Private health care market shaping and changes in inequities in childhood diarrhoea treatment coverage: evidence from the analysis of baseline and endline surveys of an ORS and zinc scale-up program in Nigeria

Background Nearly 90,000 under-five children die from diarrhoea annually in Nigeria. Over 90% of the deaths can be prevented with oral rehydration salt (ORS) and zinc treatment but coverage nationally was less than 34% for ORS and 3% for zinc with wide inequities. A program was implemented in eight states to address critical barriers to the optimal functioning of the health care market to deliver these treatments. In this study, we examine changes in the inequities of coverage of ORS and zinc over the intervention period. Methods Baseline and endline household surveys were used to measure ORS and zinc coverage and household assets. Principal component analysis was used to construct wealth quintiles. We used multi-level logistic regression models to estimate predictive coverage of ORS and zinc by wealth and urbanicity at each survey period. Simple measures of disparity and concentration indices and curves were used to evaluate changes in ORS and zinc coverage inequities. Results At baseline, 28% (95% CI: 22–35%) of children with diarrhoea from the poorest wealth quintile received ORS compared to 50% (95% CI: 52–58%) from the richest. This inequality reduced at endline as ORS coverage increased by 21%-points (P <  0.001) for the poorest and 17%-points (P <  0.001) for the richest. Zinc coverage increased significantly for both quintiles at endline from an equally low baseline coverage level. Consistent with the findings of the pairwise comparison of the poorest and the richest, the summary measure of disparity across all wealth quintiles showed a narrowing of inequities from baseline to endline. Concentration curves shifted towards equality for both treatments, concentration indices declined from 0.1012 to 0.0480 for ORS and from 0.2640 to 0.0567 for zinc. Disparities in ORS and zinc coverage between rural and urban at both time points was insignificant except that the use of zinc in the rural at endline was significantly higher at 38% (95%CI: 35–41%) compared to 29% (95%CI, 25–33%) in the urban. Conclusion The results show a pro-rural improvement in coverage and a reduction in coverage inequities across wealth quintiles from baseline to endline. This gives an indication that initiatives focused on shaping healthcare market systems may be effective in reducing health coverage gaps without detracting from equity as a health policy objective.