Multidisciplinary Delphi consensus statement on minimal standards for clinical metadata and end points in microbiome studies.

The lack of harmonization for microbiome-based clinical studies represents a critical issue for microbiome researchers and stakeholders, although microbiome research and clinical studies on the gut microbiome have been intensively conducted for more than a decade. The selection of a minimum metadata set to be analysed and reported during clinical studies with microbiome outcomes, the identification of reference materials, the definition of standardized sampling procedures and data analysis protocols, and the choice of unified clinical end points are still lacking. The two-round Delphi survey, conducted within the framework of the Horizon Europe Human Microbiome Action (HMA) consortium, aimed to standardize metadata collection, sampling procedures, data generation and sharing, and standard operating procedures for aspects of gut microbiome-based clinical studies beyond outcomes. The process involved 72 scientists and experts worldwide in the first round and 61 experts in the second round, with an 85% participation rate from the first to the second round. On the basis of the outcome of the Delphi survey, the HMA consortium provided 15 recommendations that might be taken up by the community at large to promote coherence and harmonization in the way microbiome clinical research is and will be performed. The recommendations mainly focus on the gut microbiome and diseases associated with the gastrointestinal tract and gut-organ axes.