Choice of controls for a case-control study in Bangladesh: Hospital controls versus community controls

The study aimed to determine whether hospital controls could be used in case-control studies with minimal bias, where resource constraints limit recruitment of community controls. Hospital controls and community controls were compared for socio-demographic and risk factor variables in a study of Smokeless Tobacco (SLT) use and Coronary Heart Disease (CHD) in Bangladesh in 2010. Incident cases of CHD and hospital controls were selected from cardiac hospitals. Community controls were selected from neighbourhoods of CHD cases. We enrolled 302 cases, 302 hospital controls, and 1208 community controls. Distribution of age, gender, marital status, occupation, and socio-economic status was similar between hospital controls and community controls. Compared to community controls, hospital controls were more educated, had higher rates of hypertension and reported more family history of heart diseases. But they reported relatively less physical activity. Current use of SLT was higher amongst community controls compared to hospital controls, but was not significant (adjusted OR 0.81, 95% CI 0.58-1.12). Current use of SLT was not associated with an increased risk of CHD when community controls were used (adjusted OR 0.87, 95% CI 0.63 to 1.19, p>0.05), nor when hospital controls were used (adjusted OR 1.00, 95% CI 0.63 to 1.60, p>0.05). There were significant differences between two control groups but only on confounding variables which could be measured and adjusted for during multivariate analyses. For comparable future studies in resource-scarce settings, it is possible to enrol hospital controls with careful planning which are similar to potential community controls, whilst minimising selection bias.