What is the "robust and pragmatic approach" to fact finding in relation to causation for a rare disease?

This would seem to be an appropriate case for the “robust and pragmatic approach” to fact finding in relation to causation permitted by Snell v. Farrell, supra. This rare disease can be a complication of an infected wound. It is a matter of common sense that the negligence or delay on the part of the defendants allowed the wound to reach a complicated state and lead to rapid unpredictable consequences. There is absolutely no evidence to suggest that the plaintiff would have otherwise developed this serious complication but for the negligent diagnosis and treatment by the defendants. Therefore, as a matter of common sense, I conclude that the plaintiff has established, on a balance of probabilities, that the defendants’ negligence materially contributed to the injury.