The attorneys for more than 5,000 people who allege that 3M’s Bair Hugger patient-warming device caused their post-surgical infections will appeal a ruling from a federal judge this week that dismissed their cases for lacking a solid scientific foundation.

Following six years of legal action and one jury trial in Minneapolis, U.S. District Judge Joan Ericksen late Wednesday dismissed more than 5,000 lawsuits against 3M, ruling that the remaining plaintiffs lacked expert evidence showing their infection theories are supported by generally accepted science. Patients in the multi-district litigation blame 3M’s machine for causing serious infections in their artificial hip or knee joints after implant surgery.

On Friday, the plaintiffs’ attorneys said that they will appeal to the 8th U.S. Circuit Court of Appeals to try to get their cases reinstated. The same court is already reviewing an appeal from the original plaintiff who lost his case against 3M in federal court in Minneapolis last year.

“The science behind plaintiffs’ claims continues to be generally accepted and reliable,” attorney Genevieve Zimmerman of Meshbesher & Spence wrote in an e-mail co-signed by several plaintiffs’ attorneys in the case. “Bacteria travel through the air on particles, and when these bacteria land on a medical implant during surgery, devastating infection can result.”

Maplewood-based 3M Co. said there is no evidence that its device causes such infections.

“The general scientific and medical community continues to reject the science behind the Plaintiffs’ theories,” 3M spokeswoman Fanna Haile-Selassie said in an e-mail Friday. “Every level of the Minnesota state courts, and now the Minnesota federal court, have rejected these claims. The FDA has also rejected them. Our industry-leading 3M Bair Hugger system has been proven to be a safe, effective and efficient method of delivering patient warming therapy.”

The Bair Hugger is used to ward off surgical hypothermia, which is relatively common without warming systems because patients are exposed to cold operating room temperatures, and anesthesia promotes loss of body heat, studies show. Postoperative hypothermia is linked to problems including blood loss, cardiac events and greater infection risks.

The plaintiffs say the Bair Hugger also promotes infections, because it includes a warming unit that sucks in ambient air from the operating room, warms it, and then blows it into a disposable inflatable blanket draped over the patient.

Although the plaintiffs draw on a wide array of peer-reviewed scientific papers, no randomized controlled trial has shown that patient-warming systems like the Bair Hugger cause post-surgical infections. Neither is there microbial evidence directly linking a specific Bair Hugger unit to any specific pathogen or joint infection.

In the absence of direct evidence, the plaintiffs have relied on observational studies like the 2011 publication in the Journal of Bone and Joint Surgery commonly referred to as the McGovern study, which purported to document a “a significant increase in deep joint infection” when the Bair Hugger was used, as compared to a competing device that uses a different method to warm patients.

Like all observational studies, the McGovern study was incapable of proving causation.

In the original trial last year involving a South Carolina plaintiff, Louis Gareis, Ericksen allowed the plaintiffs to show the jury an advanced computer simulation showing how air currents disrupted by a Bair Hugger could swirl and deposit dirty skin particles from the floor into the air above a surgical incision. That, combined with the observational conclusions in papers like McGovern, could have been enough to convince a jury that plaintiffs’ theory of infection was scientifically plausible.

But the Gareis jury sided with 3M, and 3M’s lawyers subsequently asked the judge to reconsider her earlier decision to allow the creator of the computer simulation and several other plaintiffs’ experts to testify.

On Wednesday night, she did that, ruling that four of the plaintiffs’ key witnesses including its computer-simulation expert should be disqualified from testifying. Her reasons are outlined in a ruling that is under seal.

“The impact of this order denies over 5,000 people their day in court,” Zimmerman’s e-mail said. “We will continue to digest the order, and anticipate our appeal will follow shortly.”