The use of private security guards in Victoria's hotel quarantine program may have contributed to COVID-19 outbreaks, an inquiry has heard.
About 99 per cent of the state's second wave of infections can be traced back to outbreaks at the Rydges on Swanston and Stamford Plaza hotels in May and June.
Department of Health and Human Services staff tasked with investigating the outbreaks found contact tracing was hampered by the nature of the security guards' work, as well as their living arrangements.
"With the benefit of hindsight, it is apparent that the use of private security guards may have contributed to the outbreaks," DHHS senior medical adviser Clare Looker said in a statement, shown to Victoria's hotel quarantine inquiry on Tuesday.
Dr Looker said many guards worked multiple jobs and lived in "crowded, dense accommodation".
"The workforce was also largely casual and so many had and were required to have more than one job to sustain themselves and/or their families," Dr Looker wrote.
"They were also a young, fit and socially active cohort and tended not to seek testing even if symptomatic until it was required on day 11 of their quarantine period."
By then, some had already passed the virus onto other household members, she wrote.
Dr Looker also found hand hygiene and the use of personal protective equipment by the guards at the hotels was "below the appropriate standard".
There was also language barriers and, at times, "a distrust or caution of government services".
"It was challenging to obtain accurate information," Dr Looker said.
Dr Simon Crouch, also a senior medical adviser to the health department, said a security guard working at the Stamford Plaza did not tell contact tracers he worked at the hotel, while guards at the Rydges lied about their living arrangements.
"In one case, the case did not disclose having a housemate. In another, the case said he lived alone in a granny flat when in fact they shared a room with someone else," he said in a statement to the inquiry.
"I understand why the cases may have not been forthcoming, but it remained a challenge and undermined our control efforts."
A hotel worker, six security guards and a nurse contracted the virus at the Rydges from a family of four returned travellers staying at the hotel in mid-May.
Genomic testing has revealed about nine in 10 of the state's second wave cases are linked to the outbreak.
It remains unclear whether the staff contracted the virus through face-to-face contact with the family or through contaminated objects, known as fomite transmission.
Dr Crouch said fomite transmission may have played a "larger role" than he initially thought.
"There is a high likelihood of fomite spread from poor cleaning products being utilised, poor PPE used by security staff, and a lack of education surrounding cleaning practice," the DHHS final outbreak management report reads.
The inquiry heard the DHHS ordered a deep clean of the hotel's common areas as soon as it was notified the first staff member had tested positive on May 26, but it was not done properly.
Staff weren't ordered into quarantine until May 30.
Dr Crouch admitted with the information he knew about the virus now, it would have made sense to quarantine staff earlier.
All workers at the Stamford Plaza were ordered to isolate on June 17, after a staff member tested positive.
"We learned from the experience of the Rydges Hotel and what we understood about the spread by acting much more quickly and decisively in the case of the Stamford outbreak," another DHHS senior medical adviser, Dr Sarah McGuiness, told the inquiry.
A total of 26 staff contracted the virus but only nine per cent of second wave cases can be linked to the hotel.
The inquiry, headed by retired Judge Jennifer Coate, continues on Thursday.