Geographical and temporal variation in reduction of malaria infection among children under 5 years of age throughout Nigeria

Abstract

Introduction: Global progress in reducing malaria has stalled since 2015. Analysis of the situation is particularly needed in Nigeria, the country with by far the largest share of the burden, where approximately a quarter of all cases in the world are estimated to occur.

Methods: We analysed data from three nationwide surveys (Malaria Indicator Surveys in 2010 and 2015 and a National Demographic and Health Survey in 2018), with malaria parasite prevalence in children under 5 years of age determined by sampling from all 36 states of Nigeria, and blood slide microscopy performed in the same accredited laboratory for all samples. Changes over time were evaluated by calculating prevalence ratio (PR) values with 95% CIs for each state, together with Mantel-Haenszel-adjusted PRs (PR_adj) for each of the six major geopolitical zones of the country.

Results: Between 2010 and 2018, there were significant reductions in parasite prevalence in 25 states, but not in the remaining 11 states. Prevalence decreased most in southern zones of the country (South West PR_adj=0.53; South East PR_adj=0.59; South South PR_adj=0.51) and the North Central zone (PR_adj=0.36). Changes in the north were less marked, but were significant and indicated overall reductions by more than 20% (North-West PR_adj=0.74; North East PR_adj=0.70). Changes in the south occurred mostly between 2010 and 2015, whereas those in the north were more gradual and most continued after 2015. Recent changes were not correlated with survey-reported variation in use of preventive measures.

Conclusion: Reductions in malaria infection in children under 5 have occurred in most individual states in Nigeria since 2010, but substantial geographical variation in the timing and extent indicate challenges to be overcome to enable global malaria reduction.

Keywords: diagnostics and tools; epidemiology; malaria; prevention strategies.

Figure 1

Geographical and temporal heterogeneity of malaria parasite prevalence in children under 5 years old in Nigeria. Data are analysed for all 36 states (excluding Borno state in 2015); the central Federal Capital Territory incorporating Abuja is not analysed as it could not be representatively sampled. The names of individual states are shown in the top map, and the grouping into six geopolitical zones is given in table 1. Data are derived from three previous surveys, made available for analysis from http://mics.unicef.org/surveys with permission by the UNICEF Multiple Indicator Cluster Surveys (MICS) team. All numbers are given in table 1, online supplemental table 1. MIS, Malaria Indicator Survey; NDHS, National Demographic and Health Survey.

Figure 2

Prevalence ratios (with 95% CIs) comparing malaria parasite infection in under 5-year old children in 2018 with 2010 in each state and geographical zone in Nigeria. Although there was marked variation, significant declines in prevalence were seen in many states, indicated by ratios with 95% CIs to the left of the line. For each of the six major geographical zones of the country, the overall Mantel-Haenszel-adjusted prevalence ratio (PR_adj) is plotted with a purple diamond symbol (with 95% CIs), showing significant overall declines: North-West PR_adj=0.74 (0.68–0.81); North East PR_adj=0.70 (0.61–0.81); North central PR_adj=0.36 (0.32–0.42); South West PR_adj=0.53 (0.46–0.61); South East PR_adj=0.59 (0.49–0.72); South South PR_adj=0.51 (0.43–0.61). All numbers and P values are given in table 1, and in online supplemental table 1.

Figure 3

Decrease in malaria prevalence in under 5-year old children shows significant heterogeneity over time and geographical area. Prevalence ratios (with 95% CIs) compare the malaria parasite infection in under 5-year old children in individual states and geographical zones of Nigeria in the intervals between 2010 and 2015 (left hand panel), and between 2015 and 2018 (right hand panel). For each of the six major geographical zones of the country, the overall Mantel-Haenszel-adjusted prevalence ratio (PR_adj) is plotted with a purple diamond symbol with 95% CIs. Between 2010 and 2015, significant declines are seen in all zones, except the North East where the decline is borderline significant, and the declines are more marked in the South of the country. Between 2015 and 2018, significant declines were seen overall in North central zone and North-West zone, borderline significant in North East. (Data for Lagos state are not plotted as there was an indefinite PR due to zero positive slides in 2015, and Borno state is not included due to lack of data for 2015). All numbers and P values are given in online supplemental table 1.