Variation in urobiome composition over time in asymptomatic individuals with spinal cord injury and disease using intermittent catheterization

Urinary tract infection (UTI) remains the most common infectious complication among individuals with neurogenic lower urinary tract dysfunction (NLUTD) due to spinal cord injury or disease (SCI/D). Despite widespread reliance on microbiological and symptom-based criteria for UTI diagnosis, significant ambiguity persists-especially in distinguishing clinically meaningful change from normal variability in urinary analysis results. This uncertainty contributes to overdiagnosis, inappropriate antibiotic use, and antimicrobial resistance. The present study sought to operationalize "normal variability" of the urinary microbiome (urobiome) among adults with NLUTD due to SCI/D. Using repeated samples collected from asymptomatic individuals over time, we analyzed inter- and intra-individual microbial composition to determine stability and fluctuation under baseline conditions. We observed wide intra- and inter-individual variability, substantial overlap between asymptomatic and pre-symptomatic states, and a consistent predominance of genera conventionally labeled as "uropathogens" including Escherichia/Shigella, Klebsiella, Enterococcus, Staphylococcus, and Streptococcus, even in the absence of symptoms. Bray-Curtis dissimilarities between paired samples ranged from 0 to 1, confirming substantial within-person compositional change over time. These findings suggest that assumptions drawn from cross-sectional studies-linking particular taxa or diversity values to health or disease-are not supported within individuals over time, at least in people with NLUTD due to SCI/D. Empirically characterizing normal within-person variability is a prerequisite both for interpreting urobiome results in this high-risk population and for improving the accuracy and stewardship of UTI diagnosis and treatment.