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

<b>Introduction.</b> Typhoid fever, caused by <i>Salmonella enterica</i> 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 <i>S</i>. Typhi was diagnosed with typhoid fever. <b>Case Presentation.</b> 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 <i>S</i>. 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. <b>Conclusion.</b> 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 <i>S</i>. Typhi. This raises the urgency of transitioning from phage typing to genotyping and recommends mandatory typhoid vaccination for laboratory personnel working with <i>S</i>. Typhi to minimize infection risk.