Health Law Daily Wrap Up, FOOD—N.D. Ill.: General causation expert could testify in infant formula dispute where intervening cause arguments did not warrant exclusion, (May 15, 2026)

By Justin Marcus Smith, J.D.

The intervening cause issue the formula manufacturer raised was best left to the jury to decide where another expert would address specific causation.

A general causation expert’s testimony in connection with one of four infant formula bellwether cases in multidistrict litigation was relevant, fit the facts of the instant bellwether case, and would be helpful to the jury, held the federal district court in Chicago. On a prior motion to dismiss, the court had already qualified the expert and found he employed sound methods. The court now confirmed that the expert’s testimony fit the facts of the instant bellwether case. The fact that the infant in this particular matter occasionally consumed hydrolyzed formula did not render the expert’s opinion irrelevant because the infant formula manufacturer essentially raised an intervening cause argument “dressed up” as a Daubert “fit” argument. Another expert would handle specific causation issue, and the manufacturer could cross-examine that expert and make its intervening cause arguments at trial pertinent to specific causation expert testimony. It was not even clear that the instant infant would have been excluded from the clinical trial studies the general causation expert relied on for his opinion. The court accordingly denied the formula manufacturer’s Daubert motion to exclude the general causation expert (In re: Abbott Laboratories Preterm Infant Nutrition Products Liability Litigation, No. 22 C 00071 (N.D. Ill. May 12, 2026);Inman v. Mead Johnson & Company, LLC, No. 22 C 3737 (N.D. Ill. May 12, 2026)).

Background. The court previously denied a motion by infant formula manufacturer Mead Johnson to exclude the testimony of the expert in this multidistrict litigation. Mead Johnson now moved again to exclude the expert in the instant bellwether trial on the basis that his opinions did not fit the facts of this particular case.

The instant bellwether case involved an infant delivered at 29 weeks gestation. The infant weighed less than two pounds, was classified as “very premature,” and the hospital kept him in the neonatal intensive care unit (NICU). Due to concerns about a potential genetic disorder, physicians switched the infant from his mother’s breast milk to two different cow’s-milk-based hydrolyzed, hypoallergenic formulas.

After physicians ruled-out the genetic disorder, they switched the infant back to his mother’s own milk. However, about thirty days after birth, physicians switched the infant again to a formula made by Mead Johnson & Company (Mead). The infant allegedly developed necrotizing enterocolitis (NEC) and died shortly thereafter. The mother sued Mead Johnson. The parties selected this case as the fourth in an initial wave of “bellwether” trials intended to provide helpful information to the entire class of cases in this MDL.

This general causation expert, in the course of his work, was familiar with NEC and other NICU issues and had experience in epidemiological study design and analysis as a Ph.D. in Epidemiology. The consumers in this MDL retained the expert to offer a general causation opinion on the relationship between cow’s-milk-based formula (CMBF) and NEC.

The expert based his opinion on a statistical analysis in a “systematic literature review” of randomized clinical trials exploring the purported association between CMBF and NEC. The court already found the expert qualified on this issue and that he employed sound methods under the criteria of Fed. R. Evid. 702 and Daubert. The court ruled, on Mead’s prior motion to exclude, that although the expert could not opine about the threshold dose at which CMBF increases the risk of NEC, his broad analysis of clinical trial studies exploring a range of different feeding mixtures applied across the diverse feeding methods in these MDL cases.

However, the court did exclude the expert’s opinion in a different bellwether case because the infant in that matter was born at 32 weeks and weighed more than 2,000 grams. None of the studies the expert reviewed pertained to infants of that maturity, hence the court determined the expert’s opinion would not be helpful to the jury in that specific case (see Expert’s testimony did not apply to preterm infant; Abbott Labs thus entitled to summary judgment in baby formula litigation, Aug. 18, 2025).

Mead raised a similar challenge in the instant bellwether case. Mead argued the expert’s opinion was not relevant here because he was briefly fed alternative hydrolyzed, hypoallergenic formulas.

Analysis. The court found the expert’s testimony fit the instant case. The fact that the NICU occasionally fed hydrolyzed formula did not render the expert’s opinion irrelevant here. The court reasoned there was no requirement that expert testimony consider epidemiological studies that mirror the idiosyncratic circumstances of each individual infant in order to “fit” the case. Such a requirement would be impractical given the inherent difficulty of conducting any randomly controlled study. The consumer’s apparent plan to rely on the general causation opinion of this expert, together with the specific causation opinion of another expert, appeared reasonable.

Mead essentially raised an intervening cause argument “dressed up” as a Daubert “fit” argument. The court noted that intervening causes are typically the domain of specific causation witnesses. In any event, causation is typically a question for the jury. Mead would be free to cross-examine the other expert witness about specific causation and make its specific causation arguments to the jury at trial.

Exclusion of the general causation expert witness in the other bellwether case differed because the infant in that matter was born closer to term and would have been excluded from almost all of the studies relied on by the general causation expert. The general causation expert explicitly acknowledged that his opinion was “limited to infants of a certain weight and age group” because prematurity is a factor in NEC risk and “extrapolation” would be required to extend his opinion to more mature infants.

Moreover, it was not clear that the instant infant would have been excluded from the studies the general causation expert reviewed, which were based on ingestion of hypoallergenic formula while treated in the NICU. Studies of the kind the expert analyzed employed the doctrine of “intention to treat” which would not exclude infant outcomes from the researcher’s final assessment despite a change in their diets. Consequently, there was no basis for thinking that that instant infant, who would have been included in most of the studies based on his birth-weight and gestational age, would have been excluded from the researchers’ final assessments based on his temporary switch to hydrolyzed formulas.

The case is No. 22 C 3737, Master Docket No. 22 C 00071.

Judge: Pallmeyer, R.

Attorneys: Jose M. Rojas (Levin, Rojas, Camassar, and Reck, LLC) for Alexis Inman. Anthony J. Anscombe (Steptoe LLP) and Alice Greenhill (Covington & Burling LLP) for Mead Johnson & Co. LLC.

Companies: Mead Johnson & Co. LLC

Cases: CaseDecisions FoodNews FoodSafetyNews PLDrugNews IllinoisNews