Human Health

The contamination of water supplies by the livestock industry results in thousands of bacterial infections in Canada each year (Statistics Canada, 1999). Within the last decade, 1100 to 1600 cases of Verocytotoxigenic E. coli infection were reported annually in Canada, with the majority of cases attributed to infection by E. coli O157:H7. Between 9800 and 14000 cases of Campylobacter spp. infection were reported in Canada from 1986 to 1998 (BGOSHU, 2000).

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 Case Study

The recent outbreak of gastroenteritis in Walkerton, Ontario provides a useful case study of the human health effects of water contamination microbial pathogens originating from animal manure. On May 19^th, 2000 the town of Walkerton, experienced the largest outbreak of waterborne, bacterial gastroenteritis by multiple pathogens in Canada to date (BGOSHU, 2000). This incident marks the first time E. coli O157:H7 has ever contaminated a treated municipal water supply in Canada (BGOSHU, 2000). Of the 4900 residents of Walkerton, 1346 people (or 30% of the total population) became sick with gastroenteritis, and 2300 people overall (including people from outside the town of Walkerton) became sick with gastroenteritis from consuming the bacterially contaminated water. Gastroenteritis is diagnosed by the presence of diarrhea, or bloody diarrhea. Stool specimens may be infected with E. coli or Campylobacter spp. and patients can develop hemolytic uremic syndrome (HUS).  One hundred and seventy four individuals tested had evidence of E. coli in stool samples, and 116 people had Campylobacter spp. in stool samples. Sixty-five people were admitted to hospital, 27 individuals developed HUS, and six people with HUS died.  A total of 1000 people sought treatment in hospital emergency wards (BGOSHU, 2000).

The health costs resulting from the Walkerton epidemic have not yet been determined. While we cannot quantify the health costs at this time, a citizens group has filed a civil class-action suit claiming a total damage of $300 million dollars. In the aftermath of the outbreak, three separate surveys found that people consuming Walkerton water were nearly 12 times more likely to develop gastroenteritis than people who did not consume Walkerton water (BGOSHU, 2000). By mid-September, it was estimated that the Walkerton tragedy had already cost Ontario taxpayers $20 million and the “big-ticket items have yet to come” (The Edmonton Journal, 2000). Other costs to Ontario taxpayers include 12.2 million dollars to increase the activity in the water-monitoring program (The Edmonton Journal, 2000).

There are many other non-quantifiable damages associated with the outbreak, ranging from psychological damages associated with fear of contamination to the disruptions of regular behavior. The impact of the Walkerton outbreak remains, as the loss of those who died continues to affect the survivors of Walkerton. An environmental simulation model of drainage patterns and rainfall events indicate that the microorganisms contaminating the water supply likely originated from animal manure from a small Walkerton cattle farm (BGOSHU, 2000). The outbreak followed heavy rains that are thought to have played a large role in transporting bacterial contaminants into the water supply (BGOSHU, 2000).

Although the case of water contamination in Walkerton was the result of cattle manure, it is possible that a similar scenario could arise due to contamination of water by hog manure. This is supported by case studies in North Carolina that have linked hog run-off to outbreaks of bacterial gastroenteritis. Furthermore, these studies present the possibility that the existence of large amounts of hog manure stored in lagoons or deposited onto land may possibly be a threat to health in Quebec if drinking (municipal or private) water becomes contaminated. To avoid outbreaks of the same magnitude in the future, and in light of the proposed increase in the size of the hog industry, it is essential that a risk assessment be done to protect all residents of Quebec. In the meantime, it is recommended that all water bodies located near hog farms and all private wells are checked frequently for signs of contamination and more frequently during and after heavy rains. Besides these intervention methods, preventative measures are also recommended to avoid having to investigate health costs and the cost of lives lost when these situations could be avoided.

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To date, however, it has been impossible to quantify the degree to which the Quebec population is exposed to environmental contaminants resulting from livestock production (Gingras et al., 2000).  This is largely due to the lack of infrastructure available in Quebec to monitor the pollution emitted by the agricultural sector and the links such pollution has to human health (Gingras et al., 2000).

Table 6: Water contamination surveillance system in Quebec.

Among the class of infections collectively known as "notifiable diseases", which are classified differently at the federal and provincial levels, are those transmitted by hogs to humans including Salmonella, Campylobacter, E. coli and Yersinia entercolitica.  The gastroenteritis infections caused by these microorganisms are generally linked to animal production and animal products, but not restricted to transmission by hogs alone. Professionals working in the field of public health feel that the list of “notifiable diseases” should be expanded to include other vectors, such as the parasite Cryptosporidium parvum, to provide a more extensive survey of infection (Millard, pers. comm., 2000).  This parasite, found in the feces of hog, cattle and other ruminants, causes profuse diarrhea, abdominal pain, nausea, vomiting, fatigue and fevers.  It was responsible for a massive outbreak in Milwaukee in 1993 where 400 000 people were infected through their water supply (MacKenzie et al., 1994).  Another hog vector that has recently been discovered to produce antibodies in humans is hog strain of hepatitis E (Gingras et al., 2000), which is not yet classified as a notifiable disease.

Nevertheless, if one of the notifiable diseases is found in a patient, reports are made to one of the 18 Direction de la Sante Publique (DSP) offices located in different regions of Quebec.  The DSP is responsible for identifying possible sources of infection and implementing measures to protect public health (Gingras et al., 2000). Possible sources of the infection are determined through a questionnaire. If all other possible sources of infection are eliminated, such as food contamination, the case is sent to the Ministry of the Environment to investigate the possibility of water contamination.

Individual cases of notifiable diseases are entered into a central provincial database (Gingras et. al., 2000).  However, the database does not contain information pertaining to exposure and risk factors that are often discovered from the DSP questionnaires nor does it distinguish between individual cases and outbreaks (Gingras et. al., 2000).  In January, a centralized registry of outbreaks, which includes information pertaining to possible sources and vectors of transmission, was developed to report and monitor outbreaks (Gingras et. al., 2000).  This will help to quantify the mortality and morbidity rates due to outbreaks in the future.

Even though approximately 20% of the Quebec population gets their water from private wells (Gingras et al., 2000), there is currently no legislation requiring systematic testing for contamination (Barthe, pers. comm., 2000).  In a survey of outbreaks between 1989 and 1995 (Table 7), several cases were related to private well contamination from microbial byproducts that were suspected to originate from animal production operations. Inadequate information in the database makes it impossible to state conclusively that human disease resulted from water contamination by animal production operations (Gingras et. al., 2000). 

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Table 7: Gastroenteritis outbreaks suspected of being linked to agricultural pollution by public health professionals in Quebec (1989 to 1995). Source: Bolduc and Chagnon (1996) [emphasis added].

The current system of surveillance is a passive, rather than an active one, which  make it impossible to accurately calculate the costs resulting from microbial infections from contaminated water at this time (Barthe, pers. comm., 2000).  As a result of this passivity and the general lack of funding required for further investigation, there is only a limited amount of documentation. Moreover, people may not seek medical attention if symptoms are relatively mild, and the appropriate tests required to identify the potential of microbial contamination may not always be performed  (Alors, pers. comm., 2000).  Furthermore, the DSP’s system of inquiry, namely the questionnaire, is not designed to make the links between agriculture, water and human health (Kasantsky, pers. comm., 2000).  This could be addressed by making changes to the questionnaire after consulting with health care professionals to ask appropriate questions (Kasantsky, pers. comm., 2000). 

In North Carolina, a public opinion survey was used in one study to determine the degree to which people's health is affected by living near to a hog farm (Wing and Wolf, 1999). A survey of 155 people found that the residents living in close proximity to hog farms reported increased occurrence of headaches, runny nose, sore throat, excessive coughing, diarrhea, and burning eyes than people in the community who resided farther away from livestock operations (Wing and Wolf, 1999).  Surveys could be used to quantify the effects of the hog industry on human health to document effects that are not reported to doctors or other health care professionals. Similar surveys have not been conducted in Quebec and should be considered as a method for further research into the effects of the hog industry on human health.

Provincial regulations for the surveillance of drinking water are only applicable to systems serving more than 50 people (Gingras et al., 2000).   However, water systems serving less than 5000 people are vulnerable to contamination due to an absence or inappropriate level of water treatment, the lack of mandatory training of managers of water systems, and the limited testing of water supplies (Gingras et al., 2000).

We investigated the cost of water-boiling notifications due to water contamination, which may or may not be linked to animal production. Quebec has the highest number of water-boiling notifications in Canada with approximately 600 notices per year (Hawaleshka, 2000).  In Montreal, the cost of one notification is approximately $5000 (Gagne, pers. comm., 2000).  Since Montreal is the largest city in Quebec, the cost of a notification of this sort would probably be less in smaller municipalities, so this number will only be used as a rough estimate. Accordingly, six hundred water-boiling notifications in Quebec cost approximately $3 000 000 each year.

An example of human health problems that may result from chemical byproducts of the hog industry is disease caused by consuming water with elevated nitrate concentrations.  However, there have been no recent reported cases in Canada of methemoglobinemia (blue baby syndrome), a disease that can be fatal to infants who consume water containing more than 10 ng of nitrate per liter (Gingras et al., 2000).  It is impossible to quantify the degree to which the population is affected by low level exposure to nitrates since low-level effects are hard to diagnose. Although nitrate consumption in adults has been linked to spontaneous abortions, non-Hodgkin's lymphoma and stomach cancer, the problem of causality and the lack of research in this area make it impossible to quantify the degree to which the population is affected (Gingras et al., 2000).