To expand on Rod's answer, under section 79 of the NSW Public Health Act 2010 "Duties of persons in relation to sexually transmissible diseases or conditions", a person "is required to take reasonable precautions against spreading the disease or condition". The penalty is pretty serious at 6 months imprisonment and/or $11,000 fine, which has made this amendment very controversial because many people believe that it now sends mixed messages.
So while notification is no longer required under the Public Health Act, as Rod pointed out, it is an offence under the Crimes Act to infect someone.
This was emphasised in a High Court ruling in 2017 that overturned long standing precedents regarding "grievous bodily harm" and the meaning of "malicious". The new precedents set in the case are significant:
1. "Grievous bodily harm" is no longer limited to an "immediately recognisable" harm to the body. It now includes an infection that manifests at a later date.
2. "Malicious" is no longer limited to knowing that something "would probably happen". It now includes knowing that something "could possibly happen". For STI's, this means that simply having prior knowledge of the infection is enough to satisfy the meaning of "malicious" for the purpose of the Crimes Act.
You can read about the ruling here:
Aubrey v The Queen
There are however several points to note about the case and amendments to the NSW Crimes Act:
1. It's my understanding that the accused in this case didn't just fail to inform the other party that he was infected, but actually told them that he wasn't infected. (The STI in this case was HIV and he was sentenced to 5 years imprisonment.)
2. Section 36 of the NSW Crimes Act "Causing a grievous bodily disease" (which was one of the original offences in the case) was repealed sometime between the original case being heard and the High Court Appeal. The details about this are as follows:
Crimes Amendment Act 2007 No 38:
[1] Section 4 Definitions
Insert at the end of the definition of Grievous bodily harm in section 4 (1):
, and
(c) any grievous bodily disease (in which case a reference to the infliction of grievous bodily harm includes a reference to causing a person to contract a grievous bodily disease).
Explanatory note
The amendment extends the definition to make it clear that causing harm to a person includes causing a person to contract a disease. As a consequence, item [9] omits the separate offence under section 36.
...
[9] Section 36 Causing a grievous bodily disease
Omit the section.
Explanatory note
This item omits the offence as a result of the extension of the meaning of “grievous bodily harm” by item [1] to cover diseases and the consequent extension of the offence under section 33 of inflicting grievous bodily harm.
3. The same Amending Act also removed the definition of "Maliciously", thereby removing the concept of "malicious conduct" from the Crimes Act. Occurances of the word "maliciously" were replaced with the words "intentionally or recklessly" for many offences. The details about this are as follows:
Crimes Amendment Act 2007 No 38:
[2] Section 5 Maliciously
Omit the section.
Explanatory note
This section (which defines “malicious” for the purposes of offences under the Act) is being repealed as a result of the replacement of that term in offences under the Act with the modern fault element of “intention” or “recklessness”.
[3]
(a whole bunch of sections listed here...)
Omit “maliciously” wherever occurring.
Insert instead “intentionally or recklessly”.
Explanatory note
This item makes consequential amendments on the omission of the concept of “malicious” by item [2].
Given the amendments, time will tell how the High Court ruling in regard to "malicious conduct" applies to the newer concept of "recklessness". I would think that when tested, the result would likely be the same, in that not disclosing something that is known would constitute "reckless indifference" in the newer terminology.