Proving causation, especially in “multi-agent” and “low exposure” disease cases, with consideration too of certain COVID-19 matters

At least two attempts have been made in reported case law in the UK this year for further relaxation of the rules on causation in personal injury damages claims. Both of these attempts have failed. This insight explains why. It is first worth reminding ourselves where the law on causation, in all UK jurisdictions, had got to.

A brief summary on causation

The test traditionally applied by the UK civil courts on causation is to ask whether “but for” a particular breach of duty, the particular injury or loss would have happened. In the 20th century, two further tests were added to the “but for” one, either of which would suffice in appropriate circumstances. These were whether a particular breach made a “material contribution” to the injury or whether it meant a “material increase in risk” of the injury being sustained. The onus of proving causation on the “but for”, “material contribution”, or “material increase in risk” is on the claimant, with the standard of proof the balance of probabilities. 

In the early 21st century, the House of Lords created what has since been described as a “narrow exception to the causation requirements applicable to single agent cases” (Barker v Corus UK Ltd, House of Lords, 3 May 2006, from the speech of Lord Scott of Foscote at para. 64). They did this in Fairchild v Glenhaven Funeral Services Ltd and others, House of Lords, 20 June 2002, a case where these six conditions applied (taken from the speech of Lord Bingham of Cornhill at para. 2) - 

1. C was employed at different times and for differing periods by both A and B, and
2. A and B were both subject to a duty to take reasonable care or to take all practicable measures to prevent C inhaling asbestos dust because of the known risk that asbestos dust (if inhaled) might cause a mesothelioma, and
3. both A and B were in breach of that duty in relation to C during the periods of C's employment by each of them with the result that during both periods C inhaled excessive quantities of asbestos dust, and
4. C is found to be suffering from a mesothelioma (of the pleura - lung), and
5. any cause of C's mesothelioma other than the inhalation of asbestos dust at work can be effectively discounted, but
6. C cannot (because of the current limits of human science) prove, on the balance of probabilities, that his mesothelioma was the result of his inhaling asbestos dust during his employment by A or during his employment by B or during his employment by A and B taken together. 

The House of Lords decided in Fairchild that the law should consider causation established against both A and B when these six conditions applied. Lord Bingham of Cornhill added, at para. 34 “... I would in conclusion emphasise that my opinion is directed to cases in which each of the conditions specified in (1) - (6) of paragraph 2 above is satisfied and to no other case. It would be unrealistic to suppose that the principle here affirmed will not over time be the subject of incremental and analogical development. Cases seeking to develop the principle must be decided when and as they arise”. 

The key question for the courts in the two reported cases this year

The key, multi-faceted, question for the courts in the two reported cases this year was whether the “Fairchild exception” applied, or could be incrementally extended to apply, to situations not falling squarely within the six considerations set out above and, if so, whether that meant that causation was established in law in those situations?

Kerr and others v two Scottish local authorities, Lord Malcolm, Outer House, Court of Session, 20 December 2024

Key facts the court found established

Mrs Sarah Kerr passed away in 2022. This passing was caused by epithelioid malignant peritoneal (abdominal) mesothelioma, symptoms of which were first noted in 2020.

Mrs Kerr had worked as a chemistry and science teacher at different schools for two local authorities during various periods between 1983 and 2003. 

As a chemistry and science teacher, Mrs Kerr handled asbestos Bunsen mats, probably made of asbestos cement, especially during her early years as a teacher, with potential for Mrs Kerr to have been exposed to chrysotile, as opposed to amphibole, asbestos fibres (the former far less hazardous to health than the latter). 

Key points of law in the court’s judgment

The “Fairchild exception” did not apply in this case

In contrast to Fairchild, where exposure to asbestos was the “single agent” cause of mesothelioma of the pleura (i.e., there was no other possible causes), there were multiple potential causes of the rare abdominal mesothelioma. Epidemiological evidence was useful on this, notably “the extreme rarity of peritoneal mesotheliomas in cohorts exposed to chrysotile” and “how it is now thought that a source of inflammation or injury may be the most common explanation for the abnormal changes at a cellular level which ultimately lead to a malignancy” (para. [67] for both quotes). 

There is no proper basis for extending the “Fairchild exception” to encompass this case

As the court understood the case put forward by Mrs Kerr’s relatives “the submission came to this: if Mrs Kerr’s occupational exposure created a material risk of peritoneal mesothelioma, the special rule (i.e., the “Fairchild exception”) should be available if the true cause of the disease cannot be known”. As we will see next, no “material risk” was created on the facts of this case however “even if it had been … I see no proper basis for advancing the law in this direction” (para. [79] for all quotes). In short, it would be improper to extend the “Fairchild exception” to “multi-agent” cases (i.e., where there are other possible causes beyond asbestos). 

Even if the “Fairchild exception” applied in, or could be extended to, this case, the claim would still not succeed

On likely cumulative exposure of Mrs Kerr to asbestos “the clear weight of the expert evidence favoured ... 0.046 f/ml years” (para. [62]). “F/ml years” is the accepted measure for asbestos exposure. 0.046 f/ml years is a very low measure. So “In summary, I accept the evidence to the effect that if Mrs Kerr’s work as a teacher exposed her to any risk of developing peritoneal mesothelioma, a doubtful proposition in itself, the risk was so small as to merit disregard (sometimes referred to as being de minimis). In other words it was not material … It also follows that even if the Fairchild exception could be in play, it would not be applied in the claimants’ favour” (para. [75]). 

Edwards and others v 2 Sisters Food Group Limited, HHJ Owen, County Court at Caenarfon, 18 July 2024

Summary of facts, or assumed facts

All the claimants developed COVID-19 in or around June 2020. They were employed around that time with the defendant in a chicken processing factory. They alleged inadequate workplace safety provisions to protect them from development of the disease, also alleging that, in law, those inadequacies caused them to suffer it. 

Key points of law in the court’s judgment

The court accepted the defendant’s submission that the claimants “would only possibly be able to succeed if they were to argue successfully that any breach of duty on the part of (their employer) increased their risk of contracting COVID-19. For that to happen, they would need an extension of (the) Fairchild (exception)” (para. 17).

The court was not willing to countenance any extension in this case, explaining “COVID-19 is a virus over which an employer would not be able to exercise control in the way an employer would be able to prevent someone developing mesothelioma by ensuring that they did not come into contact with asbestos. COVID-19, in contrast to asbestos over which there can be control with proper health and safety measures in place, is a virus to which the public at large are exposed. No doubt, safety measures at the chicken processing were or should have been introduced to minimise the risk of the virus spreading but ultimately, this workforce was exposed to COVID everywhere, not just in the chicken processing plant” (para. 20). 

So, summary judgment was granted in favour of the defendant because the claimants would “face a nigh on impossible task in establishing a causal link between any breach of duty on the part of (the defendant) and their contracting COVID-19. It would require significant development of the law for any claim to succeed and such developments by courts have been strongly discouraged by the most senior courts in the land” (para. 25).

Conclusion

The decisions in both Kerr and Edwards are both first instance ones, hence susceptible to later disapproval on any appeal. It should also be remembered that “incremental and analogical development” was envisaged in Fairchild itself. The first instance decisions in both Kerr and Edwards make clear that the judges in those cases saw no room for such development in the respective situations, with the question of development not even critical to the outcome in Kerr because of the fundamental requirement of materiality of possible cause. 

On the point whether there might ever be incremental or analogical development of the Fairchild exception, it is worth stressing the closing words of Lords Neuberger and Reed in Zurich Insurance PLC UK Branch v International Energy Group Ltd, UK Supreme Court, 20 May 2015, at paras. 210 and 211 - “When the issue is potentially wide-ranging with significant and unforeseeable (especially known unknown) implications, judges may be well advised to conclude that the legislature should be better able than the courts to deal with the matter in a comprehensive and coherent way … For the courts to develop the law on a case-by-case basis, pragmatically but without any clear basis in principle, as each decision leads to a new set of problems requiring resolution at the highest level, as has happened in relation to mesothelioma claims, is not satisfactory either in terms of legal certainty or in terms of public time and money … there can be no real doubt but if Fairchild had been decided the other way, in accordance with normal common law principles, Parliament would have intervened very promptly. That may very well have been a better solution, but it can fairly be said that that observation is made with the wisdom of hindsight”.