The OECD Observer
January 1999, No. 215

 

New Molecular Technologies for Safe Drinking Water
By Elettra Ronchi and Salomon Wald

 

Microbial pollutants of water are a major cause of health and eco-nomic problems. Progress is being made in the techniques used to identify the pollutants, but there are questions about the costs. They have to be answered if a crisis is to be averted.

Until recently, water issues were overshadowed by other environmental concerns, such as climate change. But now water and its related problems have moved to the front of international environmental and health policy agendas. According to the World Health Organization, a third of the world population suffers from diseases derived from contaminated drinking water. Every year about 13 million people die from waterborne infections; of these, 2 million are children. The majority of these deaths occur in developing countries. However, water-borne pathogens—the agents that cause disease—are a growing hazard and a major economic burden in OECD countries too. For example, in the United States about 900,000 cases of illnesses and 900 deaths occur every year as a result of microbial contamination of drinking water. The annual cost to the US of waterborne diseases is about $19 billion.

In 1993, a major outbreak of gastro-intestinal illness caused by Cryptosporidium, a parasite which is commonly found in cattle, was reported in Milwaukee, the largest city in the state of Wisconsin. The disease outbreak cost the Milwaukee community over $55 million. Some 400,000 residents were infected, and more than a hundred people died.

This dramatic event revealed the vulnerability of the US water systems and led to a report in 1996, Global Decline in Micro-biological Safety of Water: Call for Action by the American Academy for Microbiology.

The American Society for Microbiology (ASM), a different though related professional organisation, has now prepared a second expert report underpinning the first one (Call for action) with further data and forecasts, some of which are quite ominous. It says, for example, that more than 20% of the US groundwater systems are contaminated. This has significant implications, since more than 100 million Americans rely on groundwater as a source of drinking water.

The ASM report also highlights how many of the outbreaks are associated with pathogen contamination of municipal water systems that operate according to governmental norms. Could this mean that current methodologies might be inadequate to monitor water quality or to detect failures of treatment systems? Indeed, current technologies lack the precision and specificity to measure low levels of pathogens and many micro-organisms, particularly viruses and parasites, can escape detection.

Even more disconcerting are recent reports on the possible long-term effects of waterborne viral infections. Enteric viruses, such as Coxsackie B, appear to be associated with heart diseases, in particular myocarditis, an illness which affects the muscular wall. This could be extremely significant, given that most deaths in OECD countries are cardiovascular-related.

To add to the problem, the Environmental Protection Agency in the United States has recently published a list of likely new contaminants of drinking water (Drinking Water Contaminant Candidate List). The list includes among other pathogens, Helicobacter pylori, a bacteria that has recently been associated with chronic gastric diseases. The situation in the United States is mirrored by other OECD countries. Disease outbreaks have recently been reported in Australia, Japan and Western Europe.

 

Solutions and Goals

Today, the assessment of microbial quality of drinking water is based exclusively on culture techniques. Since these methods do not allow for the detection of specific water pathogens, ‘indicator’ bacteria showing the possible presence of pathogens are monitored.

Most pathogens in drinking water are generally faecal in origin. That means they can be found in human and animal wastes. Thus the coliform bacteria, which are always present in the digestive systems of humans and animals, are commonly used as indicators. They are simply an indication that the water supply is contaminated and that disease-causing bacteria may be present. The method offers a good margin of safety against most bacterial pathogens, but is not effective against some other bacteria, viruses and protozoan parasites. For example, the deadly E. coli O157 may be present even when faecal coliform measurements show negative. Furthermore, viruses and most protozoan parasites, such as Giardia and Cryptosporidium, are resistant to chlorination and filtration, which usually kill coliform bacteria. As a result, coliform bacteria cannot be accurate indicators in such cases, particularly in chlorinated waters.

Furthermore, the indicator method usually requires cultivation on nutrient media which makes it impossible to obtain a reliable result within less than one day. By the time the results are available, pathogens might have spread wide in the water distribution system. There is clearly a need to find new approaches to monitor the microbiological quality of water.

 

New Molecular Technologies

Thanks to rapid advances in biotechnological research in the last few years, a wide range of new methods, principally based on the detection of nucleic acid material and its amplification, is becoming available. They offer a novel, more sensitive and specific way of detecting micro-organisms. They can also identify organisms that would not be detected with current culture techniques and can be used to track new pathogenic entities, including variants of otherwise harmless micro-organisms.

To date there are countless reports on the application of these methods in bacteriology. For example, 16S-ribosomal RNA probes and antibodies tagged with fluorescent labels allow the direct microscopic detection of target organisms within hours. Similarly, designed gene probes help in the detection of specific nucleic acid sequences which signal the presence of a particular organism in the sample. Amplification methods, such as polymerase chain reaction (PCR), can then be used to increase sensitivity.

There are probably very few groups of micro-organisms that have not been located with these amplification techniques and indeed several test kits have already been commercialised. This offers some hope for isolating some pathogens. But there are some important technical bottlenecks to overcome before they can be used to assess water quality and the micro-biological safety of drinking water. At an OECD workshop at Interlaken (Switzerland) in July 19981 several steps for improvement were agreed: research would have to target micro-organisms at levels useful for risk management or investigation; micro-organisms would have to be recovered from large amounts of water and tests run within minutes or hours, or even in real time; researchers would have to discriminate between viable and non-viable micro-organisms and identify specific pathogens of public health concern. Importantly, the running cost of monitoring would have to be made as affordable as possible.

 

The Economics of Water

To be useful, any methodologies for assaying microbial water quality must fulfil the needs of public health and environmental regulators. They also have to be cost effective enough not to impose an unacceptable burden on water suppliers and consumers. While it is not a viable option to have populations exposed to infected drinking water, it would not be realistic to raise operational standards of drinking water stations without considering the full economic and environmental costs.

Today, in most OECD countries the adoption of safety standards, such as in pesticides control, has led to major capital investments. For example, England and Wales have invested over a billion pounds to comply with safety standards. But few reliable figures exist on the relative costs of conventional and new technologies, though some speculation may be made based on the history of biotechnology innovation.

Three issues of major economic significance have to be considered. First, the costs of new technologies are almost always highest at the beginning, and come down over time. In the case of new diagnostics, a cost factor is also the fact that first generation technologies can seldom replace standard technologies and are primarily utilised to complement them. The open question then is how long will it take for the costs to come down, and what will the time-lag be between first and better second generation technologies? In the case of outbreak investigation, where rapid and sensitive diagnosis is a decisive factor, there is every reason to assume that molecular methods will ultimately be more cost-effective.

Second, cost considerations must be the long-term economic price of not using a new technology. This ‘opportunity cost’ will no doubt be different for rich countries than for poor ones and each country will have to make its own assessment on this. For grave diseases, such as cholera, the opportunity cost will be much more evident than for less severe ones. And even where the costs of non-action might seem low, pointing against the outlay, extending the cost-benefit analysis over a longer period of time could dramatically change the outlook. The example that water-borne infections can lead to heart and gastric diseases suggests the long-term economic costs of not using the best detection methods, whatever their price, could be very high indeed.

The third and final issue relates to the ‘therapeutic gap’ between detection and prevention. That gap varies according to the disease and there are major economic implications when the gap is wide. In many cases, detection of diseases is moving ahead faster than our ability to prevent or cure them. However, perhaps more can be done, and faster, to prevent and cure water-borne infection than other diseases.

 

An International Response

The demand for new molecular technologies raises diverse issues of its own. Different countries have varied problems. Some have plenty of water and others a scarcity, requiring recycling. In many OECD countries, the proportion of the population that can be reasonably connected to a community or municipal water plant is approaching its practical economic limits. Several countries have done well in providing water to small communities, and the application of appropriate technology can bring further progress at reasonable cost. On the other hand, to meet quality objectives for drinking water in densely populated areas, it has become necessary to treat sewage water. Soon cities will probably have to treat urban stormwater and wet-water overflows of sewage as well.

Most developing countries and many small community water systems in OECD countries do not have the necessary sophisticated laboratory infrastructure to comply with safe drinking water requirements. The differences in conditions underscore current variations in acceptable levels of pathogens and the fact that the concept of tolerable risk varies from country to country. Even in the United States there is no uniform view and standards vary from state to state.

To date there are international agreements on legal limits for pathogens—as reflected by EU directives and the World Health Organization’s international quality and safety standards—but only nationally-agreed measurement protocols. Yet common surveillance tools for water-borne disease are needed to reduce risk. That means standardising methodologies and validating them, preferably on an international basis. A mechanism for sharing validated methods is required. And last, but by no means least, wider exchange of comparable information is crucial so that research can meet public health needs while taking management and economic realities fully into account.

 

OECD Bibliography

Sustainable Management of Water in Agriculture: Issues and Policies—The Athens Workshop, 1998 (http://www.oecd.org/scripts/publications/bookshop/redirect.asp?511998081P1)

Water Management: Performance and Challenges in OECD Countries, 1998 (http://www.oecd.org/scripts/publications/bookshop/redirect.asp?971998061P1)

Biotechnology for Water Use and Conservation: The Mexico 1996 Workshop, 1997. (http://www.oecd.org/scripts/publications/bookshop/redirect.asp?931997051P1)