The number of complaints about NSW's health care providers has doubled in the past 10 years to more than 6300 in 2016-17, in what the Opposition has described a "system at breaking point".
The Health Care Complaints Commission's annual report shows it was hit with 6319 complaints, which largely related to questionable treatments, misconduct and poor communication.
The watchdog has noticed that, increasingly, individual health practitioners are generating multiple complaints and investigations.
Fairfax Media sought further information about one mysterious practitioner in NSW who alone triggered 16 investigations in the past year, but the commission said providing further details at this point could prejudice or compromise the matters.
Only serious cases that raise a significant issue of public health or safety are referred for investigation, with just 5 per cent of all complaints deemed serious enough to be escalated last year.
"Some of the key issues and drivers were ... related to prescribing medication [and] boundary violations, assault or sexual misconduct," it said.
There are 15 individuals at the centre of 85 investigations, including the unidentified practitioner accounting for 16.
While a growing and ageing population is partly to blame for the "intensification" of complaints, commissioner Sue Dawson explained consumer expectations were being reshaped by social media.
"Complaints ... are also increasing in their complexity and diversity," the report said. "It is acknowledged there has been an unacceptable deterioration in timeliness in completing assessments and investigations."
About 16 per cent of total complaints related to public hospitals, an increase of 9.7 per cent on the previous year. Top issues were about emergency medicine, surgery and mental health care.
However, considering there were 2.8 million emergency department presentations, the number is relatively small.
The Opposition's health spokesman Walt Secord said the complaints surge indicated the NSW health system was "under enormous pressure" and "clearly at breaking point".
"Treatment constitutes the largest single source of complaints in NSW public hospitals. These are not just numbers; these are real patients with genuine concerns," he said.
"Unfortunately, doctors, nurses and other health professionals are not receiving the proper support they require to provide quality care to patients."
But Health Minister Brad Hazzard said the public hospital system, which is under his watch, accounted for less than 20 per cent of total complaints and remained among the best in the world.
He rubbished Mr Secord's statements, saying his shadow counterpart had misread the figures and his conclusions were "dead wrong".
"Overall figures are going up in every state and territory because the population is increasing," he said.
"Eighty per cent of overall complaints were about the private system, which has a bit of work to do."
The report showed complaints about nurses and midwives rose by 26 per cent.
"The majority of professional conduct complaints for nurses/midwives fall into the behaviour category, which includes complaints about nurses and midwives behaving in a manner that is perceived as rough, aggressive or intimidating," it said.
Just 2.4 per cent related to non-registered health practitioners, a group that includes cosmetic therapists, massage therapists and social workers.
In good news, the number of successful resolutions has grown to 85.2 per cent, the number of finalised investigations leapt 35.2 per cent to 330, and the commission saw a 96.2 per cent success rate in prosecutions.
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