Statistical Analysis
deaths
REGRESSION, SECONDARY
This secondary analysis was conducted in 2023. The sample size for this analysis was fixed by enrollment in the MORDOR Niger trial, which was powered to detect a community-level effect of azithromycin MDA on mortality among children aged 1 to 59 months over 2 years. Details of sample size calculations have been reported previously.Descriptive summaries included community-level baseline characteristics by arm using numbers (percentages) for categorical variables and means (SDs) or medians (IQRs) for continuous variables. Crude mortality rates were calculated as the count of deaths per community divided by the community-level person-time at risk, and 95% CIs were computed assuming a Poisson process. Crude mortality rates were examined by distance to a primary health center, which was categorized in 1-km increments up to 10 km.Negative binomial regression was used to examine the association of azithromycin MDA with mortality by distance to a primary health center at the community level. Models included the number of deaths per community as the outcome, covariates for treatment arm, mean child age per community at baseline, distance to a primary health center, and the interaction between treatment arm and distance to examine multiplicative effect modification. Community-level person-time at risk was included as an offset. Mean community age was included as a covariate because age is a known risk factor for mortality, with younger ages experiencing higher mortality. Community-level clustering was taken into account by the dispersion parameter in the model. To aid interpretation of the interaction, the association of azithromycin MDA with mortality was estimated at specific distances from health centers (1 km, 5 km, and 10 km). The 5-km increments were chosen because they align with thresholds at which the Niger health system distributes different community services. A sensitivity analysis was conducted using Poisson regression models in a similar format with robust SEs to account for clustering. The Johnson-Neyman procedure was used to determine regions of significance assuming an α of .05.