Integrated housing quality and insecticide-treated net use: propensity score methods for childhood anemia prevention in The Gambia

BACKGROUND: Childhood anemia remains a critical public health challenge in sub-Saharan Africa, with malaria being a major contributing factor to its burden. Although insecticide-treated nets (ITNs) and improved housing are established malaria prevention strategies, their combined associations with childhood anemia are poorly understood. We examined the independent and joint associations of housing quality and ITN use with childhood anemia in The Gambia, using propensity score-weighted methods. METHODS: We analyzed data from 4155 children aged 6-59 months in the Gambia Demographic and Health Survey 2019/20. Housing quality was defined as having improved floor, wall, and roof materials in the household. ITN use was defined as sleeping under an ITN the night before the survey. We estimated propensity scores for each exposure and used inverse probability of treatment weighting (IPTW) to fit marginal structural models. Interaction was assessed on both multiplicative and additive scales using the relative excess risk due to interaction (RERI) with bootstrap confidence intervals. Stratified analyses examined effect modification by urbanicity and malaria transmission intensity. RESULTS: The weighted prevalence of anemia was 46.5%. Good housing quality (OR: 0.75; 95% CI 0.65-0.86) and ITN use (OR: 0.79; 95% CI 0.70-0.89) were independently associated with reduced anemia. A significant positive RERI of 0.45 (95% CI 0.11-0.67) indicated sub-additive interaction, the combined protective effect was less than the sum of individual effects. Protective associations were concentrated in urban areas (Housing OR: 0.77; ITN OR: 0.67) and low-transmission regions (Housing OR: 0.70; ITN OR: 0.70), with no significant effects in rural or high-transmission settings. E-values of 2.00 and 1.85 suggested moderate robustness to unmeasured confounding. CONCLUSIONS: Housing quality and ITN use independently reduce childhood anemia but partially substitute for each other rather than acting synergistically. The concentration of effects in urban and low-transmission areas suggests that in high-transmission settings, additional interventions beyond housing improvements and ITN use may be required. These findings have implications for integrated malaria control and anemia prevention strategies in The Gambia and other similar endemic settings.