Abstract
Poor household drinking water quality and the early childhood diarrhea (ECD) and child growth stunting that result from it are a scourge that leads to the premature death of nearly 1.6 million children worldwide each year. Researchers have long studied the causes and prevention strategies of poor household water quality and ECD using intervention-control trials. Although the results of such trials can lead to useful information, they do not capture the complexity of this human/engineered/natural system. This dissertation reports on the development of an agent-based model (ABM) to study such a system in Limpopo, South Africa. This method proved to be an effective tool to develop a robust, quantitative understanding of the complex coliform bacteria transmission chain that leads to ECD and to investigate key mechanisms, risk factors, behaviors and intervention strategies to mitigate such transmission. This was achieved in three main parts. The first was an investigation of the sources and regrowth mechanisms of coliform bacteria as well as water, sanitation and hygiene (WASH) behavior in the communities. The second part was to use that information to inform the development of an ABM and use that ABM to explore the various risk factors affecting the outcome variables of household water quality, ECD incidences and child growth stunting. Lastly, the ABM was used understand the long-term sustainability of a ceramic water filter (CWF) campaign using field data about longitudinal
microbial effectiveness.
In addition to these three main studies related to the ABM, data from a fourth study was analyzed which investigated the possible use of a silver-infused torus which has the potential to reduce biological contamination and regrowth in the lower reservoir of CWFs and compared the long-term effectiveness of such filters to point-of-use (POU) chlorination and CWFs without the toruses.
The first studied related to the ABM comprehensively investigated contamination sources and the biological and chemical mechanisms sustaining them in two adjacent communities in rural Limpopo, South Africa. The eight month study was conducted of household and source water quality measurements, measurements of biofilm layers on the inside of household water storage containers and water transfer devices, and measurements of hand-based coliforms and hand-washing effectiveness. A 7-day water
container incubation experiment was also performed to determine the biological and chemical changes that occur in a household water storage container independent of human interference. Results indicate that household drinking water frequently becomes contaminated after collection but before consumption (197 vs 1046 CFU/100 mL, n = 266, p < 0.001). The most important contamination sources include biofilm layers on the inside of storage containers (1979 CFU/100mL), hands (1041 CFU/100 mL) and coliform regrowth resulting from high assimilable organic carbon (AOC) levels during storage. A maximum specific growth rate, μmax, of 0.072 h 1 was measured for total coliform bacteria on AOC and a high correlation between AOC concentrations and the growth potential of total coliform bacteria was observed. These results support the implementation of point-of-use water treatment and other interventions aimed at maintaining the safe water chain and preventing biological regrowth.
The second study captured the essential WASH elements of the communities and their water contamination chain as identified in the first study to construct the ABM. An extensive analysis of those elements explored behaviors including water collection and treatment frequency as well as biofilm buildup in water storage containers, source water quality, and water container types. Results indicate that interventions must be optimally implemented in order to see significant reductions in ECD. Household boiling frequency, source water quality, water container type and the biofilm layer contribution were deemed to have significant impacts on ECD. Furthermore, concurrently implemented highly effective interventions were shown to reduce diarrhea rates
to very low levels even when other, less important practices were sub-optimal. This technique can be used by a variety of stakeholders when designing interventions to reduce ECD incidences in similar settings.
The third study used the ABM to investigate CWFs. CWFs are a point-of-use water treatment technology that has shown promise in preventing ECD in resource limited settings. Despite this promise, some researchers have questioned their ability to reduce ECD incidences over the long term since most effectiveness trials conducted to date suffer from lack of blinding and are thus potentially biased. This study uses the ABM to explore factors related to the long-term sustainability of CWFs in preventing ECD and was based on a three year longitudinal study of microbial effectiveness, usage and willingness-to-pay (WTP) for replacement filters. Specifically, filter prevalence, usage, breakage rates and dates, microbial effectiveness, filter cleaning and linear
usage declines were explored. There were additional investigations about WTP for new filters and user perceptions of water quality. This study demonstrated the ability and flexibility of the ABM to simulate interventions. Results indicate that human behaviors are the primary driver of the outcome metrics and that deteriorating filter effectiveness has a significantly negative role on those same outcome metrics. In fact, microbial effectiveness declines to such an extent as to make the CWFs practically useless, on average, at preventing ECD after 3 years. Overall, the model predicts that a ceramic filter intervention can reduce ECD incidence by 41.3%. The three most important factors included CWF usage, prevalence and linear usage declines. It was also shown that CWF log reduction values less than 3 resulted in sub-optimal outcomes and that users should clean their filter at least once every six months to improve outcomes. Finally, this study showed that outcome variables could be
improved somewhat if replacement filters were available for 100 South African Rand or less and if community members recognize and treat their water more frequently when water quality is worse than 10 CFU/100mL of total coliform bacteria. In summary, the CWF can be a highly effective tool in the fight against ECD, but every effort should be made by implementing agencies to ensure consistent use and cleaning.
The fourth study concurrently compared three different POU technologies including POU chlorination, CWFs and CWFs plus lower reservoir toruses to prevent biological contamination and regrowth. These results indicate that all three technologies decline in microbial removal efficiency over time, but there is no clear difference between the three technologies. The relative equity was likely caused by the fact that the torus, as designed, was unable to maintain silver concentrations in the lower reservoir water at levels significantly higher than CWFs without the toruses. Furthermore, although chlorination did prove to be effective at reducing total coliform and E. coli levels, it suffered from poor adherence. These results are consistent with the other studies reported on in this dissertation in that they highlight the relative importance of compliance and human behaviors as playing a large role in ECD reduction.
The three ABM studies demonstrate the usefulness of systems approaches to investigate the complex coliform transmission chain from source to consumption and to identify risk factors and behaviors that can mitigate the scourge of contaminated water leading to ECD in resource-limited settings. The fourth study adds to it by re-emphasizing the importance of human behaviors in ECD prevention. Collectively, this dissertation has attempted to develop a robust, quantitative understanding of the complex coliform bacteria transmission chain that leads to ECD and it investigates key mechanisms, risk factors, behaviors and intervention strategies to mitigate such transmission.
