Four out of five Victorian healthcare and aged care workers who contracted Covid-19 during the second wave did so at work, according to an analysis by the state government.

It comes as both South Australia and New South Wales relaxed their border restrictions with Victoria. SA will reinstate a 40km buffer zone for border communities from midnight on Friday, and NSW will ease restrictions next week to extend the buffer zone from 2.5km from the border to 50km, with exemptions for agricultural workers out to 100km.

Victoria recorded 148 new coronavirus cases on Tuesday and eight more people died, seven of whom were in aged care. NSW also recorded three new cases, all of known origin.

The Victorian analysis, released by the state’s chief medical officer, Prof Andrew Wilson, on Tuesday, found that 70-80% of healthcare workers who tested positive in the second wave did so at work.

He said poor infection control practices and staff working at multiple aged care facilities were key drivers of worker infection in aged care homes, while in hospitals risks were associated with outbreaks on coronavirus wards and with people removing personal protective equipment (PPE) incorrectly. Wilson said there were also outbreaks caused by how PPE was stored in aged care homes. In some cases, PPE had been contaminated by residents.

The analysis was commissioned by the health minister, Jenny Mikakos, in July. Two weeks ago, Mikakos told a Victorian parliamentary committee on Covid-19 that up to 15% of active infections among healthcare workers had been acquired at work, with the rest acquired in the community.

Wilson said that figure was likely based on the analysis of healthcare worker infections in the first wave of the virus, which peaked in late March, during which only 20% of healthcare workers contracted the virus at work.

“At the time, that was the data, that was the information that we had, that it was based largely on wave one,” he told reporters on Tuesday.

Both the state and federal governments have repeatedly pointed to community transmission when asked whether rates of infection among healthcare and aged care staff are the result of failures to supply adequate PPE in hospitals and aged care homes.

Victoria increased the supply of N95 masks to hospital workers from 50,000 per week to 800,000 per week from 1 August and later recommended that healthcare workers wear P2 masks or N95 respirators when caring for patients with Covid-19. But the Australian Medical Association said the masks were not being properly fitted.

The federal health advice, which coves aged care homes, is to wear an N95 respirator or P2 mask “when performing procedures that generate aerosols on patients with suspected or confirmed Covid-19”.

Wilson said he responded “swiftly” to concerns raised by healthcare workers.

“It’s totally understandable that workers want the best possible PPE and I would argue we are delivering that,” he said. “We’re delivering it above what other states in Australia do.”

Healthcare workers make up about 13% of all active coronavirus cases in Victoria at the moment, with 475 cases out of a total active caseload of 3,651. A further 1,530 active cases are in aged care settings.

Wilson said that “more than half” of all healthcare worker infections in the second wave were aged care workers. Among people who work at hospitals, 70% of those infected were nurses. He said those two cohorts were the most represented because there are “more of them in our [healthcare] system and they provide much closer care to their patients”.

“A lot of the people in this group are young females because that’s the predominant group we have in this setting,” he said.

Some doctors have also tested positive, as have some desk staff “who haven’t had anything to do with patients”.

In response to the analysis, Mikakos said the Victorian government would offer more online training, including additional training around the use of PPE, and conduct a trial at Northern Health around the fit-testing of N95 respirators. Fit-checking will continue to take place at other hospitals.

The government will also promote financial incentives to prevent health staff from working across different health services, and encourage doctors to use telehealth rather than going between facilities where there has been an outbreak.

Mikakos said the government would also ensure coronavirus patients were spaced out, so that only two beds in a four-bed ward were full, and provide heated marquees to act as tearooms for healthcare workers whose break facilities are not big enough to accommodate social distancing. The Victorian building authority will also conduct a safety check of basic amenities at aged care facilities.

The Victorian premier, Daniel Andrews, also addressed concerns about his plan to request an extension of the state of emergency legislation, which would extend the maximum duration of the state of emergency out to September 2021. That’s the mechanism under which rules like restricting mass gatherings and mandatory isolation for positive patients and returned travellers is enforced, although being under a state of emergency doesn’t necessarily mean stay-at-home orders are in effect.

Andrews said the state of emergency orders would still have to be renewed every four weeks – they have been rolled over six times since March.

“These restrictions will be in place for not one day longer than they need to be,” he said.