2025_03_GUTAB

Background Fever is a common response in children with upper respiratory tract infections (URTIs), but its effects on gut microbiota are poorly understood. Animal studies suggest that elevated body temperature can influence gut microbial composition, immune function, and antimicrobial resistance, yet human data remain limited. Emerging evidence indicates that fever may have beneficial rather than disruptive effects. Objectives To explore gut microbiota composition during and after fever and to identify key indicators potentially moderating these microbial community shifts. Methods This study was part of the pilot phase of a randomized controlled trial (n=52) in children with acute, uncomplicated URTIs and fever (=38°C). Stool samples (n=76) from febrile children (n=39) were collected by parents during and after fever. Demographic characteristics, dietary intake, stool characteristics, and URTI symptoms were prospectively recorded using questionnaires over a 10-day period. Microbiota composition was analyzed using 16S rRNA gene sequencing and taxonomic classification. Principal component analysis and age-stratified comparisons were applied to assess group-level differences between timepoints and age groups. Bray– Curtis dissimilarity was used to quantify within-subject (ß-diversity) shifts. Results Relative abundances of Bifidobacterium spp. (20.5% vs. 15.9%), Faecalibacterium spp. (11.1% vs. 10.1%), and Bacteroides spp. (10.4% vs. 10.0%) were higher during fever than after recovery, particularly in children under 5 years of age. Principal component analysis did not confirm these differences at the group level (R² < 0.01). Bray–Curtis dissimilarity showed modest within-subject shifts (mean ßdiversity = 0.74). Dietary intake and stool characteristics were similar between sampling points, and linear regression did not identify moderating effects of predisposing factors. Conclusions In children with acute, uncomplicated URTIs and fever, gut microbiota composition showed modest, transient within-subject shifts over ten days, with higher relative abundances of potentially beneficial taxa during fever. Larger and more diverse studies with longer follow-up are needed to confirm these findings