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8th Circuit Clarifies Admissibility of Medical Differential Diagnosis Testimony Under Daubert

On June 8, 2014, the 8th Circuit reversed a lower court ruling excluding medical causation testimony under Daubert in Johnson v. Mead Johnson & Co.  In doing so, the 8th Circuit clarified the trial court’s role in determining admissibility of medical differential diagnosis testimony under Daubert, finding the medical testimony admissible even though it failed to conclusively rule out some other potential sources of infection.

Johnson sued Mead & Johnson, the maker of Enfamil, claiming that his baby had suffered brain damage from a C. sak infection allegedly contracted from contaminated formula.  Johnson presented 3 medical causation experts who used a differential diagnosis to conclude that the formula was the most likely source of the infection.  In doing so, the experts had done a genetic test which matched the strain of bacteria found in the plaintiff’s baby to a strain found in other infants who were known to have ingested the same formula.  

On defendant’s motion, the trial court excluded the testimony of all of the experts under Daubert, finding that the experts had not used reliable methodologies in failing to reliably rule out other causes of the C. sak contamination. 

The 8th circuit reversed, finding that the experts had reliably “ruled in” the formula as a potential cause of the C. sak infection, thus the underlying premise of the claim was scientifically valid.  The court further reasoned that “experts are not required to rule out all possible causes when performing the differential etiology analysis,” and that “a differential expert opinion can be reliable even ‘with less than full information.’”  The 8th Circuit instead found that these factors went to weight and not admissibility, and that the expert testimony was “within the range where experts might reasonably differ.”

It will be interesting to see if this case is extended beyond the medical causation realm into other areas of causation testimony. 

© Copyright 2020 Armstrong Teasdale LLP. All rights reserved National Law Review, Volume IV, Number 171
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About this Author

Derick E. Allen, Intellectual Property lawyer, Armstrong Teasdale law firm
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As a registered patent attorney and partner in the firm’s Intellectual Property practice group, Derick Allen assists both emerging and Fortune 500 pharmaceutical, chemical and life science-based companies with the development and application of their technologies. In view of the diverse nature of the companies Derick serves, he has developed a practical, cost-effective and business-oriented approach to secure and protect their intellectual property rights.

Derick has experience in advising such companies in the strategic development and...

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