Health impact studies

The recent studies on the health impact of biosand filter use are encouraging. However, there is still a need for more studies in populations using the household intermittent biosand filter. The rationale for health impact studies cited below was outlined to biosandfilter.org by Dr Mark Sobsey, University of North Carolina.

The intermittent bio-sand filter has no health impact data to use for comparative analysis with other household based water treatment technologies. Health-based data are essential for these analyses, such as cost-effectiveness analysis. The critical “metric” for WHO and others who conduct these analyses and calculate the costs, benefits and other econometrics of international health interventions is health data. The WHO and others use the health impact measure of Disability Adjusted Life Years (DALYs), which can be calculated for any disease, including diarrhoea, gastroenteritis, cholera, etc. For example, using health impact data from reductions in household diarrhoeal disease from household water intervention studies, one can calculate DALYs and use this in the economic analysis to determine the unit reduction in disease burden relative to the cost of the intervention for a particular water treatment intervention.

The intermittent bio-sand filter is currently at a disadvantage for uptake and dissemination by major players because of the lack of health-based evidence for its performance. We lack both fundamental data on how well the bio-sand filter removes pathogens and how well it reduces household waterborne disease. Just because the intermittent bio-sand filter may be pretty good at reducing faecal coliform bacteria does not mean it will be good as reducing other classes of pathogens, such as viruses. Therefore, we are as yet unable to make a scientifically valid, health-based assessment of its performance as a water treatment system that is intended to remove contaminants from water that cause disease, especially waterborne pathogens. However, research into the performance of the intermittent filter to remove differing pathogenic organisms is currently ongoing – click here for more details.

Despite the limited evidence of the bio-sand filter to reduce faecal indicator bacteria, it is impossible to make a scientifically valid analysis of its performance in health impact for reducing disease burden within the analytical framework that exists and is globally used for these decisions. This is especially true for the bio-sand filter because is not a standard and well characterized water treatment technology. It is not a standard slow sand filter because it is not designed and operated according to standard slow sand filter protocols. Among other things, the flow rate is higher, the intermittent application of water and variable head is contrary to how continually-operated slow sand filters are operated, and the use of sand of variable specifications (origin, size range, mineralogy), is not consistent with standard slow sand filter criteria. For example, current work in Dr Sobsey’s laboratory shows that even turbidity removal in an intermittent bio-sand filter will vary quite a bit with the volume and frequency of intermittent water application. In contrast, turbidity removal in standard continually-operated sand filters tends to be quite stable and consistent through a filter run.

Therefore, there is no scientifically valid basis for assuming the intermittent filter will reduce pathogens and reduce waterborne disease risk as would a standard continually-operated sand filter. The health-based analytical framework using DALYs is central to the work of WHO and other international health decision-makes about what to invest in to improve global health and reduce the global burden of disease. If one wants a technology or intervention such as the intermittent filter to be an option that will be considered along with other options, decisions makers will want to see the health-impact based economic analysis.

Research is needed to assess the health impact of a bio-sand filter project. What is needed is to be able to measure household diarrhoeal disease before and after the intervention, in order to calculate DALYs, which can then be used for health-impact based economic analysis.