This cluster-randomized controlled trial is designed to address linear growth faltering in 6-12-mo-old Bangladesh infants through a proof-of-concept package of interventions to a) increase intake of high quality protein and b) control enteric pathogens.

Stunting a major public health problem in Bangladesh, where 36% of children under the age of five are too short for their age. While dietary data indicate that protein intakes of infants and young children are largely in line with requirements, the extent to which requirements derived for healthy infants and young children are relevant in the context of frequent infections remains an important research question.

Recent investigations indicate widespread pathogen carriage among Bangladeshi infants, with virtually all having at least one detectable pathogen in nondiarrheal stools by six months of age. Campylobacter and pathogenic E. Coli predominate in this setting. Enteric pathogens can compete with the host for available nutrients or alter nutrient metabolism. Acting via environmental enteric dysfunction, they can alter both digestion-through loss of digestive enzymes-and absorption of nutrients. Microbial translocation may further alter specific amino acid requirements.

Even in the absence of acute diarrheal disease, enteric pathogen carriage is strongly associated with linear growth faltering. Combining the effects of high pathogen burden and poor diet, as indicated by low energy and protein from complementary foods, observational evidence suggests that the potentially preventable length-for-age Z-score deficit may be as high as 0.98.

The present trial will test the combination of a) protein supplementation in the form of a protein-rich blended food or an egg, both fed daily to infants 6-12 months of age, and b) azithromycin treatment for enteric pathogens. The primary outcome will be change in length-for-age Z-score from the 6 to 12 months. Biochemical, microbiological and clinical intermediates will be measured to inform our secondary aims.

Inclusion Criteria:

• Born to women enrolled in ongoing community trial (NCT02909179) over a one-year period

Exclusion Criteria:

• Born to women not registered as part of the ongoing community trial (NCT02909179)

Participants, care providers, investigators and outcomes assessors will be blinded to the azithromycin or placebo interventions. Neither participants nor outcomes assessors will be masked to the nutrition interventions. Investigators will be masked to the nutrition interventions.