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Linking epidemiology to arsenic mitigation in Bangladesh

Dr Tony Fletcher

There is sufficient evidence to warrant immediate and large scale implementation of mitigation strategies: evidence from both the many measurements indicating hazardous levels of arsenic in drinking water, and the substantial numbers of victims of arsenicosis (especially skin lesions) identified in some communities in Bangladesh. It is important too that these efforts are prioritised to alleviate the problem where it is, or could become, most severe, and this aspect is rather uncertain.

Epidemiological approaches have much to offer in making the alleviation of arsenic related disease in Bangladesh most effective, and I shall identify some of the relevant contributions. By "epidemiology" I refer to disciplines involved in understanding the causation of disease (which usually comprises many interacting factors), quantifying the spread of disease and evaluating both prevention and treatment. These would all appear to be relevant in addressing the arsenic problem. It is by its nature multi-disciplinary involving among others, collaborations between specialists with skills in clinical medicine, biology, exposure assessment, laboratory analysis, nutritional science, statistics and social science.

Epidemiological methods can be used to evaluate the effectiveness of each approach to mitigation by conducting surveys of exposure, uptake, health status and awareness, before and after the mitigation intervention. The future success of the mitigation strategy will benefit from identifying the most effective approaches. Careful design and quality control is necessary to ensure that these comparisons are credible. The numbers who need to be surveyed, depend on how many different circumstances are being assessed, with due allowance for sufficient numbers of samples or examinations in each area.

Epidemiological methods will allow a quantitative assessment of how risk is related to arsenic uptake as well as other factors, such as other water contaminants, nutritional intake, and general health status. This information, combined with nation-wide mapping of the patterns of arsenic contamination will assist in prioritising the mitigation programme. It will also allow the first good estimate of the extent of current illness attributable to arsenic. This is not just of academic interest as there is uncertainty about what level of arsenic may be judged as "safe" or if not safe, then in some sense "acceptable".

Characterising the dose response relationship will be an important practical goal of the epidemiology. For this careful diagnosis and detailed characterisation of patterns of water consumption, analysis of arsenic in the water, measurements of arsenic in the body, and other factors, especially nutritional, will all be required. Sufficient numbers of individuals with different exposure will need to included to achieve some precision at the different exposure levels, including the lower ones where the corresponding risk is lower.

Epidemiological methods can be used to predict and measure the medium to long term impact of exposure to date, particularly in for the incidence of cancers. Health impact estimation (using the results of studies in other countries) will also allow the quantification of the long term impact if exposure were allowed to continue. Establishment of a surveillance system, for example in the framework of rural primary care schemes, should allow improved prognosis arising from earlier diagnosis among the exposed population. Follow-up of the population through careful surveillance and follow-up of a population of known past exposure, will also provide a measure of true incidence to compare with predicted estimates.

Points discussed

Helping to answer some urgent questions

There is no need to delay mitigation pending epidemiological research, but the evolving mitigation programme should benefit from answers to the following questions:

1. What is the magnitude of the health impacts?
2. What are the future impacts?
3. Is the mitigation successful? What are the determinants of successful mitigation?
4. What level of exposure is hazardous?
5. Which clinical treatments work best?

To address these we need:

• In-depth baseline surveys of health status -

Providing prevalence of disease by range and severity of condition: Skin lesions, psychosocial effects, cardiovascular problems, diabetes, reproductive problems.

• Repeat surveys of health status -

To test impact of mitigation and impact of treatment, including any problems in changes of water supply. Will need short term and long term repeats.

• In-depth baseline surveys of exposure and uptake -

Providing data on patterns of exposure in relation to pattern of well contamination and consumption of contaminated food.

• Repeat surveys of exposure and uptake -

Essential for demonstrating effectiveness of mitigation.

• Dose-response analyses -

Linking the data on exposure to data on health status, the quantitative relationship between arsenic exposure and ill-health can be described. Essential to distinguish importance of water and food - Linked to national water surveys, the total health impact may be estimated. Depending on the shape of the relationship, it may be possible to identify a no-effect level - Taking into account age, sex, nutritional status etc, we can identify groups at higher risk.

• Socio-epidemiological surveys -

Epidemiology involves not just studying disease. Interviews and group discussions will be needed to check on the population awareness, stigma and long term sustainability of the mitigation, for example:

• Does the population appreciate the risks of both arsenic contaminated and dirty water?
• Are they aware of the precautionary options?
• Can they still afford access to clean water?
• Are patients with arsenicosis still subject to stigma?

This will give insight into different characteristics of the mitigation which may be more or less successful.

• Assessment of treatments -

For skin lesions, treatments (creams, dietary supplements) need to be given but also assessed by clinical trials.

• Prediction and assessment of long term impacts -

From the detailed population exposure profile, long term effects such as cancer can be predicted but extrapolations are uncertain. A follow up study, following a sample of exposed villages to identify future cases of cancer is recommended.