Epidemiology ExpertsPlaintiff and its insurer sued a packing company, alleging breach of contract and warranties. They claimed that Defendant sold raw beef trim tainted with E. coli O157:H7, which Plaintiff then used in its ground beef products. This caused several people to become ill. The jury awarded Plaintiff $9 million in damages. On appeal, Defendant argued that the district court erred in admitting certain epidemiology experts‘ evidence.

  1. coli O157:H7 bacteria live in the digestive tracts of cows and can be transferred to meat during slaughter. Humans become infected by consuming contaminated beef, and the O157:H7 strain is so virulent that even a small dose can make a person ill. Unlike the harmless E. coli bacteria commonly found in human intestines, this strain produces toxins which result in stomach cramps and bloody diarrhea. Hemolytic uremic syndrome is a severe complication of E. coli O157:H7 infection that can cause anemia and kidney damage.

Prior to trial, Plaintiff identified as experts two professors of epidemiology who concluded that Defendant’s beef was the source of the outbreak, based on their analysis of molecular data connecting the case-patients to the outbreak, state health department records, and supply-chain traceback data. A traceback investigation starts with the case patient’s food history.

According to the pretrial written reports of the two experts, molecular data indicated that the E. coli O157:H7 likely originated from the same source. One report stated that “[b]acterial isolates that have the same DNA fingerprint are presumed to be genetically highly related and therefore from the same source.” Similarly, the second expert’s report stated that if two isolates have the same PFGE pattern, “[t]he isolates are very similar (and possibly identical) and might be derived from the same [s]ource.”

The experts cited several recent cases as evidence that Defendant was the source of the outbreak. Traceback investigations for each of those cases led to beef produced by Defendant and ruled out the other beef producers. Defendant asserted that the experts “cherry-picked” those cases and ignored others. The first epidemiology expert responded that he investigated all 54 cases and looked for epidemiological data that might link the cases together. The second expert explained that cases with incomplete information don’t always allow a traceback investigation from vehicle to source. The more complete data from Hawaii, Missouri, and New York cases allowed for the investigation to begin with the likely vehicles and to trace back to a common source, Defendant. The expert also explained that there was no apparent epidemiological link between the ignored cases and the known outbreak cases, nor had those cases undergone more discerning genetic subtyping methods.

Defendant moved in limine to exclude the experts’ testimony. The district court denied the motion, rejecting Defendant’s argument that the experts had ignored many of the cases in formulating their opinions. The district court concluded that although Plaintiff’s experts couldn’t account for every patient’s source of illness, it didn’t follow that the epidemiology experts ignored facts because they failed to account for each patient’s illness through analysis.

On appeal, Defendant argued that the district court erred in admitting the testimony of the epidemiology experts. It claimed that the methodology of the epidemiology experts was flawed because they ignored two case-patients who fell ill several days before Defendant produced the meat that allegedly contaminated the Plaintiff patties. Because these patients’ illness couldn’t be attributed to its product that was used in the Plaintiff patties, Defendant contended that the ignored cases proved that the source of the outbreak wasn’t Defendant. Its argument began with the premise that the 54 cases of on the CDC’s list shared the same source because they had indistinguishable PFGE patterns. The U.S. Court Of Appeals for the Eighth Circuit, Circuit Judge Roger L. Wollman wrote that according to the epidemiology experts, a common PFGE pattern constitutes evidence that the bacteria causing the illnesses may have derived from the same source, but E. coli O157:H7 cases that derive from different sources can have indistinguishable PFGE patterns. According to Plaintiff’s experts, the PFGE pattern must be considered along with the epidemiological information.

Judge Wollman said in his opinion that the epidemiology experts testified that they couldn’t find an epidemiological link between the ignored cases and the rest of the cases associated with the outbreak, explaining that they didn’t ignore the cases, but rather were unable to trace those cases back to their source. Reviewing the information from the 27 case-patients who hadn’t been exposed to Plaintiff patties, one of the experts testified that he tried to find a common denominator, i.e., had any of those case-patients consumed beef that could be traced back to one of Plaintiff’s four suppliers? The answer, he found, was yes, three cases—from Hawaii, Missouri, and New York—traced back to Defendant. Similarly, the other epidemiology expert explained that his traceback investigation involved all 54 cases from the CDC’s list. One of the experts testified that he had “traced back all 27 [cases not linked to Plaintiff] and ha[d] sufficient information for three of them.” He traced the cases from Hawaii, Missouri, and New York back to Defendant.

The judge held that because Defendant’s beef production on the dates in question could not have caused the two ignored cases didn’t invalidate the experts’ conclusion that the Defendant production was the source of the E. coli O157:H7 bacteria found in the Plaintiff patties. As mentioned above, the PFGE pattern identified in the outbreak was rare, but it had previously been reported to the CDC. Moreover, Defendant cited no scientific literature or expert testimony to support its argument that Plaintiff’s experts’ methodology was flawed. The district court didn’t abuse its discretion in determining that the expert evidence met the standard for admissibility and that the evidence of the ignored cases was best used for impeachment and cross-examination.

There was no error in the admission of the expert’s testimony, and the judgment was affirmed.

American Home Assurance Company v. Defendant Packing Co., 2016 U.S. App. LEXIS 6183 (Cir. 8 April 5, 2016)