Amino acid-based formula (AAF) feeding is a notable risk factor closely associated with the development of Clostridioides difficile-associated disease (CDAD) in infants and toddlers under two years, associated with reduced Bifidobacteria levels and increased susceptibility to C. difficile infection.
Key Findings
Results
Amino acid-based formula (AAF) feeding was identified as a significant risk factor for CDAD in infants and toddlers under two years of age.
The study investigated 27 CDAD cases in infants and toddlers under two years of age.
AAF feeding was described as 'a notable risk factor closely associated with the development of CDAD in infants.'
Infants and toddlers were previously considered to be exempt from Clostridioides difficile-associated disease, making this finding notable.
The study design allowed comparison between AAF-fed and normal formula (NF)-fed infants.
Results
Infants fed with AAF exhibited reduced levels of Bifidobacteria in their fecal microbiomes compared to normal formula-fed infants.
Bifidobacteria have been previously reported to compete with C. difficile.
The reduction in Bifidobacteria was observed through fecal microbiome analysis of AAF-fed infants.
The reduction in Bifidobacteria represents a plausible mechanistic link between AAF feeding and increased CDAD susceptibility.
This microbiome alteration was considered a key biological finding connecting diet and infection risk.
Results
Mice transplanted with feces from AAF-fed infant donors were more susceptible to CDAD than mice receiving feces from normal formula-fed donors.
A fecal microbiota transplantation mouse model was used to establish causality between AAF-associated microbiome changes and CDAD susceptibility.
The mouse experiment compared recipients of feces from AAF-fed infant donors versus normal formula (NF)-fed donors.
Increased susceptibility to CDAD in the AAF fecal transplant group supports a microbiome-mediated mechanism.
This in vivo experiment provided experimental evidence beyond the clinical observational findings.
Background
C. difficile infection can cause severe gastrointestinal symptoms in infants and toddlers under two years, a population previously considered exempt from CDAD.
Recent studies had begun to report C. difficile infection causing severe gastrointestinal symptoms in this age group prior to this study.
The study identified 27 CDAD cases in infants and toddlers under two years.
Risk factors related to CDAD in infants had previously been unknown.
The authors note that 'infants and toddlers were previously considered to be exempt from Clostridioides difficile-associated disease.'
What This Means
This research suggests that a specialized type of infant formula called amino acid-based formula (AAF), which is often used for babies with severe food allergies or digestive problems, may significantly increase the risk of a serious gut infection caused by a bacterium called Clostridioides difficile (C. difficile). The researchers studied 27 infants and toddlers under two years old who developed C. difficile-associated disease and found that AAF feeding was strongly linked to getting this infection. Babies fed AAF had lower levels of beneficial Bifidobacteria in their gut — bacteria known to naturally compete with and suppress C. difficile — which may explain why they were more vulnerable to infection.
To confirm that the gut bacteria changes caused by AAF were responsible for the increased risk, the researchers transplanted fecal samples from AAF-fed babies into mice. Those mice became more susceptible to C. difficile infection compared to mice that received fecal samples from babies fed standard formula. This experimental step strengthened the evidence that AAF feeding alters the gut microbiome in a way that removes a natural protective barrier against C. difficile.
This research matters because young infants have historically been thought to be protected from serious C. difficile disease, and the risk factors in this age group were poorly understood. These findings suggest that the type of formula an infant receives could meaningfully affect their vulnerability to this infection, and that maintaining healthy levels of Bifidobacteria may be an important factor in protection. This could have implications for how clinicians monitor and care for infants who require AAF feeding.
Wang L, Luo J, Geng J, Zheng X, Xu Y, Qiu C, et al.. (2026). Amino acid-based formula feeding is associated with increased risk of Clostridioides difficile-associated disease in children younger than two years.. Gut microbes. https://doi.org/10.1080/19490976.2026.2719259