Insecticide manufacturers held on to summary judgment as the Eight Circuit affirmed the lower court’s causation ruling under Daubert.  Junk v. Terminix International Co., No. 08-3811 (8th Cir., 12/9/10).

The plaintiffs’  home had been infested with spiders during the mother’s pregnancy, and she contacted Terminix about the problem.  Defendant thereafter sprayed a pesticide inside and outside the Junks’ home, approximately 20 times, the last occurring two years after her son’s birth. Junk alleged that the child’s multiple medical conditions were caused by exposure to ingredients in Dursban, an insecticide manufactured by Dow, distributed by Terminix.

The defendants moved to exclude the causation testimony of plaintiffs’ two medical experts, and for summary judgment.  The trial court first excluded the testimony of Dr. Richard Fenske, who had been retained to determine whether the son had been exposed to an unsafe level of the insecticide during his mother’s pregnancy and after his birth. Dr. Fenske testified that when making toxic exposure and dosage estimates he usually relied on a “deterministic modeling” method in which he creates an exposure model that accounts for numerous variables. In this case, however, he did not have sufficient data to perform such an analysis. Instead, he compared what he knew about the circumstances of the child’s exposure with those in published studies. This comparative analysis led him to conclude that plaintiff had been exposed to an unsafe level. Observing that Dr. Fenske had not followed his own usual methodology and concluding that he had relied on a number of ungrounded assumptions in his comparative approach, the district court excluded his opinion on the ground that his methodology was not sufficiently reliable.

Dr. Cynthia Bearer’s testimony was also excluded. She was a neonatologist and board certified pediatrician whom Junk retained to give her opinion on general and specific causation.  Because Dr. Bearer’s opinion on specific causation relied on Dr. Fenske’s conclusions, after the court excluded Dr. Fenske’s testimony, it found Dr. Bearer’s opinion on specific causation also lacked a scientific factual basis and declined to admit it.

Plaintiffs appealed.

The court of appeals agreed that Dr. Fenske’s comparative analysis depended on various unsupported assumptions. He did not account for differences between conditions in the Junk household and those described in the articles he consulted. In one instance, his only basis for comparison was the fact that the Junk household and those in a particular study were all treated with the Dursban ingredient chlorpyrifos. In another, he relied on a study where the only common variable between the Junks’ experience and the homes studied was the total amount of chlorpyrifos applied. Dr. Fenske thus disregarded other important variables such as where and how chlorpyrifos was applied in the household and whether the homes in a comparison study were the same size as the Junks’ home.

While Dr. Fenske was not required to produce a mathematically precise table equating levels of exposure with levels of harm, he was required to have a “scientifically valid” method to estimate that plaintiff’s exposure exceeded a safe level. The expert’s failure to follow his own general practice and his reliance on unfounded assumptions in his comparative method created “too great an analytical gap” between his opinion and the data on which it relied.

Because Dr. Bearer’s differential diagnosis depended on Dr. Fenske’s opinion on exposure, the district court did not abuse its discretion in excluding it. A differential diagnosis begins with an expert’s “ruling in” plausible causes of an injury. See Kudabeck v. Kroger Co., 338 F.3d 856, 860–61 (8th Cir. 2003). Then the expert “rules out” less likely causes until the most likely cause remains. Without a scientific basis for including unsafe chlorpyrifos exposure in her differential, her opinion amounted to speculation.

To succeed in her claims, Junk needed to present expert testimony showing that the chlorpyfiros could have caused the son’s injuries and that it did in fact cause those injuries. Junk’s  experts did not survive the district court’s Daubert analysis. After the court properly excluded Dr. Bearer’s
testimony, Junk could not prove specific causation as required under Iowa law. As there was no longer a genuine issue of material fact as to that necessary element, Dow and Terminix were entitled to judgment.