The use of epidemiological evidence in legal cases concerning delayed treatment for infection
27 October 2014
The recent decision of King v Western Sydney Local Health Network  NSWCA 162, illustrates how difficult it is for a plaintiff to prove that a health care professional has been negligent in causing them an injury for not diagnosing and treating their medical condition in a timely way even where the courts have found that the health care professional breached their duty of care.
By Damon Booth, NSW
The use of epidemiological studies to argue that earlier treatment would not have made a difference to the outcome is an effective way to defend a legal claim.
In this case, the plaintiff was a severaly brain injured child. Her mother contracted chickenpox during her pregnancy, after which the appellant developed congenital varicella syndrome (CVS). The mother had presented to Blacktown Hospital advising that she had not suffered from chickenpox previously, but that her eldest daughter might have the disease. The trial judge found sufficient evidence to persuade him that the hospital has breached its duty of care in failing to connect the mother’s complaints to likely chicken pox exposure and to prescribe varicella-zoster immunoglobin (VZIG), which would have boosted the mother’s defences to the virus.
The important issue however was whether such medication would have prevented transmission of the disease to the plaintiff in utero and subsequently, her injuries. At trial, the main evidence relied upon by the plaintiff was a German study, which was the only empirical evidence of sufficient sample size. In that study, VZIG was shown to prevent chickenpox in expectant mothers. However, the trial judge criticized the applicability of the study, noting amongst other things that the standard dosage of VZIG in Germany was almost triple that in Australia and that he could not conclude that if the mother had been given VZIG, the plaintiff would not have suffered damage. The plaintiff lost and the case went to the New South Wales Court of Appeal.
On appeal, the Court held that the risk to which the plaintiff was exposed to existed regardless of any conduct by the hospital as her mother had already been exposed to the virus through her eldest daughter. It was not correct to say that the hospital was negligent simply because there was an increased risk and that risk eventuated. The correct test was whether the failure to prescribe VZIG had materially contributed to the appellant’s risk of developing CVS. Here, no greater inference could be drawn than that the vaccine might have done something.
King demonstrates that where a wrongful act or omission results in an increased risk, the plaintiff must show that the increased risk was a necessary condition of the harm suffered. If this cannot be proven, the action will fail. It is not sufficient to establish causation to show that the risk was a mere possibility, or even that the risk eventuated. King also demonstrates how important it is to find empirical evidence that is specific to the plaintiff. This may prove difficult in cases that involve anew or novel treatment where studies regarding its effectiveness are limited in some respect. Legal cases of this type are, therefore, notoriously difficult for plaintiffs to prove and require much investigation and expert opinion evidence to be successful.