As COVID-19 lawsuits proliferate, businesses and their counsel should prepare for a battle of the experts on causation when there is no direct evidence that a plaintiff’s injury can be attributed to a certain source. As product liability lawyers know, plaintiffs typically must prove both general causation and specific causation in tort cases alleging exposure to a pathogen. General causation requires expert testimony to show that the exposure to something – here the novel coronavirus – can cause the type of injury – COVID-19 – that affected the plaintiff. Specific causation, however, requires something more. To prove specific causation, plaintiffs must be able to attribute their exposure or injury to a particular defendant.

Businesses across the country are facing challenges, including lawsuits, as they grapple with how COVID-19 has impacted their operations, work forces, and supply chains. The wave of litigation is rising, and it appears that no industry is immune. Schiff Hardin’s Coronavirus Task Force is publishing this series to identify of-the-moment issues and potential liabilities facing businesses as they begin to re-open, transform their processes, and face the new reality.

As stay-at-home orders are lifted across the country, many people will soon encounter nearly limitless vectors of exposure to the coronavirus. Businesses will need to try to pin down possible causes of plaintiffs’ diseases: was a plaintiff exposed from a family member, a friend, or a stranger? Was a plaintiff exposed at work or on the commute to work? Was a plaintiff exposed at the grocery store or at a movie theater?

Today we discuss four ways defense counsel can challenge causation.

  1. Identify Your Experts Early and Rely on Them

Businesses and their attorneys should identify consulting and testifying experts early in a case or even before lawsuits are filed. Pre-suit, consulting experts can help guide businesses through the scientific literature on COVID-19 that is developing at an astonishing pace and make informed decisions about appropriate steps to take when reopening. After a lawsuit has been filed, these experts can strategize how to effectively investigate the plaintiff’s claims and craft a discovery plan to identify all potential exposures to a plaintiff, which are vitally important in proving (and disproving) specific causation.

Businesses also should identify testifying experts early, and counsel should create a cooperative relationship with their experts at the outset of any lawsuit. No COVID-19 research existed until just a few months ago, and myriad new research is published on a weekly basis. In all cases, but particularly when scientific studies are expanding so rapidly, experts are vitally important to educate lawyers on the current state of the science.

  1. Develop Alternative Causation Theories

After a lawsuit is filed, a defendant should develop a robust factual picture of the plaintiff’s potential exposures through discovery and investigation. Essentially, businesses should use discovery to conduct “contact-tracing,” just like public health officials are doing. First and foremost, counsel should prepare to take thorough depositions of the plaintiff, family members, and other contacts to determine all possible sources of infection.

While most non-essential workers have largely stayed home for the past two months, many people will venture out as the country starts to reopen. A person staying at home has few possible exposures. But as more people commute to work, shop, gather with friends, and eventually attend public events, the risk of different exposures increases drastically. Develop a timeline of the plaintiff’s contacts. Investigate and demand discovery of the plaintiff’s social media to the extent allowed by the law and ethics rules of the jurisdiction. Once you have locked in the facts, research all of the potential exposures that the plaintiff may have encountered. Find news articles regarding these exposures and any “super-spreader” events. Identify a secondary set of non-party fact witnesses who may have more information about a plaintiff’s exposures than even the plaintiff or family members. Coronavirus initially spread at a rapid pace. As people start leaving their homes more, exposures likely will begin to increase again at a faster rate.

  1. Challenge Plaintiff’s Experts

At the outset of COVID-19 litigation, the lack of peer-reviewed research may serve as a double-edged sword. All parties may have difficulty meeting the standards required for expert testimony at trial. But the good news for businesses is that plaintiffs bear the burden of proving their case. Defendants should prepare Daubert or Frye motions, depending on the jurisdiction, to challenge plaintiffs’ causation opinions.

The Daubert standard in federal courts and the majority of state courts gives the judge gatekeeping functions regarding the scientific methodology employed by an expert. Defendants can argue that the ever-changing scientific literature relied on by plaintiff’s experts is not yet generally accepted in the scientific community. As an example, early studies reached different conclusions regarding the effectiveness of wearing face masks. But the study suggesting that masks may not be effective subsequently was retracted after other scientists questioned the reliability of its methods.  Many theories have not yet been scrutinized through the peer-review publication process. Defendants’ counsel may argue that a certain theory has not or cannot be tested, or the margin of error is too large for a jury to hear.

In many types of litigation, experts attempt to use studies for purposes beyond which they were intended. For instance, while epidemiological research may be adequate to show general causation in some circumstances, it often cannot be used to prove specific causation. Further, in addition to challenging the reliability of the scientific literature a plaintiff’s expert relies on, defendants in general should work with their own experts to ensure the opposing side is not stretching the meaning of a study beyond recognition. Defendants can often limit the issues for trial or more efficiently resolve a case by effectively using pre-trial Daubert/Frye motion practice.

  1. Keep an Eye on the Law When You Prepare for and Try the Case

Defendants should consider how to move in limine or prepare objection strategies to make sure that a jury hears only expert testimony that is admissible. As all trial lawyers know, cases can be won or lost based on what evidence the judge allows in. On the legal front, defendants must be intimately familiar with the causation standards in their jurisdiction. The trial lawyers also must keep the jury instructions at the forefront of their minds, making sure that the evidence fits the instruction and challenging improper expert testimony.

As an example, in some jurisdictions, a plaintiff must prove that exposure to a substance was a “substantial factor” in causing an injury. In toxic tort litigation, plaintiffs’ experts sometimes attempt to stretch specific causation beyond the scientific literature and opine that de minimis exposure was a “substantial factor” in the plaintiff’s injury. But some courts have pushed back. For instance, in the asbestos litigation, the high courts in Ohio,[1] Texas,[2] Virginia,[3] and Pennsylvania[4] have limited expert testimony offered by plaintiffs that fleeting exposure may have been a significant factor in causing disease. This is particularly noteworthy given some early COVID-19 research that indicates patients with a higher viral load, or dose, of the novel coronavirus may suffer from more severe symptoms of COVID-19.

Needless to say, the science will pose a challenge for all parties as COVID-19 litigation gets underway. Business counsel must pay close attention to the most recent studies, proactively work with their experts, and develop thoughtful and strategic approaches to challenging causation opinions that are not supported by the medical literature.


[1] Schwartz v. Honeywell International, Inc., 153 Ohio St.3d 175 (Oh. 2018).

[2] Bostic v. Georgia-Pacific Corp., 439 S.W.3d 332, 338-42 (Tex. 2014)

[3] Ford Motor Co. v. Boomer, 285 Va. 141, 156-60 (Va. 2013).

[4] Betz v. Pneumo Abex, LLC, 615 Pa. 504, 549-54 (Pa. 2012).