The decision of the New South Wales Court of Appeal in King v Western Sydney Local Health Network 1 demonstrates yet again how critical the issue of causation can be in medical negligence claims. While a hospital and its medical staff were found to have breached their duty of care, they avoided a finding of liability because the plaintiff was unable to establish the necessary causal link between that breach and her severe physical and intellectual disability as a result of her mother contracting chickenpox.


The plaintiff’s mother, Mrs King, was 13 weeks pregnant when she attended Blacktown Hospital with vaginal bleeding. Mrs King told the doctor that her daughter had developed chickenpox the day before, and that she did not believe she had ever contracted chickenpox previously.

The doctor conferred with a gynaecologist and an obstetrician to discuss whether Mrs King should be administered VaricellaZoster Immunoglobulin (VZIG) to reduce the severity of maternal chickenpox and prevent infection of the foetus.  The decision was made that VZIG was not required that day, but a blood test would be carried out to check for antibodies to chickenpox, and to confirm if Mrs King had been infected. A blood sample was taken and the doctor told Mrs King that the results of the test would be discussed at her next appointment in a few days time.

At Mrs King’s next appointment, her potential chickenpox exposure was not discussed as the issue had not been recorded on her hospital record. Not long after, Mrs King was diagnosed with chickenpox by her GP. The plaintiff was born a few months later and was diagnosed with Congential Varicella Syndrome (CVS). 

Supreme Court Proceedings

The plaintiff brought proceedings in the Supreme Court alleging a breach of duty of care, which included an obligation to advise Mrs King on the availability of VZIG and its risks and benefits. 

The trial Judge found that Mrs King should have been informed about VZIG and that if she had been so informed, she would have been likely to have accepted this treatment. The hospital was found to have breached its duty of care in failing to administer VZIG. Liability then centred on whether VZIG would have prevented Mrs King contracting chickenpox. The trial judge concluded that although there was a ‘possibility’ that Mrs King would not have become infected with the chickenpox if she had been given the injection, there was insufficient evidence to make that ‘possibility’ into a ‘probability’. Accordingly, the hospital was not found to be liable in this instance.

Court of Appeal

The plaintiff appealed to the Court of Appeal however the majority dismissed the plaintiff’s application, essentially agreeing with the trial judge on the causation point, and, finding that the evidence did not establish that it was likely that the plaintiff would not have contracted CVS if the VZIG had been administered.

The majority found that the risk of Mrs King contracting chickenpox existed regardless of the hospital’s actions as she, and the plaintiff, had already been exposed to the virus before attending the hospital. It was therefore incorrect to say that the hospital’s negligent omission had increased the risk of injury. In order to establish causation, the plaintiff needed to prove that it was the hospital’s negligence that caused or materially contributed to the harm actually suffered. The plaintiff failed to establish this causal link


The fact that this was a majority decision shows how finely balanced the issue of causation can be. Nevertheless, it is often the critical factor in a successful defence of a medical negligence claim.

The case also highlights the importance of contemporaneous medical records and the weight a court gives to these records. In many cases, especially those involving unborn children, the claim will not commence until many years after the alleged negligence has occurred. Medical records will therefore be relied upon as the primary factual record. In this decision, the Court accepted the hospital and medical records in circumstances where they conflicted with the evidence of the plaintiff’s witnesses.