This thesis assesses the potential public health significance of, sanitation quality and coverage by using microbiological indicator and secondary health outcome data. Sanitation was categorised using The Millennium Development Goal (MDG) definition of improved (private pit latrine with a slab or better) and unimproved (toilets connected to open, pit latrine without a slab, hanging toilet, shared toilets). A spot check of sanitation facilities was conducted in 460 target houses and 1,784 neighbouring houses. Faecal contamination of the household environment was assessed by looking for evidence of contamination with faecal coliforms on children’s hands and on ‘sentinel’ toys (standardised toy balls provided by the study). An analysis of secondary data was conducted on sanitation and reported diarrhoea among children <5 years of age that had been collected as part of an impact evaluation. Households with private improved sanitation had lower faecal coliform contamination than households with unimproved sanitation [difference in means: -0.31 log10 colony forming units (CFU)/toy ball; 95% CI: -0.61, -0.01]. Access to 100% private improved sanitation coverage in the neighbourhood was associated with a small but statistically insignificant difference in contamination of sentinel toys (difference in means: -0.09 log10 CFU/toy; 95% CI: -0.56, 0.38). Other household sanitary practices such as cleanliness of latrine, wastewater disposal and disposal of animal faeces were important and statistically significant (P value ≤0.06) determinants of household faecal contamination. Children from households with access to private improved sanitation had a similar prevalence of diarrhoea to those with unimproved sanitation (Prevalence Ratio [PR] =1.00; 95% CI: 0.89, 1.13). Children from households with appropriate solid waste disposal systems had lower prevalence of diarrhoea compared to those without (PR=0.78; 95% CI: 0.65, 0.95). 4 Improved sanitation infrastructure quality and coverage may have limited roles in preventing transmission of diarrhoea causing enteric pathogens in the study context in which diarrhoea is endemic. Although in this study, private use and cleanliness of latrine were associated reduction in faecal contamination, but these factors were not associated with reduced diarrhoea prevalence. This may be because, firstly data were collected from slightly different contexts and time, secondly indicator organisms are only weakly associated presence of enteric pathogens and thirdly the population in this study context may have developed some degree of immunity to common circulating pathogens. Findings from this observational studies presented in this thesis adds to the evidence base, which do not support the inclusion of shared facilities as improved. There may be other more important source of children’s exposure to enteric pathogens that onsite sanitation access cannot prevent. Other sanitation related factors like maintenance of sanitation facility, use by all household members including children and faecal sludge management should be considered while defining improved sanitation for international monitoring. We also need to increase research efforts to integrate sanitation, water quality, handwashing and nutritional interventions and to understand better ways to monitor the impact of these interventions.