High acquisition rate of extended-spectrum β-lactamase-producing Enterobacteriaceae among French military personnel on mission abroad, without evidence of inter-individual transmission

Abstract Objectives Acquisition of extended-spectrum β-lactamase-producing Enterobacteriaceae (ESBL-E) by Europeans travelling individually in high-endemicity countries is common. However, how the different ESBL-E strains circulate in groups of travellers has not been studied. We investigated ESBL-E transmission within several groups of French military personnel serving overseas for 4–6 months. Methods We conducted a prospective study among French military personnel assigned to Afghanistan, French Guiana or Cote d’Ivoire for 4–6 months. Faecal samples provided by volunteers before leaving and after returning were screened for ESBL-E isolates. ESBL Escherichia coli from each military group was characterized by repetitive element palindromic polymerase chain reaction (rep-PCR) fingerprinting followed, in the Afghanistan group, by whole-genome sequencing (WGS) if similarity was ≥97%. Results Among the 189 volunteers whose samples were negative before departure, 72 (38%) were positive after return. The highest acquisition rates were observed in the Afghanistan (29/33, 88%) and Cote d’Ivoire (39/80, 49%) groups. Acquisition rates on return from French Guiana were much lower (4/76, 5%). WGS of the 20 strains from the Afghanistan group that clustered by rep-PCR identified differences in sequence type, serotype, resistance genes and plasmid replicons. Moreover, single-nucleotide polymorphism (SNP) differences across acquired strains from a given cluster ranged from 30 to 3641, suggesting absence of direct transmission. Conclusions ESBL- E. coli acquisition was common among military personnel posted overseas. Many strains clustered by rep-PCR but differed by WGS and SNP analysis, suggesting acquisition from common external sources rather than direct person-to-person transmission.