A recent decision by the Seventh Circuit Court of Appeals may significantly lower the causation bar for plaintiffs in toxic tort cases. In the case C.W. & E.W. v. Textron, Inc., the Seventh Circuit was called on to evaluate a district court decision that excluded plaintiffs' experts for failing to meet the admissibility requirements of Federal Rule of Evidence 702 and Daubert v. Merrell Dow Pharmaceuticals, Inc. The Seventh Circuit's analysis of the district court's decision was relatively straightforward and the Seventh Circuit acknowledged that the district court had carefully considered the methodology employed by plaintiffs' experts. The Seventh Circuit concluded that the district court had properly exercised its gatekeeper role under Daubert in concluding that there simply was too great an analytical gap between the data and the expert opinion being offered such that the opinion amounted to nothing more than the ipse dixit of the expert.

Having affirmed the district court's decision to exclude plaintiffs' experts, the Seventh Circuit went one step further. In any toxic tort case, a plaintiff must establish both general causation and specific causation. In other words, plaintiffs must establish, through expert testimony, both that a chemical can cause the specific harm alleged and that the chemical did in fact cause the specific harm alleged. In the Textron case, plaintiffs' experts attempted, in part, to rely on what is typically referred to as a "differential diagnosis" or "differential etiology" to demonstrate both general and specific causation.  In a toxic tort case, "differential diagnosis" or "differential etiology" generally refers to a situation where an expert will consider all relevant potential causes of an illness and then eliminate alternative causes. In Textron, certain of plaintiffs' experts provided a laundry list of potential causes of plaintiffs' illnesses, including exposure to vinyl chloride, and then proceeded to exclude each of these other potential causes, leaving exposure to vinyl chloride as the only cause that could not be ruled out as having caused plaintiffs' illnesses.

The majority of courts do not allow a plaintiff to demonstrate general causation via a differential etiology. Rather, typically a plaintiff must establish general causation via reference to a scientific publication or study that demonstrates that exposure to a particular substance is capable of causing a specific disease. Here, however, in dicta, the Seventh Circuit rejected the district court's categorical exclusion of differential etiology to establish general causation. The Seventh Circuit referenced a Second Circuit decision (Ruggiero v. Warner-Lambert Co.) that noted that "there may be instances where, because of the rigor of differential diagnosis performed, the expert's training and experience, the type of illness or injury at issue . . . a differential diagnosis is sufficient to support an expert's opinion in support of both general and specific causation." Although those facts and circumstances were not present in Textron, in the Seventh Circuit, plaintiffs may now be able to demonstrate both general and specific causation without having to rely on any scientifically reliable studies that demonstrate that a particular substance can in fact cause a particular harm or illness.