Assessing the Prevalence and Dynamics of Emerging Campylobacterales in Human Stool Samples in Brussels by Filtration Culture.

Thermophilic C. jejuni / coli is reported to be the first bacterial cause of gastroenteritis worldwide and the most common zoonosis in Europe. Although non- jejuni / coli Campylobacter sp. are increasingly suspected to be responsible for diarrhoea or to be involved in inflammatory bowel disease, they remain poorly isolated due to their fastidious and non-thermophilic nature. Additionally, they are not targeted by commercial syndromic PCR assays. In this study, we present routine diagnostic results over 6 years (2017-2019 and 2021-2023) of Campylobacter sp. and related species, obtained by optimised culture from 51,065 stools by both 0.65 µm pore filtration on antibiotic-free agar, incubated in an H 2 -enriched atmosphere at 37 °C (also known as the Cape Town protocol), and the use of selective inhibitory Butzler medium incubated at 42 °C. This allowed the isolation of 16 Campylobacter species, 2 Aliarcobacter species, and 2 Helicobacter species, providing a completely different view of the epidemiology of Campylobacterales, in which C. jejuni / coli represents only 30.0% of all isolates, while C. concisus represents 44.4%. C. ureolyticus , representing only 5.5% of all Campylobacterales pre-COVID-19, represented 20.6% of all strains post-COVID-19 (218% increase; p < 0.05). At the same time, the proportions of C. jejuni , C. coli , and C. concisus decreased by 37, 53, and 28%, respectively ( p < 0.05).