Wilsher v Essex Area Health Authority

A claimant in negligence bears the burden of proving, on the balance of probabilities, that the defendant’s breach caused or materially contributed to the injury. Proof that a breach merely increased the risk of injury does not reverse that burden.

A material increase in risk may support a common-sense inference of causation where the innocent and culpable exposures operate cumulatively through the same causal agent. That reasoning does not establish causation where the breach exposed the claimant to only one of several distinct agents, any one of which might independently have caused the injury.

A very premature infant developed retrolental fibroplasia, causing serious visual impairment. He claimed that hospital staff had negligently administered excessive oxygen. The trial judge found negligence and awarded damages after placing on the health authority the burden of showing that its breaches had not caused the condition.

The Court of Appeal, by a majority, affirmed the award: [1987] 1 Q.B. 730. It upheld one finding of negligence but rejected the trial judge’s other findings of breach. The central issue before the House was whether the remaining negligence had been proved to have caused or materially contributed to the condition, or whether a material increase in risk was sufficient.

1. Appeal allowed unanimously. Lord Bridge of Harwich delivered the leading speech. Lord Fraser of Tullybelton, Lord Lowry, Lord Griffiths and Lord Ackner agreed with it and with the proposed order.

2. Per Lord Bridge, the claimant bears the burden of proving on the balance of probabilities that a breach of duty caused or materially contributed to the injury. Bonnington Castings Ltd v Wardlaw [1956] AC 613 authoritatively rejected any general rule reversing that burden merely because the injury was of a kind against which the duty was intended to protect.

3. Per Lord Bridge, McGhee v National Coal Board [1973] 1 WLR 1 created no new rule of law and did not reverse the burden of proving causation. The majority there drew a robust, common-sense inference from the primary facts that successive periods of exposure to the same causal agent had contributed cumulatively to the disease. Lord Wilberforce’s reasoning suggesting that the creator of the risk bore the burden of disproving causation represented a minority view.

4. Per Lord Bridge, that reasoning could not determine the present case. Excess oxygen was only one among several distinct possible agents capable of causing retrolental fibroplasia. Failure to guard against one possible agent supplied no evidence or presumption that it, rather than another possible agent, caused the injury.

5. Per Lord Bridge, the trial judge had decided causation on the erroneous premise that the authority bore the burden of disproving it. His reasons did not show that he would otherwise have found causation proved. The sharply conflicting expert evidence could not properly be resolved by the House from the transcript.

6. Per Lord Bridge, an appellate court should exercise particular caution before resolving complex technical conflicts between experts which the trial judge has left unresolved. The order of the Court of Appeal and the trial order were set aside, save as to costs. The causation issue was remitted to the Queen’s Bench Division for retrial before a different judge with an open mind.

1. House of Lords: The appeal was allowed unanimously. The orders below were set aside, save as to costs, and the causation issue was remitted for retrial before a different judge.
2. Court of Appeal: By a majority, the court affirmed the damages judgment: [1987] 1 Q.B. 730. It unanimously upheld negligence concerning the misplaced catheter but reversed the other findings of negligence.
3. Queen’s Bench Division: Peter Pain J found the health authority liable and awarded the claimant £116,199.14. He treated the authority as bearing the burden of proving that its negligence had not caused or materially contributed to the injury.