Our modeled maps show substantial local variation in both the incidence of diarrhea and diarrhea-related mortality among children younger than 5 years of age in Africa over the period from 2000 to 2015. The rates of decline in incidence and mortality varied both among countries and within countries at every level of spatial aggregation that we considered. Some countries appeared to have substantially reduced their diarrhea burden uniformly, whereas others were behind on their progress countrywide. In addition, the higher-resolution subnational estimates identified a third group of countries in which progress varied subnationally. By providing estimates of current rates and counts of severe incidence and mortality, we identified locations that are most in need of interventions to reduce diarrhea burden.

More than half the diarrhea-related deaths in Africa were estimated to occur in 7% of the first-level administrative subdivisions, which encompass 35% of the population in Africa. These highly populated locations with high mortality rates — many of which are in Nigeria, Ethiopia, and Niger — are places where targeted interventions to reduce mortality, even modestly, could avert many deaths. Conversely, in-depth evaluation of the factors that have contributed to success in countries such as Ethiopia, where the case fatality rate declined by more than 60% from 2000 to 2015, could reveal important strategies for reducing the case fatality rate in other areas. As noted by Troeger and colleagues (on behalf of the GBD Diarrhoeal Diseases Collaborators),1 Ethiopia has had considerable improvements in child nutrition over the 2000–2015 period. Such improvements, combined with an expanded use of oral rehydration therapy, appears to account for much of the reduction in mortality in that country.1

The relative intractability of diarrhea incidence, as compared with diarrhea-related mortality, as shown in the present analysis and elsewhere,1 may suggest that growing access to timely and appropriate treatment, better nutritional status, and fewer coexisting conditions are contributing factors to reducing diarrhea-related mortality. A variety of interventions — including programs to promote immunization, hygiene, breast-feeding, oral rehydration therapy, and zinc supplementation — have been used effectively on a small scale to combat diarrheal disease and death.1,31 Targeting the locations with the highest estimated case fatality rates, such as those in Lesotho and Mali, is likely to have a larger effect than untargeted approaches. Although the introduction of the rotavirus vaccine in Africa is relatively recent and coverage is still incomplete, the GBD 2016 study showed that rotavirus vaccine coverage was negatively correlated with all-cause diarrhea. However, the fraction of diarrhea cases attributed to rotavirus varies substantially across Africa (6.5 to 64.2% in 2016). As the vaccine becomes more established, this situation will warrant further investigation.

Local estimates of diarrheal burden can be used to prioritize improved access to safe water and sanitation, which varies greatly between dense and sparse populations32,33; childhood-growth monitoring, which has improved in most regions of Africa but not universally34,35; delivery and uptake of vaccines, including the rotavirus vaccine36; and access to diarrheal care and prevention interventions for marginalized populations that live in remote regions or in areas of conflict.37,38 Nepal, for example, outpaced its neighboring countries in reducing diarrhea-related case fatality rates in part by implementing a district-level community intervention program.39 In addition, Brazil successfully used targeted interventions in the 1980s, when it drastically reduced infant mortality due to diarrheal diseases through the use of policy efforts aimed at the northeast of the country, a poorer region that had the highest burden in the country.40

As with any work of this scope, our results are subject to several limitations. First, to produce continent-wide estimates, we combined data from a broad range of sources, which required us to make assumptions about their usefulness and consistency. For example, whereas the prevalence of diarrhea was assessed with the use of the same, standard question across health surveys, such surveys rely on respondent-reported stooling patterns and, as such, are subject to recall and reporting bias. Second, there is also evidence of significant differences in risk within the group of children younger than 5 years of age.41 Owing to the nature of the data and methods we used, we are currently unable to parse mortality and morbidity estimates into finer age groups.13,42 Third, without an assessment of the interventions used across the continent over time, we are limited in the inferences we can make in this article.

Fourth, conversions from prevalence to incidence leveraged the GBD-modeled estimates and distribution of diarrhea severity. Incorporating cause-specific estimates of the incidence and severity of diarrhea would probably enhance the accuracy of the conversion and would serve as a valuable tool in the design of appropriate and effective interventions. Similar to the GBD 2016 study, which parsed all-cause diarrhea into percent attributable fractions for multiple causes,1,27 we are working toward cause-specific maps of mortality and morbidity for Africa. Currently, neither approach uses information about bloody stools to ascertain the severity or cause of the diarrheal episode because that information was not included in all the surveys. Although the conversion from incidence to mortality leverages various data sources1,13,27 and allows for variation in the case fatality rates according to country, year, sex, and age, it does not currently allow for variation in case fatality rates according to cause of diarrhea and does not incorporate the effects of coexisting conditions.

The data used in our analyses overlapped with but were not identical to the findings of the GBD 2016 study, and although our model had reasonable agreement at the country level with the data we used (Fig. S9 in the Supplementary Appendix), our estimates frequently differed from those of the GBD 2016 study (Fig. S12 in the Supplementary Appendix). We adjusted our estimates to align with those of the GBD 2016 study to maintain consistency with its results and for the purposes of using GBD-level analyses (e.g., case fatality rates) (Section 4.3 in the Supplementary Appendix). Our geospatial approach naturally borrows strength from neighboring areas and, as such, may smooth over extremely focal epidemics, such as those that have frequently been associated with cholera.

This work provides a foundation for several important directions for future research. First, combining these results with hospital-level, clinic-level, and causal agent–specific data may provide increased capacity to create targeted intervention strategies (e.g., coverage needs for the rotavirus vaccine). In the absence of data regarding causal factors, it is difficult to target interventions precisely because some interventions are cause-specific. Second, the exact spatial and temporal information about the implementation of past intervention programs ought to be matched to the corresponding trends in risk in order to look for the signatures of effectiveness. Finally, the approaches outlined in this study are directly applicable to other continents for which similar data sources are available. Expanding the estimates to all low- and middle-income countries will be the next step toward the goal of globally mapping diarrheal morbidity and mortality.

In conclusion, this study showed the marked local variation in childhood morbidity and mortality due to diarrhea across Africa. For every country in Africa, these estimates can be used to identify the regions to target interventions more precisely. Given that the vast majority of diarrheal diseases are attributable to preventable causes of diarrhea,1 many of these estimated deaths are likely to be preventable at the population and clinical levels.