Clinical and Laboratory Dynamics of Bear Meat-Associated Trichinellosis in Hokkaido, Japan.

Trichinellosis is a rare infection associated with bear meat consumption found in Japan, where limited access to parasite-specific antibody testing makes definitive diagnosis challenging. In the present study, 19 patients, comprising 16 confirmed and three probable cases, treated at a tertiary care hospital in Hokkaido, Japan, during three independent outbreaks in 2018, 2019, and 2025, were retrospectively analyzed. Patients prepared brown bear meat as a roast (n = 18) or a cutlet (n = 1) and consumed it as a main dish (n = 7) or in smaller portions of a few slices (n = 12). Ten patients consumed previously frozen meat. The causative agents included Trichinella T9 and presumed Trichinella nativa. Common symptoms included rash (17/19, 89.5%), fever (13/19, 68.4%), and muscular symptoms (12/19, 63.2%). Eosinophilia (16/18, 88.9%) and creatine kinase (CK) elevation (13/18, 72.2%) were frequently observed. Creatine kinase levels were highest early in the disease course at ∼15 days post-infection and preceded the eosinophil peak, which occurred at 30 to 40 days post-infection. Parasite-specific antibody seroconversion occurred subsequently. Undercooked bear meat remains a significant risk factor for trichinellosis in this setting. The high frequency of rash, along with CK elevation preceding the eosinophil peak, may provide vital clues for this diagnosis.