehicle for transmitting the disease-causing agent (Snow and Budd). These have come to be characterized as the "miasma" versus the "contagion" theories. Although they disagreed strenuously at the time, both sides to this debate apprehended elements of the true causal mechanisms. That is, upon exposure to and infection with the agent responsible for cholera, the causal agent proliferated in the intestinal tract of cholera victims and subsequently contaminated drinking water through the fecal discharge in the profuse, watery diarrhea characteristic of cholera.
Others were drawing conclusions about a role for water, including John Lea in the U.S. who had concluded that use of rain water or boiled water protected against cholera (Smith, 2002). He communicated these views to the British government (Lea, 1851) and applied his theories to gathering rudimentary epidemiologic evidence for a cholera outbreak in Cincinnati in 1849 and reviewing an investigation by S.O. Butler of a similar investigation in St. Louis the same year (Smith, 2002). However, Lea incorrectly believed that the mineral content of water determined its "predisposition" to cholera.
The 1854 cholera outbreak in London allowed Snow to extend his initial monograph with a second, greatly expanded edition that reported on two compelling new investigations (Snow, 1855). The first investigation is, perhaps, the most commonly cited contribution from Snow, focusing on the explosive cholera outbreak that occurred in the Soho district of central London in early September 1854 (Snow, 2002). He described "the most terrible outbreak of cholera which ever occurred in this kingdom." The outbreak claimed over 500 lives in only 10 days and was ultimately linked to the water supplied by the Broad Street pump, now immortalized by a monument near the John Snow pub in Soho. This happened in an area less than 10 minutes walk from his home in Picadilly. Snow undertook an analysis of the cholera deaths during the week ending September 2 and, following detailed enquiries about the source of drinking water for each case, concluded that 83% of the victims had routinely consumed water from the Broad Street pump. Snow addressed the Board of Guardians of St. James parish on September 7 with his evidence and convinced them to remove the pump handle on September 8 (Snow, 2002). The relationship of this powerfully symbolic action to the course of the cholera outbreak (Figure 2.1), based on Snow's own data reporting date of onset, shows that the outbreak was largely over by the time the pump handle was removed. The decline in cases before September 8 may have been attributable primarily to the rate at which fearful residents abandoned the cholera-stricken neighbourhood.
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Excerpted from "Safe Drinking Water"
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