Socio-demographic and economic inequity in the use of insecticide-treated bed nets during pregnancy: a survey-based case study of four sub-Saharan African countries with a high burden of malaria

Malaria is a mosquito transmitted disease caused by one of five plasmodium species. It is a major cause of mortality and morbidity in tropical and subtropical regions of the world, where it is endemic to 90 countries, placing216 million people at risk [1, 2]. According to the WHO world malaria report, in 2020, malaria was responsible for 241 million cases and 627,000 deaths [2]. The vast share of malaria cases and particularly deaths, occur in Africa (93% of worldwide deaths). Nigeria reports the largest share of cases globally (27%), followed by the Democratic Republic of the Congo (10%), Mozambique(5%), and Uganda (4%) [2].

Pregnant women are a special group at high risk of malaria infection, and severe complications, primarily due to impaired glucose metabolism and cell-mediated immunity (CMI). Prevalent complications include miscarriage, stillbirth, preterm birth, anemia, and intrauterine growth restriction [1]. A total of 25 million pregnancies are at risk of malaria related complications in sub-Saharan Africa each year [1, 3]. Determinants of severe disease include poor immune health, gravidity, trimester of pregnancy and presence of co-morbidities [3].

Two common malaria preventative measures for pregnant mothers are the use of intermittent preventative treatment using anti-malarial medications, and timely utilization of long-lasting, insecticide-treated nets (LLINs).Use of insecticidal bed nets such as LLIN is found to be an effective public health tool for control of malaria, especially among under-five children and pregnant women (especially in Africa) — the two most vulnerable groups [4]. A recent review by Cochrane [5], and multiple recent studies [6, 7] have clearly demonstrated a strong correlation between the use of ITNs and reduction in stillbirths, increase in birth weight, and a reduction in anemia and parasitemia levels among pregnant women. In addition to their use among pregnant women and children, ITNs generally reduce vector density [8].

Despite global investments in malaria eradication and mitigation efforts, including the dissemination of ITNs to vulnerable communities, the goal of widespread malaria control among pregnant women has yet to be realized in many African countries. Two explanations have been forwarded. The first is sub-optimal distribution of ITNs. Only an estimated 17% of ITNs have been distributed in sub-Saharan Africa, the region of the world that is most greatly affected [3]. This has been blamed by the WHO on supply chain and logistics shortcomings [4]. The second explanation, though not well understood, is related to the adoption and regular use of ITNs by pregnant women. Relationships with health workers, cost, distance to distribution points, knowledge of prenatal care and local environmental and sociocultural factors have been proposed to influence ITN use [1]. Other explanations such as discomfort with ITN use, and perceived low mosquito density have also been proposed by researchers [9].

Addressing these challenges requires an informed multidisciplinary approach that includes (1) the acceleration of programs that integrate malaria prevention with maternal and reproductive health, (2) increased provisioning of resources to the most needy groups, and (3) the development of innovative delivery approaches (4).

As part of routine antenatal care (ANC), ITNs are used to prevent malaria in pregnancy. This tool has been proven to be highly effective in all parts of the world as an effective method of reducing human–vector contact and thereby decreasing morbidity and mortality due to malaria. Despite the presence of such effective malaria preventive tool, the prevalence of malaria among pregnant women in sub-Saharan countries remains high, resulting in significant morbidity and mortality. This needs characterization of ITN utilization among pregnant women for targeted intervention. Thus, the current study was designed to analyze ITN utilization in African countries with the high burden of malaria such as Nigeria, Uganda, Democratic Republic of Congo (DRC), and Mozambique. In light of this ongoing problem, the specific purpose of this study was to investigate sub-national and sociodemographic disparities in ITN use among pregnant women by using data from the Demographic and Health Surveys of 2003, 2008, 2011, 2013, 2016 and 2018, and Multiple Indicator Cluster Surveys. The findings of this study are believed to support national and regional efforts to accomplish the Sustainable Development Goals (SDGs) in the respective countries, which includes goals of universal health coverage and ultimately reduced inequities.

The use of ITNs is one of the most effective and efficient strategies used to prevent malaria infection during pregnancy [25]. ITNs have also been shown to reduce malaria episodes among children underfive years of age by approximately 50%, and to reduce all-cause mortality by 17% globally [26]. This study examined economic, educational, urban/rural setting, and subnational geographic determinants of ITN usage among pregnant women in the high-malaria-burden countries of Nigeria, the DRC, Mozambique, and Uganda. The findings from our study show that being in the highest wealth quantile, attaining higher educational level and living in urban areas increased the likelihood of ITN usage.

Based on Difference as a measure of absolute health inequality, the economic status-based inequality assessment indicated that ITNis more utilized in economically better-off women in most DHS time points for Nigeria, DRC, Uganda and Mozambique. Similar findings were documented in Kenya and Tanzania [27, 28]. This shows disproportionate malaria risk meaning the risk of being bitten by a mosquito is way higher in the poor. Although, slight inequality was observed by complex measures (PAR, PAF) in all five surveys in Nigeria, in terms of PAR, ITNutilization in the advantaged survey populations across all countries is still higher than the national average. In case of PAF, the difference between advantaged groups in terms of ITNutilization is five times the national average in Nigeria in 2008 but became ten times in 2011. The same is true for DRC, where PAF measures increased from being thirty-five to forty-five times the national average in 2007 and 2017 respectively. This shows that there's a disproportionate risk of malaria among both the rich and poor. Inequalities like these should be taken into consideration while implementing interventions in view of risk based deployment of interventions like health education targeting low economic and education groups.

Our analysis has shown that ITN utilization was generally highest among the wealthiest quintiles, but usage increased across survey years for most economic groups. This finding corroborates studies from Kenya, Tanzania, and Uganda, which found that poverty was an impediment to the purchase of mosquito nets both untreated and treated [9, 27, 29]. The poorer economic strata were less likely to own an untreated net, acquire an ITN, or express a desire to pay for one. Charging for nets has been linked to high levels of adoption (up to 50%) among the lowest economic quintile, but this has only happened in regions where nets have been aggressively marketed [30]. Despite this finding, data analyzed in this study from Nigeria and Uganda indicated that economically disadvantaged pregnant women were more likely to utilize ITNs. ITN usage disproportionately benefit the poor since the wealthy are more likely to live in less malaria-prone areas,with less risks as a result of completed houses, covered eaves that minimize mosquito exposure, glass windows and/or screens. Poorer households are more likely to live in areas with inadequate drainage systems where mosquito breeding sites are abundant, and in close proximity to livestock, making household members more vulnerable to mosquito bites and raising the perceived need for ITN usage [31, 32]. In a recent study from Mozambique, families in the poorest wealth tertile (33.3%) had higher likelihoods of sleeping under an ITN (AOR 2.36; 95^th percentile CI: 1.16–4.81) compared to the wealthiest ones [33]. Because of their economic advantage, the wealthy may be more likely to investigate and employ malaria preventive measures such as indoor residual spraying (IRS) or the use of insect repellents [25, 32]. In contrast, these alternatives may be prohibitively costly for poorer pregnant women, resulting in a preference for a freely-provided ITN [33].

In all the years except for 2007, inequalities were observed across Nigeria, the DRC, Mozambique, and Uganda by educational attainment (± secondary education).. Recent studies from Kenya and Ethiopia lend credence to this finding, where the highest proportion of ITN users were women who were more highly educated. Enrollment in higher education or attaining secondary level of education was found to determine ITN usage by positively influencing care seeking behavior and use of ITN in pregnancy [34]. Some African studies have also shown a link between education and increased usage of ITNs and other vector control strategies [35, 36].

In contrast, a cross-sectional survey from Tanzania reported no link between education level and use of ITNs [37]. In Nigeria, a recent study found no significant relationship between degree of education (p = 0.269) and use of ITNs [38]. On the other hand, a study from Ethiopia found that increasing educational attainment was a statistically significant positive explanatory factor for the use of ITNs among pregnant women. Extrapolating these findings to Ethiopia's rural areas, where approximately 85% of the population has relatively lower educational attainment, ITN utilization is expected to be much lower in these sections of the nation [39]. This finding suggests that a greater degree of education may be necessary to influence malaria preventive and control intervention uptake [36, 40]. It is important to note that more qualitative research is needed regarding the reasons for ITN use. Without such data, it is difficult to determine if ITN usage is simply a by-product of supply chain logistics, i.e. where they are being sent, and proximity. It is equally difficult to disentangle the causes of ITN usage when factors that are associated with ITN usage are often interrelated where wealthy people probably have higher education levels and may be more likely to live in urban settings. urban–rural setting has been linked with ITN usage, as has educational attainment;, however, the actual causative agent, urban/rural setting, educational attainment, a combination of the two, or an unknown third component, is more difficult to assess.

In our analysis of survey data from the DRC, ITN usage was positively associated with educational attainment in all survey years except for 2007, when educational attainment was negatively correlated with ITN usage. In a study conducted in the DRC at approximately the same time (2007), it was found that women with a high school degree or higher were 1.3 times more likely to use ITNs (OR = 1.3; 95^th percentile CI: 1.085–1.611) compared to those with only a primary school education [41]. Increased education, particularly for young women, has been linked to a number of positive health outcomes, including lower newborn and maternal mortality, in this study as well as others from Sub-Saharan Africa [41].

Our results suggest that in Nigeria in the years 2003, 2008, 2016, and 2018, rural pregnant women were more likely than urban pregnant women to use ITNs.This supports previous findings that investigated variation in ITN utilization between rural and urban pregnant women in Nigeria. In that study, 86.1% of rural residents utilized ITNs, compared with 74.1% among urbanites [42]. Similarly, in Cameroon and Sierra Leone, it was discovered that, following a countrywide mass distribution of ITNs, rural residents were more likely to adopt regular ITN usage compared to urban dwellers [43]. Finally, in a study similar to ours, that extracted data from the Ghana 2014 DHS and the 2016 Malaria Indicator Survey, it was concluded that, in both survey years, increasing net usage was associated with living in rural settings [31]. The possible explanation for this might be, in most countries, the malaria burden is higher in rural areas compared to urban settings and therefore intervention coverage is higher in rural settings.

Conversely, many recent studies from Nigeria [44] and other sub-Saharan African countries, such as Ghana [45], Equatorial Guinea [46] and Senegal [26] have reported greater ITN usage in urban areas. A Malawian cross-sectional research of 528 respondents also indicated that after a social marketing campaign, households generally owned more ITNs, but in urban areas, the rate grew to 29%, compared to 6.4% in rural areas [47]. Women in rural areas were similarly less likely to use ITNs.This could be due to an imbalance in ITN outlets favoring urban areas, a lack of education in rural areas, difficulty in creating marketing campaigns in rural settings, or a lack of the economic resources to purchase ITNs in rural regions [40]. In areas where rural residents have possessed ITNs in Nigeria and Tanzania, studies in the past years have reported that actual utilization remains low [48, 49]. It is imperative that in addition to the collection of more robust qualitative data from survey participants, and more complex statistical models that tease out causality, that geographic mapping of distribution sites is incorporated, so that researchers can assess the influence of simple accessibility. Once there is a better understanding of causes of ITN usage, and differences between countries and environments, subnational tailoring of resource allocation can be much more effective.

The observed difference in ITN use across all dimensions of inequality in all the four countries was highly pronounced. ITN utilization was generally highest among the wealthiest quintiles. There was an association between ITN usage and increasing educational attainment. Similar finding was reported for subnational regions. There was an overall increasing trend of ITN use over the survey times in all the four countries. This calls for targeted intervention by stakeholders to improve ITN use among pregnant women. Tailored combination of cost-effective interventions could be considered to achieve synergy and maximize the gains.