[Tetrodotoxin Intoxications in Nagasaki, Japan: Symptoms of Patients, Tetrodotoxin Levels in Leftover Food and Clinical Urine and Serum Samples].

Incidents of food poisoning associated with tetrodotoxin (TTX) contamination occur every year throughout Japan. Here, we determined TTX levels in leftover foods and serum and urine samples from eight food poisoning incidents associated with TTX contamination in Nagasaki, Japan, from 2011 to 2017.Seven food samples associated with four of these food poisoning incidents were classified as weakly toxic (four samples), moderate-to-strongly toxic (two samples), and strongly toxic (one sample).In comparison with previous reports, TTX was detected at harmful levels in the urine samples, but the grade of poisoning symptoms varied.The patients' time to maximum serum TTX levels (T_max) was estimated to be 12-24 h after ingestion of TTX-containing foods. Additionally, serum TTX levels of 19.5 ng/mL or higher within 24 h after ingestion indicated Grade 3 poisoning associated with respiratory abnormalities.These conditions were considered indicators of severe symptoms, while TTX levels of 1-3 ng/mL relate to the onset and disappearance of symptoms. A negative correlation was found between the logarithm of serum TTX concentration and the time after ingestion for two patients, indicating that the TTX serum levels decreased logarithmically. Furthermore, the TTX serum half-lives (T_1/2) were 17.5 and 23.7 h.The results of this study enhance our understanding of TTX food safety and contribute to TTX risk assessment.