Another important advance to ascertain the real cause of the epidemic known as TOS was the identification of the shape of the bottles containing fraudulent oil and their association with composition of the oils and bottling facilities.

Only bottles labeled “type 1”, on the left, were found to have higher chemical contamination levels as markers of the oil responsible for the epidemic. The remaining bottles fulfilled the case-definition criteria of the first case-control studies (misclassification bias), but no other sick people were reported with these other bottles.

Posada de la Paz M, Philen RM, Abaitua Borda I, et al. Toxic oil syndrome: traceback of the toxic oil and evidence for a point source epidemic. Food Chem Toxicol 1996;34(3):251-7.