This representative study of Nigerian children U5 years old shows a high prevalence of malaria in this vulnerable group. Our result shows 27% prevalence of U5 malaria diagnosed by microscopy was found in Nigeria. This reveals a fraction of the huge national burden of malaria in Nigeria. Over 93% of malaria cases and related deaths were recorded in Africa, with Nigeria ranking up there as the most endemic country with 25% and 24% of global malaria cases and deaths, respectively (7).
While no association was recorded for age and sex, we found that the highest prevalence of malaria among U5 children in our sample population was recorded in children aged 4-5 years [48-59 months] (33.4%). The absence of definite stratification within this age group suggests that all children under 5 years of age are at high risk. In fact, a seasonal malaria chemoprevention program has been piloted, and shown to significantly reduce malaria in under 5 children participating in the mass drug administration program in different areas of diverse malaria transmission intensity (14-17). Some economic benefit has further been attributed to seasonal malaria chemoprevention of all under 5 children (16, 18), with recommendation for this approach to be integrated into the health system in endemic areas.
The study did not observe any sex difference in U5 malaria prevalence in Nigeria. Our finding is in agreement with other studies in U5 children in Ethiopia (19) and Burkina Faso (20). In addition to demographics, another individual level factor assessed was the availability and use of ITNs by U5 children, the night before the survey. Although the prevalence of malaria infection decreased when at least some children slept under the ITNs, there was no definite association between use of ITNs the night before and U5 malaria in the study population. While other studies had reported up to 10-fold decrease in under 5 malaria due to use of ITNs (19), our data suggest that the use of ITNs alone may not be sufficient for effective malaria control and elimination as opined by others (21).
At the household level, we found strong association between several assessed demographic and socioeconomic determinants. High number of household members but not the number of U5 children significantly increased malaria risk, especially when this number exceeds seven members. As previous studies have found that Anopheles mosquitoes are attracted to higher concentration of carbon dioxide as well as human odour (22), it is therefore plausible that larger households in our data are more likely to have an increased risk of mosquito bites.
Furthermore, our data suggest that children with educated mothers had less odds of malaria. As mother’s education is often used as a proxy for household wealth (23), previous studies have found a reduced risk of malaria in wealthier households (24). There is the consistent trend in association between the household wealth index, an indicator related to other household determinants that impact on malaria incidence, with the poor suffering the brunt of malaria cases and perhaps mortality. Maternal education profoundly affects the household perception of malaria preventive measures, including acceptability and practice of malaria control interventions (25). Putative causal relationship has been reported for the impact of mother’s level of education to U5 malaria (26). Wealth index is closely related to educational level and has been shown in this study to reduce malaria risks, consistently showing a negative association between household wealth and risk of under 5 malaria. Because wealth impacts other indices like education, housing, household nutrition, area of residence and health seeking behaviour, it is arguably a major determinant of U5 malaria (25, 27). Although malaria can be rightly described as a disease of poverty (28), no association was found in some studies between chronic malnutrition and U5 malaria (29), suggesting a more complex relationship.
Also, household domestic water sources that promote availability of stagnant water will directly impact the breeding capacity of malaria vectors, indirectly worsening malaria transmission among U5 children. Potable water resources and indoor residual spraying are key malaria intervention efforts targeted at the disease vectors that has recorded significant success in malaria transmission in several diverse settings (25, 30, 31). Indeed, termination of indoor residual spraying intervention was reported in a study to result in rebound of prevalence to epidemic proportion (32).
At the community level, residence in urban or rural areas can impact malaria infection in U5 children mainly related to associated factors like population density, proximity to favourable vector breeding sites, agricultural projects, and closeness to health facilities. Like other studies, we also found that residence in rural areas and suburbs can worsen malaria transmission among U5 children (33, 34). The low prevalence in urban areas may be related to population density and its impact on the efficacy of malaria control interventions. Stebbins et al (35) reported variation in the efficacy of ITNs in urban and rural areas, concluding that ITNs use in urban areas offer benefits beyond individual protection. This further implicates population density factors, which were not observed in rural settings with more sparse population. Children U5 in the Northwest region had the highest odds of U5 malaria. They account for the highest proportion of reliance on open well and spring water for their source of drinking water. Such water bodies are known for providing suitable breeding sites for the malaria vector.
However, urban and rural areas in SSA have starkly varying types of housing. Tusting et al implemented a geospatial model to estimate the prevalence of improved housing in Africa (36). Their study defined ‘improved housing’ as houses built with finished materials such as brick and cement, whereas ‘unimproved houses’ were houses built with natural materials such as mud, thatch and less likely to have door and window screens as well as suitable furniture for mounting ITNs. Although there has been significant improvement in housing type in the past decade, there remains vast areas with unimproved housing, mostly in rural settlements. Previous studies have also found that malaria risk is higher in rural areas (37).
The multilevel results show significant variation in the risk of U5 malaria across sampled clusters and to some lesser extent across households. About 54.8% of the contextual cluster level variance for malaria parasitaemia can be explained by individual, household and community level fixed effect predictors. Averaging of the cluster-level variations by State shows that the contextual variations in U5 malaria risk are lower in most States in the southern region and higher in States in the Northern region. The sharp decrease in the cluster level median odds ratio after controlling for individual, household and community-level factors, again signify the important role these factors play in malaria transmission/intervention. While a spatially explicit analysis was not performed in this work, there is likely a spatial pattern in our prevalence estimates, given that Nigeria has distinct climate, socio-economic and environmental characteristics between its region. We therefore believe that these are significant contributing factors to regional variations in U5 malaria transmission. It will be interesting to thoroughly investigate these regional variations in U5 malaria transmission within a spatial framework.