Article pubs.acs.org/est
Cluster Randomized Controlled Trial of the Plastic BioSand Water Filter in Cambodia C. E. Stauber,*,† E. R. Printy,‡ F. A. McCarty,† K. R. Liang,‡ and M. D. Sobsey‡ †
Institute of Public Health, Georgia State University, P.O. Box 3995, Atlanta, Georgia 30302-3995, United States Department of Environmental Sciences and Engineering, University of North Carolina−Chapel Hill, Campus Box 7431, Chapel Hill, North Carolina 27599-7431, United States
‡
ABSTRACT: About half of the rural population of Cambodia lacks access to improved water; an even higher percentage lacks access to latrines. More than 35,000 concrete BioSand Water filters (BSF) have been installed in the country. However, the concrete BSF takes time to produce and weighs hundreds of pounds. A plastic BSF has been developed but may not perform to the same benchmarks established by its predecessor. To evaluate plastic BSF performance and health impact, we performed a cluster randomized controlled trial in 13 communities including 189 households and 1147 participants in the Angk Snoul district of Kandal Province from May to December 2008. The results suggest that villages with plastic BSFs had significantly lower concentrations of E. coli in drinking water and lower diarrheal disease (incidence rate ratio 0.41, 95% confidence interval: 0.24−0.69) compared to control villages. As one of the first studies on the plastic BSF in Cambodia, these are important findings, especially in a setting where the concrete BSF has seen high rates of continued use years after installation. The study suggests the plastic BSF may play an important role in scaling up the distribution/implementation of the BSF, potentially improving water quality and health in the region.
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INTRODUCTION Worldwide, more than 884 million people still lack access to an improved source of drinking water and 2.6 billion lack access to improved sanitation.1 Household drinking water treatment (HWT) is an alternative and immediate approach to providing access to safe water to meet the needs of the staggering numbers who lack access. Studies of HWT have shown that it can greatly improve the microbiological quality of household drinking water and significantly reduce the risk of diarrheal disease on average by 35%.2,3 As a result there is a growing effort to identify technologies that can be scaled up to meet the needs of the population without access to improved water supplies.4 One promising technology is the Hydraid BioSand Water filter (BSF), originally invented by Dr. David Manz.5 The BSF is an adaptation of slow sand filtration to household scale. It is intermittently operated and can be housed in concrete or plastic. The version tested in this study is licensed by Dr. David Manz and manufactured by Cascade Engineering. The BSF, whether housed in plastic or concrete, has many advantages over other treatment technologies.6 These include a simple design and operation, durable materials, local fabrication of the media, and capacity to produce abundant quantities of drinkable water due to rapid BSF flow rates (∼ 0.8 L/min).6 Cohort studies in multiple locations have demonstrated reductions in diarrheal disease by the concrete BSF of 40% or greater.7−9 Recent evidence from Cambodia, Nicaragua, and the Dominican Republic also suggests high rates (>75%) of continued use after installation.9−11 Estimates suggest that worldwide >200 000 concrete BSFs have been installed; almost © 2011 American Chemical Society
a fifth of those installed in Cambodia between 2004 and 2007.4,12 The primary limitations of the concrete BSF are a slow rate of daily production and a weight of several hundred pounds. The latter makes it difficult to transport the concrete BSF to many remote locations where it is needed.4,13 Plastic BSFs may overcome these problems because the lightweight plastichousings can be mass-produced and nested for bulk transport. Plastic BSFs have a few key design differences, however, most notably a smaller pore volume to charge volume ratio. This ratio has been shown to impact microbiological efficacy in laboratory studies.14,15 In addition, the plastic housing is prone to a greater possibility of breakage. Taking these differences into account, we undertook three randomized trials of the plastic BSF in three countries: Cambodia, Ghana, and Honduras. The goal of the studies was to document the ability of the plastic BSF to improve water quality and reduce diarrheal disease in the field. Cambodia represents an important location to examine the plastic BSF because of high rates of adoption of concrete BSFs and a well-developed implementation program supported by Hagar Cambodia.9 The results presented here are one set of results from three similar trials of the plastic BSF that were conducted to evaluate health and microbiological impact in three very different settings. Received: Revised: Accepted: Published: 722
September 5, 2011 November 22, 2011 November 30, 2011 November 30, 2011 dx.doi.org/10.1021/es203114q | Environ. Sci. Technol. 2012, 46, 722−728
Environmental Science & Technology
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MATERIALS AND METHODS Ethics Statement. This study protocol was approved by the Institutional Review Board of the University of North Carolina and the Ministry of Health in Cambodia on 2/26/ 2008 (IRB 08-0063). Informed consent was obtained during the initial household visit from the primary respondent (defined as the primary caretaker for the children and responsible for household water management practices, usually an adult female). Research Setting, Study Population, and Participant Recruitment. This study, a cluster randomized controlled trial (CRCT) of the plastic BSF, was conducted in 13 rural communities in the Angk Snoul district of Kandal Province, Cambodia. Field data collection took place between March 13 and December 20, 2008. The Angk Snoul district of Kandal Province was selected for the following reasons: lack of access to piped water, absence of concrete BSFs, houses with children less than five years of age, no documented presence of arsenic in drinking water sources, and within reasonable daily transportation distance to Resource Development International-Cambodia (RDI-C). During initial recruitment, all villages in the district were approached. Village leaders were informed about the study including the intention to randomize the plastic BSF intervention at the village level, whereby about half the villages would be randomly selected to receive the plastic BSF about six months sooner than the other half of the villages. The village leaders were also informed they would not know into which group (plastic BSF or control) the village was selected until part way through the study. Once a village leader agreed that individual households in the village could be approached, all households in the village were approached. Households were excluded from the study only if they did not have a child less than five years of age and/or did not want to participate. Household recruitment began on March 13, 2008 and was finalized on April 10, 2008. The purpose of this initial phase of the study was to collect data on diarrheal disease prevalence in the households, and on potential risk factors of diarrheal disease including socio-economic status, age, education, knowledge about diarrheal disease, and access to water sources and sanitation. Data collection for the longitudinal prospective cohort began on April 21, 2008. Throughout the eight-month study, households were visited at two-week intervals and asked questions about diarrheal disease and water management practices in the home. Household drinking water was also sampled and analyzed at each visit. Intervention. The installation of plastic BSFs took place from July 9 to July 23, 2008. Prior to plastic BSF installation, numbers were assigned to each of the 13 villages. Then a list of numbers was randomly generated (from the range of numbers assigned). Those numbers that were selected (a total of 7) were assigned to receive the plastic BSF intervention resulting in seven intervention villages and six control villages. Health and hygiene education sessions were provided to all villages, including control villages, by Hagar Cambodia, the BSF implementing organization. All plastic BSFs were installed with an initial flow rate of 0.65−0.8 L per minute. If the flow rate was outside of the range, the plastic BSF was reinstalled. In the existing concrete BSF implementation program of Hagar, community members participate in the construction and installation of the concrete BSF and pay part of the concrete BSF cost in cash and sweat equity. To maintain fidelity to the
Hagar implementation program, each project household was asked to pay $10 for the plastic BSF. As a result, nine households in selected intervention villages did not receive the plastic BSF. They continued with the project and were later analyzed according to intention to treat analysis where they were included in the plastic BSF group observations. Diarrheal Disease Surveillance. Questionnaires were conducted approximately every 14 days. During the visit, the primary respondents were asked for a verbal report of any occurrence of diarrhea in the household within only the last 7 days of that 14 day period. If a person was identified as having diarrhea within the last seven days, it was considered a case of diarrheal disease as long as it met the World Health Organization definition (≥3 loose or watery stool in a 24 h period or any stool with blood). Field staff recorded all reports of diarrhea. If the case of diarrhea was identified during the interview, the following were asked of the respondent: date the illness began, duration, frequency of stool, and date illness ended. If it was ongoing, the interviewer asked questions to determine when the illness ended during the next visit. In addition to questions about diarrheal disease, the primary respondent was asked to confirm age of participants less than five years of age. Overall, there were five visits before plastic BSF installation and seven visits after, for a total of 12 nonconsecutive weeks of diarrheal disease observation. Plastic BSF installation for the entire project lasted approximately three weeks during July 2008 and no diarrheal disease surveillance was performed at that time. Water Quality Sampling and Analysis. Samples of drinking water were taken during household visits for both the control and plastic BSF groups. During the intervention phase, households with plastic BSFs provided three water samples at each visit (when available): prefiltered water, water directly from the plastic BSF outlet tube, and BSF treated water that had been stored for drinking. Control households provided samples of all water used for drinking which occasionally consisted of treated (often by boiling) water. Water samples were collected in 500-mL sterile bottles, stored on ice, and transported to the RDI-C laboratory, where they were immediately processed. All samples were tested for total coliforms and E. coli using membrane filtration onto BioRad’s Rapid’E. coli 2 agar (BioRad Laboratories, Hercules, CA). Concentrations in colony forming units (CFU) were determined by summing the total colonies divided by the total volume filtered. Turbidity was tested using the Hach 2100P Portable Turbidimeter (Hach Company, Loveland CO), according to manufacturer’s instructions. Data Analysis. All data analysis was performed in Stata 10 SE (College Station, TX). For the cross-sectional data, an estimation of household wealth quintiles was made using principal components analysis (PCA) of household assets.16 For this study, PCA was used to evaluate and generate a household wealth score from the following assets: bicycle, cart, car, motorcycle, refrigerator, television, fan, cellular phone, floor construction materials, access to latrines, and access to improved water. Based on the results of the PCA (using principal component 1), households were classified into quintiles of wealth and compared between the control and plastic BSF groups. The effect of the plastic BSF on diarrheal disease was assessed using Poisson regression to analyze incidence rates of diarrheal disease in the plastic BSF and control groups. The main exposure for the analysis was being in a village that 723
dx.doi.org/10.1021/es203114q | Environ. Sci. Technol. 2012, 46, 722−728
Environmental Science & Technology
Article
Figure 1. Study recruitment, participation and follow-up of cluster randomized controlled trial of plastic BioSand Water Filter in Kandal Province Cambodia. Note: Weeks of observation possible refers to a multiplication of the number of participants by the number of weeks for sample collection.
have improved water quality will report fewer cases of diarrheal disease irrespective of their intervention status. For this analysis, the main exposure variable was the log10 mean concentration of E. coli or turbidity, averaged by participant exposure throughout the study. The main exposure variable was cases of diarrheal disease over the total person-time observed summed for each participant. A multilevel Poisson regression was used to adjust for clustering at the household and village level.
received plastic BSF (according to intention to treat) and the main outcome variable was total cases of diarrheal disease over the total person-weeks observed per person. To perform this analysis, all reported cases and person-weeks of observation were summed by individual participant and modeled with Poisson regression. Multilevel Poisson regression was used to adjust for clustering that might occur at the household and village level. In addition to incident cases of diarrheal disease, case duration was also compared for plastic BSF and control groups. Case duration was determined by subtracting the date the case (illness) began from the date the case (illness) ended. Water quality data were log10 transformed including concentration of E. coli and turbidity (NTU). The microbial and turbidity reductions achieved by the plastic BSF were calculated as log10 reductions: log10 reduction = log10 influent − log10 effluent. Stored water quality was determined by measuring all untreated water provided from household storage containers. For the purpose of this analysis, drinking water quality in plastic BSF households was analyzed by measurement of E. coli and turbidity from samples taken directly from the plastic BSF outlet tube and from stored, plastic BSF-treated water. For control households, drinking water quality was determined by measuring all water designated for drinking in the household (including untreated and some treated samples). Unpaired t tests were used to compare geometric mean E. coli concentrations and turbidity between groups. To address the possibility of bias that might occur during repeated visits and with a nonblinded trial, an assessment of the impact of water quality on diarrheal disease was performed. This assessment is based on the assumption that those who
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RESULTS Study Enrollment and Completion. A description of study enrollment and participation is provided in Figure 1. After initial enrollment and prior to plastic BSF intervention, three households left the study because they moved, leaving 189 households eligible. For the longitudinal study, there were 546 people in 90 households in the plastic BSF intervention villages and 601 people in 99 households in the control villages. Tables 1 and 2 show characteristics of the plastic BSF and control groups based on data collected during the initial crosssectional recruitment. Statistically, the two groups did not significantly differ in any of the following variables: average age of participants, number of male and female participants, or the proportion of people who had ever or were currently attending school. Plastic BSF and control group characteristics regarding water, sanitation, hygiene, and socio-economic status are presented in Table 2 for the household level. The groups were significantly different when compared on access to improved drinking water during the dry season (November to April) (p = 0.001).They were, however, not different for
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dx.doi.org/10.1021/es203114q | Environ. Sci. Technol. 2012, 46, 722−728
Environmental Science & Technology
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Table 1. Age (As of April 2008) and Sex of Participants in Cluster Randomized Controlled Trial of the Plastic BioSand Water Filter in Kandal Province, Cambodia 2008
age participants ≥ 5 years old participants 2−4 participants
