Spanish toxic oil syndrome: ten years after the disaster

Toxic oil syndrome (TOS), a previously undescribed disease that occurred in Spain in epidemic form in 1981, has been associated with ingestion of a reprocessed denatured rapeseed oil illegally marketed. However, the association between the syndrome and the adulterated rapeseed oil rests exclusively on epidemiological data because of the absence of toxicologic confirmation and the inability to reproduce the disease in animals. An analysis of the epidemiological evidence available on TOS is carried out in this paper, in an attempt to elucidate the aetiological role of the purported toxic oil. The adulterated oil was found to be highly statistically associated with the syndrome, such an association being extremely unlikely to be due to the effects of bias and/or confounders. The association is very strong, as the estimated relative risk shows (odds ratio = 30), and a dose-response relationship was found. Likewise, the specificity of the association is very high. The temporal sequence of events, although not entirely clear, also helps to support the hypothesis of causality. No other criterion was met, but none of these unmet criteria stands against this hypothesis. From these findings, the adulterated rapeseed oil can be considered a necessary cause for the syndrome to have occurred. Further toxicologic investigations are required to elucidate the precise toxic agent.