Thermotolerant coliforms in drinking water as predictors of diarrhea: An analysis of combined data from multiple studies Open Access

Hodge, James Michael (2015)

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Background: Inadequate access to microbiologically safe water continues to be a driver of the global burden of diarrheal disease. Interventions to improve water quality have been shown to be effective at both improving the microbiological safety of drinking water as well as reducing risk of diarrhea. When evaluating water quality, thermotolerant coliform (TTC) bacteria indicative of fecal contamination are frequently used due to the infeasibility of pathogen-specific tests. However, the association between the quantity of TTC in drinking water and health outcomes is not well defined. This study aims to address this knowledge gap and provide further evidence as to whether improving drinking water quality impacts the risk of diarrhea.

Methods: Individual level data was obtained from seven previous studies that collected data on water quality based on TTC/100ml and self-reported diarrhea over a seven-day recall period. Data was combined into one data set and analyzed using multilevel logistic regression models with diarrhea as a binary outcome variable and TTC/100ml as the predictor variable. Odds ratios were calculated for TTC as a continuous variable to evaluate whether increases in TTC/100ml are associated with an increased risk of diarrhea and as a categorical variable to evaluate whether there is evidence of a dose-response or threshold effect.

Findings: For the combined data set there is a statistically significant association between TTC/100ml and diarrheal disease for all ages (OR:1.12; 95% CI:1.08-1.18) and for children under five (OR:1.18; 95% CI:1.11-1.26). There was also evidence of both a threshold effect at 10 TTC/100ml when compared to <1 TTC/100ml and a dose-response effect. Odds ratios followed a significant increasing linear trend (p<0.001) as the exposure categories increased.

Conclusions: This study found evidence of a significant association between TTC and diarrheal disease as well as significant dose-response and threshold effect. These results challenge recent studies and provide support for health-based WHO guidelines that limit TTC levels in drinking water. Furthermore, the association between fecal contamination and risk of diarrhea found here provides further support to suggest that improving drinking water quality is an important method of reducing the global burden of diarrheal disease.

Table of Contents

Section 1: Introduction and Rationale 1

Section 2 Literature Review 6

Global burden of diarrheal disease 6

Inadequate access to safe water 7

Indicator bacteria 11

Indicator bacteria and diarrheal disease 12

Section 3: Methods 18

Included studies 18

Methods for assessing diarrhea and water quality 19

Data extraction and synthesis 20

Statistical Analysis 21

Sensitivity Analysis 22

Ethics 22

Section 4. Results 22

Diarrhea prevalence 23

Water quality 24

TTC-Diarrhea assessment 24

Threshold effect and dose-response assessment 25

Sensitivity analysis 25

Section 5. Discussion 26

Section 6: Conclusion and Recommendations 30

Acknowledgements 32

References 33

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