A cluster of 11 cases of Listeria monocytogenes bacteremia in Kyoto, Japan.

BACKGROUND

Listeria monocytogenes infection, known as listeriosis, is relatively uncommon. However, in elderly or immunocompromised patients, it can lead to severe manifestations such as meningitis and bacteremia, making it a clinically important disease. The primary route of transmission is through ingestion of contaminated food, and since a wide range of food items may be involved, close collaboration with public health authorities is essential for effective source identification.

CASE REPORT: We encountered 11 cases of Listeria monocytogenes bacteremia within a limited region over the course of one month. Whole-genome sequencing revealed that the isolates were highly genetically related. Notably, the patients resided in different municipalities, suggesting exposure to a widely distributed food source. However, under the current Japanese legal framework, bacteremia is not a notifiable condition, which hindered timely identification of the infection source.

CONCLUSION

This case series underscores challenges in both clinical practice and the public health system in Japan, highlighting how such rare, genetically related clusters of bacteremia, occurring within a short period and across multiple municipalities, can easily be overlooked under the current surveillance framework.