Data source
The study used data from the WHO Study on Global AGEing and adult health (SAGE). Wave 2 was a survey conducted in six LMICs, including China, Ghana, India, Mexico, Russian Federation, and South Africa17. The nationally representative survey collects data through a stratified multistage cluster design to complement existing ageing data sources and inform policy and programmes. WHO and the University of Ghana Medical School through the Department of Community Health collaborated to implement SAGE Wave 2 in Ghana in 2014–2015. We used the GhanaINDDataW2 and GhanaHHDataW2 datasets. The INDD data set comprised of individual questions targeted at the main respondent and the HHD data set comprised of questions concerning the household within which the primary respondent resided.
The primary sampling units were stratified by region and location of residence (urban/rural) with samples selected from 250 enumeration areas13. In households identified as “older” for sampling purposes, all household members aged 50 years and older were invited to participate in the study. Individuals were interviewed regarding their chronic health conditions and health services coverage; subjective wellbeing and quality of life; health care utilization; risk factors and preventive health behaviors; perceived health status; socio-demographic and work history; social cohesion, and household characteristics. Respondents further provided details about the use of water and sanitation facilities, including the source of water and type of toilet facility and whether these facilities were shared with others. Primary data management, checking and quality assurance was undertaken by country survey teams and coordinated centrally through WHO Geneva. The Ghana response rate was 83%. The data are publicly available via the WHO Multi-Countries Study Data Archive. Details on data and further information can be found at http://www.who.int/healthinfo/sage/cohorts/en/. Weight was calculated to offset the sampling effect.18
Measures
Outcome variable
The main outcome variable of interest in this study was occurrence of chronic conditions defined as the existence of one or more chronic conditions on an individual (ranging from 1 to 8). We included all available self-reported chronic conditions queried in the WHO-SAGE data, each prompted by the item “Has a health care professional ever told you that you have… hypertension, diabetes, chronic lung diseases, angina, asthma, tightness in the chest, stroke, and arthritis?”. Individuals who indicated “yes” to these items were recorded as having a chronic condition. We dichotomized the outcome variable into 0 = no chronic condition when the respondent answers “no” to all the items and 1 = occurrence of chronic conditions when at least one response was affirmative (1-8).
Explanatory variables
Three independent variables were considered in this analysis: the source of water, type of toilet facility and shared toilet facility. First, older adults were asked to indicate the main sources of drinking water. The responses were broadly categorized into 1= piped private, 2= piped to yard/plot, 3= public tap/standpipe, 4= tube well/borehole, 5= protected dug well, 6= unprotected dug well, 7= protected spring, 8= unprotected spring, 9= rainwater collection, 10= bottled water, 11= small scale vendor, 12= tanker-truck/lorry, 13= surface water (river, lake, etc.).
Based on the Joint Monitoring Program’s classification of water and sanitation technologies1, we recoded these sources of water into “improved source” =1 to include piped private, piped to yard/plot, public tap/standpipe, tube well/borehole, protected dug well, protected spring, bottled water, small scale vendor, tanker-truck/lorry, and “unimproved source” =2 to include unprotected dug well, unprotected spring, and surface water. Type of toilet facility was collected on a 12-response scale including 1= flush/pour to piped sewage system, 2= flush/pour to septic tank, 3 = flush/pour to pit latrine, 4= flush/pour to other locations, 5= flush/pour to unknown, 6= ventilation improved pit latrine, 7= pit with slab, 8= pit without slab/open, 9= composting toilet, 10= bucket, 11= hanging toilet/latrine, 12= no facilities (bush, field).
These responses were transformed into 1= “improved toilet facility” (flush/pour to piped sewage system, flush/pour to septic tank, flush/pour to pit latrine, flush/pour to other locations, flush/pour to unknown, ventilation improved pit latrine, pit with slab, composting toilet), and 2= “unimproved toilet facility” (pit without slab/open, bucket, hanging toilet/latrine, no facilities (bush, field). Finally, participants answered on a “no” =1 or “yes” =2 scale about whether toilet facility was shared with others.
Covariates
Sociodemographic and health-related variables were assessed and included for adjustments. These included age (years), gender (1= male, 2= female), location of residence (1= urban, 2= rural), and years of education. Marital status was collected using a four-level measure but collapsed and dichotomized into currently married/partnered =1, and not currently married/partnered = 2. WHO-SAGE collected data on ethnic background on a 10-level scale but the variable was dichotomized into 1= Akan, 2= others due to the limited frequencies for specific categories and subsequent incidence of model over-fitting in the regression analysis. Respondents were asked to rate their own health, on a scale from 1 to 5 (very good, good, moderate, bad, very bad) with the item, “how would you rate your current health state?” A higher score indicated poor self-rated health and we recoded this variable into good (very good, good) =1, moderate =2 , bad (bad/very bad) =3 for analytic purposes.
Statistical analysis
Univariate descriptive analysis was first conducted to generally describe the characteristics of the sample. These statistics were reported as mean and standard deviation for continuous variables, or count and percentage for categorical variables. Next, we performed bivariate analysis stratified by gender and location of residence to estimate the relationships between the study variables using non-parametric Pearson’s χ2 test for categorical variables and independent t-test for continuous variables. Kendall’s tau-b correlations were run to determine the relationships of relevant exposure variables with the outcome variable. Accounting for the complex survey design, survey weights were used to estimate gender- and residential-specific prevalence of chronic conditions, and water and sanitation indicators.
Given the measurement level of the outcome variable, series of hierarchical generalized logistic regression models were conducted in which the occurrence of chronic condition was regressed on the major independent variables (water, and sanitation) controlling for the potential confounders. Models 1, 2 and 3 regressed chronic condition occurrence on water source, toilet facility type and sharing of the toilet facility respectively. These crude models estimated the variance explained by the three key independent variables. In addition, chronic condition occurrence was regressed on the three key independent variables simultaneously in Model 4. Model 5 added the sociodemographic and health-related variables as controls. In Model 6, we included the interaction terms (water/sanitation indicators × gender and water/sanitation indicators × residential status) to investigate the potential modifying roles of gender and location of residence in the association of water, sanitation and chronic condition occurrence. In a confirmatory analysis, we fitted separate models to estimate the specific effect of independent variables on each individual chronic conditions. We checked for multicollinearity by computing the Variance Inflation Factor (VIF) but none of the VIF scores exceeded the value of 2.5, indicating no multicollinearity. A p-value of less than 0.05 was considered statistically significant and all analyses were performed using SPSS v.21.0 (IBM, Armonk, NY).