It is trite law to say that a doctor owes a duty of care to his or her patient. Australian courts have repeatedly said that this duty is inherent to the doctor/patient relationship. The duty was described by the High Court of Australia in Rogers v Whitaker (1992) 175 CLR 479 at 483:
"The law imposes on a medical practitioner a duty to exercise reasonable care and skill in the provision of professional advice and treatment. That duty is a "single comprehensive duty covering all the ways in which a doctor is called upon to exercise his skill and judgment"; it extends to the examination, diagnosis and treatment of the patient and the provision of information in an appropriate case".
A more difficult question is whether a doctor owes a duty of care to third parties who are not patients, but who might conceivably be affected by the doctor's treatment of a patient. To date, it appears that the Australian courts have refused to acknowledge that such a duty exists, except in exceptional circumstances where a doctor might conceivably be liable to a third party who has a relationship with the patient and who is at foreseeable risk of injury because of the patient's medical condition.
Circumstances where doctors have been held to owe duties to third parties
The courts have carved out specific situations where a doctor can, with lawful excuse, disclose his patient's health information to third parties or the public at large.It must however be remembered that these situations are part of a class of exceptions. They do not give rise to a duty of care owed by a doctor to third parties.
BT v Oei  NSWSC 1082
AT presented himself to the defendant Oei, a medical practitioner, on numerous occasions between November 1991 and January 1993. AT complained of feeling unwell and suffering from a variety of ill symptoms. It was alleged, on behalf of the estate of AT, that Oei was negligent in failing to diagnose AT with HIV, and sought general damages for psychiatric injury and/or nervous shock suffered by AT upon learning that he had infected his wife, BT, with HIV.
In addition to the claim brought on behalf of the estate of AT, BT brought her own claim against the defendant. She alleged that the defendant owed her a duty of care, and that he breached that duty in failing to diagnose her late husband. She contended that the content of the alleged duty was to diagnose AT's HIV infection and/or to give proper counselling and advice to AT as to the need for an HIV test. BT claimed that she was "within the class of persons who were at risk of foreseeable injury if the defendant failed to properly counsel and advise AT to have an HIV test".
The defendant argued that, as a doctor, he owed a duty of care to AT only. He conceded that a sexual partner of AT was a person at risk of foreseeable injury, but argued that BT needed to prove something more than this to successfully establish that he owed her a duty of care. As the court observed, it is difficult to identify precisely what that something else may be.
Ultimately Justice Bell found that Oei did owe a duty of care to BT. Justice Bell said that she arrived at this conclusion after taking into consideration "public policy reflected in the statutory obligations placed upon medical practitioners with respect to the treatment of and supply of information to patients with sexually transmissible medical conditions", as well as the following additional matters:
"There is no conflict between the duty owed by the defendant to AT and BT as the two are coincident;
BT was a sexual partner of AT;
It was reasonably foreseeable that AT, if HIV positive, would transmit the virus to a sexual partner;
AT was unaware of his HIV status (in this respect the condition was latent);
The defendant's specialist knowledge and training equipped him to identify the risk that AT had contracted HIV;
Failure to diagnose and adequately counsel AT to undertake an HIV antibody test exposed AT's sexual partner/s to the real risk of contracting a fatal disease."
In addition, Justice Bell said that the nature and content of Oei's duty to AT, and by extension to BT, was as set out in Rogers v Whitaker (1992): "It is to exercise the reasonable care and skill expected of a general practitioner in 1992… In this case expert evidence as to the practice of general practitioners in 1992 plays an influential role in ascertaining the standard demanded by the law".
PD v Harvey  NSWSC 487
Where a patient and his partner attend the same consultation with a doctor, and arrange together for STD or HIV testing, the doctor is required to inform both the patient and his partner of his results, and vice versa. In PD v Harvey, the plaintiff and her then future husband, FH, who was from Ghana, attended a joint consultation with the defendant, Dr Harvey, for the purpose of having blood tests to determine if either of them carried the HIV virus or other STDs. The defendant notified only FH of his positive HIV status. The plaintiff later contracted the HIV virus, and successfully brought an action in negligence against the defendant. A subsequent appeal by the defendant to the New South Wales Court of Appeal in Harvey v PD (2004) 59 NSWLR 639 was unsuccessful.
AAA v BBB  WASC 139
Mrs AAA retained BBB to provide professional counselling services to her in respect of relationship difficulties between her and her husband, Mr AAA. It was said that BBB commenced a sexual relationship with Mrs AAA which led to the breakdown of Mr AAA's marriage. Mr AAA alleged that BBB breached the duty of care he owed to Mrs AAA in that he failed to act in a professional manner and allowed a conflict of duty to arise as he encouraged, induced and commenced a sexual relationship with Mrs AAA. Mr AAA said that BBB's breach of duty to Mrs AAA "caused or substantially contributed to" the breakdown of his marriage. Mr AAA sought to recover damages from BBB, as well as the medical practice which employed BBB upon the basis that the medical practice was vicariously liable for the conduct of its employee, in respect of economic loss allegedly suffered as a consequence of breaches of the duty of care he owed to Mrs AAA.
The question which came before Justice Hasluck was whether this fact scenario gave rise to a duty of care not only to Mrs AAA but also to Mr AAA. Justice Hasluck found that it did not - there was nothing in the contractual relationship comprising the retainer which obliged BBB to give consideration to the position of Mr AAA. Justice Hasluck said that the duty owed by BBB to Mrs AAA "cannot readily be regarded as coincidental with duties owed to the plaintiff of the kind contended".
Generally speaking, a doctor does not owe a duty of care to third parties. The courts have however recognised that in specific situations a doctor might, with lawful excuse, disclose his patient's health information to third parties or the public at large. Sexually transmitted diseases might arguably be one such exceptional category.
In the words of Justice Hasluck in AAA v BBB, "A medical practitioner treating a patient in respect of a sexually transmitted disease might conceivably be liable to a sexual partner of the patient if such a person is foreseeably at risk of injury but that would be because there is no conflict between the duty owed to the patient and the obligation to the person at risk".