In the recent New South Wales Supreme Court decision in Williams v Burton [2026] NSWSC 486, the Court reaffirmed the importance of a plaintiff adducing probative expert evidence of the counterfactual that "a timely diagnosis would more probably than not have produced a different clinical outcome." (at [54]). 

The plaintiff, Mr Williams commenced proceedings against Dr Robert Burton (third defendant) and Associate Professor Mark Bloch (fourth defendant), alleging they negligently failed to diagnose and treat syphilis when he consulted on them in 2018. Proceedings against the first and second defendants' were resolved by earlier consent judgment.  

Mr Williams consulted Dr Burton on 30 May 2018 and Associate Professor Bloch on 13 July, 3 August and 13 August 2018. He alleged that on all those occasions he had syphilis and the doctors ought to have recognised his history, arranged appropriate testing resulting in a diagnosis and commencement of earlier treatment. He was diagnosed with syphilis at Royal North Shore Hospital on 14 November 2018.

Mr Williams claimed to have suffered injury to his left eye requiring vitrectomy, cervical spine injury, psychological and psychiatric injury, shock and general bodily and psychological trauma. 

Mr Williams was self-represented from February 2025 and at the hearing on 4 May 2026. At the hearing the defendants' made an application for judgment in their favour pursuant to rule 29.10 of the Uniform Civil Procedure Rules 2005 (NSW) (UCPR), that judgment ought to be granted in the defendants' favour because on the evidence "judgment for Mr Williams could not be supported". In determining an application under rule 29.10, the Court applies a "jury test", which requires taking the plaintiff's evidence at its highest.  

The Court determined that the defendants' owed Mr Williams a duty of care as medical practitioners "to exercise reasonable care and skill in the provision of treatment and professional advice. That duty extends to, relevantly, the examination, diagnosis and treatment of the patient." 

The Court, noting that Mr Williams was self-represented, considered "the risk of harm is better framed as the risk that his syphilis, if left untreated, would progress to a stage where it would cause serious health complications." 

On breach, the Court was prepared to accept that there was evidence capable of supporting a finding that a reasonable doctor may have undertaken more extensive STI investigations, if syphilis was present at the relevant times. 

However, Mr Williams case failed on causation.  

Central to causation, the plaintiff needed to establish that he was in fact infected with syphilis at the time of his consultations with Dr Burton and Associate Professor Bloch. The only evidence on this point was a report of Dr Baslins obtained by the defendants' but tendered by the plaintiff. That evidence was that Mr Williams likely contracted syphilis sometime after 13 July 2018.  

Therefore, the claim against Dr Burton failed because the evidence suggested that Mr Williams likely contracted syphilis after his one and only consultation with Mr Williams on 30 May 2018. 

For the purpose of assessing causation against Associate Professor Bloch, the Court accepted that Mr Williams had syphilis at the consultations on 3 August and 13 August 2018 based on Dr Braslins evidence. However, Mr Williams failed on causation because he did not establish with any expert evidence "a causal link establishing that earlier treatment would have prevented or “greatly reduced” serious complications". 

The Court determined that Mr Williams case focused on breach and that he failed to consider "the evidential burden of establishing, on a counterfactual basis, how a delayed diagnosis of syphilis by the defendants has clinically worsened his position. Without such evidence, no prima facie case exists." Thus, the defendants' application under rule 29.10 of the UCPR was successful.   

The decision highlights that causation in medical negligence cases frequently rests on the ability to prove the counterfactual scenario.  

In highlighting this issue, the Court discussed counterfactual analysis undertaken in other delay or failure to diagnose cases, including Austen v Tran [2022] ACTSC 114 (alleged delayed diagnosis of Non-Hodgkin lymphoma by a general practitioner), Alrifai v ACT [2024] ACTCA 13 (alleged delayed diagnosis of pancreatic cancer at the Canberra Hospital) and Williams v Fraser [2022] NSWCA 200 (failure to diagnose congenital pars defect by a radiologist).  

As was pointed out by the Court in Austen v Tran [2022] ACTSC 114, "working out the counter-factual obviously depends upon a degree of speculation". The lines of inquiry in properly establishing the counterfactual as evidenced in this case and those mentioned above include: 

• identifying if the condition was present at the time of the relevant consultation; 

• at the relevant consultation of the alleged breach, what investigations or steps should have been undertaken and what would have happened differently if those steps had been taken (first limb of causation); and 

• has the failure to diagnose or delay in diagnosis caused any clinical worsening or affected the prognosis (second limb of causation).  

For plaintiffs, it is clear that expert evidence must go beyond identifying shortcomings in care going to the issues of breach, to address the critical question of causation and explain what would probably have happened had reasonable care been exercised and whether this has caused any material clinical worsening. 

For defendants, the case underscores the importance of carefully scrutinising whether a plaintiff's expert evidence truly addresses the counterfactual. Where a plaintiff cannot adduce evidence capable of proving what should have occurred and when, and that earlier diagnosis or treatment would have produced a materially better outcome, there may be scope to challenge causation at an early stage. 

The decision also highlights the potential utility of applications for judgment for want of evidence under rule 29.10 of the UCPR. Although such applications are relatively uncommon, the Court demonstrated a willingness to enter judgment where a plaintiff's evidentiary case is incapable of establishing the essential element of causation. 

If you would like to discuss the implications of this decision or seek advice on defending medical negligence claims, please contact a member of our Insurance team.