A subnational profiling analysis reveals regional differences as the main predictor of ITN ownership and use in Nigeria

Malaria is a major public health issue in Nigeria, with 100% of the population at risk [1]. The country has the highest proportion of malaria cases (27%) and estimated malaria deaths (30%) globally; nationally, the malaria burden accounts for 60% of outpatient visits to health facilities and 30% of child mortality [2]. The geographic spread of the malaria burden is heterogeneous in the country, with the highest prevalence among children ages 6 to 59 months in the North Central, North East and North West regions, and the lowest prevalence in the South East region [3].

To reduce the malaria burden, the Government of Nigeria, through the National Malaria Elimination Programme (NMEP) and in collaboration with partners, is scaling up malaria prevention and treatment interventions in line with the goals of the National Malaria Strategic Plan (NMSP) 2014–2020. Under this strategic plan, the NMEP is striving to increase insecticide-treated net (ITN) ownership coverage and raise awareness to increase ITN use [4]. The NMEP employs a mixed-model approach for ITN distribution that includes free mass distribution campaigns and continuous distribution of ITNs to supplement the mass campaigns. Continuous distribution relies on several routine health service delivery channels: immunization campaigns; antenatal care (ANC); the integrated maternal, newborn, and child health week; school-based distribution; community-based distribution; and, distribution through the commercial sector [3]. Between 2014 and 2016, more than 60 million ITNs were distributed, which helped increase household ownership of at least one ITN from 8% in 2008 to 69% in 2015 [2, 3, 5]. The majority of households (77%) received their ITNs through free mass distribution campaigns [3]. Following the recommendation by the WHO, the ITNs distributed by the NMEP have been long-lasting, insecticide-treated nets (LLINs) [6]. LLIN brands distributed in these mass campaigns include Duranet, Iconlife, Interceptor, Netprotect, Olyset and Permanet [3]. Household ownership of at least one LLIN also reached 69% in 2015 [3]. In Nigeria, most ITNs owned by households are LLINs, this is reflected in the matching proportions of households owning an ITN (68.8%) and households owning an LLIN (68.7%) in 2015 [3]. This indicates that the ITNs households own are LLINs. Therefore, in this study, both LLINs and nets that have been soaked with insecticides in the past 12 months will be referred to as ITNs.

To complement the ITN distribution efforts, the NMEP has also implemented advocacy, communication and social mobilization (ACSM) campaigns to improve knowledge of malaria prevention and control practices, create demand and increase the use of ITNs. Through these efforts, ITN use among the general population, children under 5, and pregnant women has increased significantly since 2008 [3, 7].

Despite the improvements observed in ITN ownership and use at the national level, large gaps remain to reach the goals of the NMSP 2014–2020 of universal access to ITNs and 80% ITN use among targeted populations by 2020 [8]. The increase in ITN ownership and use has also been uneven, with differences seen in household ITN ownership and use by place of residence, region of the country and household wealth quintile [3]. This study was conducted to guide future ITN strategies and investments to maximize impact, increase proportionate coverage and enhance progress toward the universal access target of all populations at risk of malaria. It examined sub-national profiles of household ownership of ITNs and ITN use in the general population to identify the best predictors of ITN ownership, use and which specific sub-groups to target.

This study examined sub-national profiles of household ownership of at least one ITN and ITN use in the general population. The CHAID analysis indicates that region of the country is the best predictor of both household ITN ownership and ITN use. Other significant predictors of both outcomes are household size, head of household education level, household wealth quintile, and place of residence.

The heterogenous transmission of malaria across Nigeria may best explain why region of the country is the most significant predictor. The NMEP focuses its ITN distribution efforts in areas with a high malaria burden. Across the three northern regions, the prevalence of malaria in children under five ranges from 26 to 37% compared with 14 to 19% in the three southern regions [3, 10, 11]. The NMEP uses free mass distribution of ITNs in these areas, a strategy that has been proven to dramatically increase household ITN ownership [12‐14]. Possession of ITNs through these means has been shown to increase ITN use [15]. The NMEP’s ITN distribution strategy is coupled with ACSM activities, which previous studies found to significantly generate demand for and increase the use of ITNs [16‐18]. As to the regional differences in household ITN ownership, the concentration of ACSM activities may contribute to the disproportionate use of ITNs. Household ITN ownership and use were observed to be the highest in the northern regions compared with the southern regions, with differences across regions. The regional differences are also supported by the multiple logistic regression findings, with the odds of a household owning an ITN being five times greater in the North West region compared with the North Central region.

The ITN distribution strategy may also account for the disproportionate ITN ownership across household sizes. Medium to large-size households were found to have higher ownership in the North East, North Central, South South, and South West regions compared with small-size households. de Beyl et al. noted a similar result, which found that larger size households were more likely to register and receive ITNs [19]. In addition to mass distribution campaigns, the NMEP uses other distribution channels, such as schools, ANC and immunization clinics. Employing these channels has been shown to help maintain ITN coverage and reduce inequities among vulnerable populations [20, 21]. However, use of these channels leaves a gap in coverage for households without young children or a woman who has attended ANC in the past 2 years to obtain an ITN [22].

Despite higher ITN ownership among medium to large-size households, ITN use was greater in small-size households compared with large-size households. These results were comparable with recent studies, which found very low intra-household saturation with ITNs among large households following mass distribution campaigns [13, 23‐26]. Higher use among smaller households may be indicative of larger households not having enough ITNs to cover everyone in the household. Several studies have discovered that improving household access and having sufficient ITNs were significant predictors of ITN use [14, 24‐28]. Households with higher levels of education generally had higher ITN ownership, although this was a significant predictor in the North Central, South South and North West regions only; comparable gaps were found in other studies examining equity in coverage [29, 30].

The NMEP has increased its focus on equity among households in the lowest wealth quintiles and in rural areas. Children in the lowest wealth quintiles had a disproportionately greater burden of malaria (64%) compared with children in the highest wealth quintiles (13%) [3]. For children in rural areas, the prevalence of malaria was significantly higher (56%) compared with children in urban areas (24%) [3]. There is an overlap between these populations, and among those living in rural settings, more than 60% are in the lowest two wealth quintiles. Among those living in urban settings, more than 75% are in the top two wealth quintiles [4]. Analogous to other countries with a high malaria burden, to help increase ITN ownership across these households, the NMEP employed free ITN distribution [12, 15, 31‐33]. This has led to households in both the lowest wealth quintiles and in rural areas having higher ITN ownership [3]. Most households in rural areas were more likely to own an ITN, except for those in the South East region, where households in urban areas had higher ITN ownership. There was variability in ITN use across urban and rural settings. In the South West and South East regions, ITN use was higher in urban areas, and the opposite was observed in the North Central and South South regions. This variance may be linked to the higher ITN ownership found in the urban areas of the South East region and in the rural areas of the North Central and South South regions. Higher ITN use among those in the lowest wealth quintiles and in rural areas reflects the NMEP’s achievements in reducing inequity, because other research has found these populations to have the lowest ITN ownership and use [12, 34].

The CHAID analysis aids in the understanding of variables that affect household ITN ownership and ITN use in the general population. Attention to the sub-groups identified in this research study may help Nigeria progress toward achieving the goal of universal ITN coverage and increase the overall use of ITNs in the general population. The gain index table provides specific information on the sub-groups to better inform intervention strategies. Efforts focused on increasing net ownership in small-size households in the South West (Node 21), North Central (Node 12), and South Central (Node 22) regions should be considered, as these areas include 43% of households not owning an ITN, though accounting for 29% of the population. To increase ITN use in the general population, increased focus needs to be placed on sub-groups containing households in the lowest and fourth wealth quintiles in the urban areas of the South South region (Node 45), the top two wealth quintiles in the South East region (Node 50), and the second and middle wealth quintiles in rural areas of the North Central region (Node 43), which account for 31% of the population that do not use ITNs.

Nigeria has made significant progress in expanding ITN coverage and generating demand for and use of ITNs over the past decade. Despite these efforts, large gaps remain to achieve universal ITN access and 80% ITN use. This study reveals the regional differences in ITN ownership and use throughout Nigeria and identifies specific subgroups among small-size households in the South West, North Central and South Central regions. It also identified specific sub-groups among households in the lowest and wealthiest quintiles in the southern regions that could be targeted and fill the coverage and use gaps.