Twenty-year changes of penta-chlorodibenzofuran (PeCDF) level and symptoms in Yusho patients, using association analysis

BACKGROUND: Recently, methods for measurement of dioxins in the blood have improved. Also, techniques for analyzing large quantities of data have been developed, such as data mining. Even in subjects with elusive characteristics, it is becoming possible to find previously unknown characteristics by checking all combinations of symptoms. FINDINGS: Using association analysis of the data mining technique, we extracted and compared combinations with a strong relationship between recent symptoms (2001-2004) and recent blood PeCDF levels, and between past symptoms (1986-1989) and recent PeCDF levels, in physical, blood, dermatological, dental and ophthalmological examinations. Patients with a higher PeCDF level were more likely to present with symptoms included in the diagnostic criteria, such as pigmentation. In addition, we obtained evidence that recent PeCDF levels had a stronger relationship with recent than past symptoms. CONCLUSIONS: Recent PeCDF levels should not be compared directly with past symptoms. However, as the excretion rate of PeCDF has been constant, it is probable that PeCDF levels were higher in the past if recent PeCDF levels were also high. The study confirmed a relationship between past PeCDF levels and past clinical symptoms. For symptoms included in the diagnostic criteria, there was a stronger relationship between PeCDF levels and past symptoms than recent symptoms. Alleviation of symptoms in each patient or aging weakened the relationship between PeCDF levels and symptoms.