A case of laboratory-acquired Salmonella Typhi infection due to phage typing in Japan: whole-genome sequencing confirms the source of infection.

Introduction. Typhoid fever, caused by Salmonella enterica serovar Typhi, is a systemic infection. Approximately 40 cases occur annually in Japan, most of which are imported. In August 2023, a researcher engaged in phage typing of S. Typhi was diagnosed with typhoid fever. Case Presentation. A 48-year-old man presented with high fever, diarrhoea, malaise and loss of appetite. Initial findings, including liver dysfunction and severe inflammation, led to a suspected diagnosis of autoimmune disease. However, blood cultures identified S. Typhi, confirming typhoid fever. Comparative genomic analysis demonstrated clonality between the strain handled in the laboratory and the patient isolates, indicating a laboratory-acquired infection. Conclusion. This case underscores the need for ongoing vigilance regarding the risk of laboratory-acquired infections and highlights the value of whole-genome sequencing for tracking. It would be also emphasized that this is the first reported case in Japan linked to phage typing, a conventional typing method for S. Typhi. This raises the urgency of transitioning from phage typing to genotyping and recommends mandatory typhoid vaccination for laboratory personnel working with S. Typhi to minimize infection risk.