Neonatal fecal abundance of Bifidobacterium longum subspecies infantis is not associated with anthropometric outcomes up to 6 months of age in Bangladeshi infants

B. infantis abundance in the infant gut may be associated with growth and health outcomes. However, these relationships have not been widely studied in settings where B. infantis is a dominant early-life commensal and growth faltering is prevalent. Here, we estimated associations between neonatal B. infantis abundance and anthropometric outcomes up to 6 months of age in generally healthy infants in Dhaka, Bangladesh; diarrhea and hospitalizations (at 1-2 and 6 months) were secondary morbidity outcomes. B. infantis stool absolute abundance was quantified by qPCR; for each infant, the primary exposure was mean abundance (0-28 days). Length-for-age, weight-for-age, and weight-for-length z-scores were derived at birth, 2, 3, and 6 months. Neonatal B. infantis abundance had a bimodal distribution, with 63% of infants having detectable B. infantis by 28 days of age. Anthropometric z-score distributions were shifted down, with means below zero at all ages. Neonatal B. infantis abundance was not associated with any anthropometric outcome at 2, 3, or 6 months of age (n=830), or with the risks of diarrhea or hospitalizations. The lack of association of neonatal B. infantis abundance with growth outcomes suggests that promoting early B. infantis colonization is unlikely to improve growth in populations with postnatal faltering.