Effect of biannual azithromycin distribution on antibody responses to malaria, bacterial, and protozoan pathogens among children: A cluster-randomized, placebo-controlled trial in Niger

Abstract

Background: The Macrolides Oraux pour Reéduire les Deécès avec un Oeil sur la Résistance (MORDOR) trial in Niger, Malawi, and Tanzania found that biannual mass distribution of azithromycin to children younger than 5 years led to a 13.5% reduction in all-cause mortality. Additional endpoints in the trial have attempted to elucidate the mechanisms for mortality reduction. In this pre-specified secondary analysis, we assessed the effect of azithromycin compared with placebo on IgG-based measures of infectious disease exposure with a multiplex bead assay that included antigens to malaria parasites (Plasmodium falciparum, P. vivax, P. malariae, P. ovale), bacterial pathogens (Campylobacter spp., enterotoxigenic Escherichia coli, Vibrio cholerae, Salmonella enterica, Streptococcus pyogenes) and protozoans (Cryptosporidium parvum, Giardia duodenales). Methods and Findings: Thirty communities in rural Niger were randomized 1:1 to biannual distributions of azithromycin or placebo among children ages 1-59 months. The analysis included 5,642 blood specimens collected from 3,814 children ages 1-59 months, measured at 6, 12, 24, and 36 months of follow-up in a repeated cross-sectional design. Campylobacter spp. seroprevalence averaged over all study visits was lower in azithromycin communities compared to placebo (91% vs 94%, difference = -3%, 95% CI: -5%, -1%; P=0.03), which corresponded to a 29% lower seroconversion rate (1.30 versus 1.84 seroconversions per year, hazard ratio = 0.71, 95% CI: 0.56, 0.89; P=0.004). Antibody-based measures of infection with P. falciparum and group A streptococcus were consistently lower in azithromycin communities, but were not statistically different from placebo, and there were no other differences across pathogens. Strengths of the study included masking of participants, investigators, and analysts, high treatment coverage, large sample size, and objective outcomes. Principal limitations included the timing of blood collection with respect to treatment (approximately 6 months later, which could have missed transient effects in the weeks immediately following treatment), and the durability of IgG response following clearance of infection. Both limitations would lead the trial to under-estimate effects on antibody-based measures of infection. Conclusions: The reduction in Campylobacter spp. despite these limitations suggests an effect on carriage, findings which align with an independent metagenomic analysis of rectal swabs collected in the same villages and with previously reported reductions in dysentery-associated mortality. Given significant sequelae of Campylobacter infection among preschool aged children, our results support at least one possible mechanism through which biannual mass distribution of azithromycin likely reduced mortality in this study population.