Genomics of Shiga toxin-producing Escherichia coli from asymptomatic carriers in Japan highlights risk-adaptive control

Shiga toxin-producing Escherichia coli (STEC) is detected in healthy individuals, who face work restrictions to prevent secondary transmission. To assess the virulence potential, we sequence 495 STEC isolates from healthy food handlers and social welfare workers in 2021 and compare them with 250 isolates from symptomatic patients. Nineteen serotypes (e.g., O156:H25, O174:H21, O105:H7) are significantly associated with asymptomatic carriers (SAAC), while five serotypes (O157:H7, O26:H11, O111:H8, O121:H19, O145:H28) are significantly associated with symptomatic patients (SAPA). SAPA strains frequently carry major virulence factors, including the LEE-encoded type III secretion system (100%) and Shiga toxin 2a (63.2%), which are less common in SAAC strains (38.3% and 3.7%). Among the 495 carrier isolates, 35 (7.1%) are high-risk, 178 (36.0%) moderate-risk, and 282 (57.0%) low-risk based on serotype and virulence markers. These findings suggest many strains in asymptomatic carriers have limited virulence, underscoring the need for risk-based strategies that avoid unnecessary restrictions.