It took more than a week for the Cedar Meats abattoir to give Victorian health authorities a full list of workers potentially exposed to COVID-19 during the state's first wave.
A parliamentary inquiry wants law changes considered to help improve contact tracing for public health emergencies.
Current laws mean someone's health information can't be disclosed without their express permission.
This hindered health officials in letting Cedar Meats staff at Brooklyn know they may have been exposed to the virus during the first wave, the report tabled in parliament on Tuesday said.
The first case was identified on April 24, and another two days later.
On the 27th, the health department told Cedar Meats the cases were linked and it was investigating a potential cluster at the abattoir.
Employees considered close contacts of the duo were prioritised.
But information allowing for comprehensive contact tracing of all staff and visitors wasn't handed over to the health department until May 4.
By late May, 111 cases were linked to Cedar Meats.
The Australian Medical Association told the inquiry multiple GPs had been aware of the abattoir outbreak before it was publicly announced because of workers coming in for testing.
Better communication with GPs at the outset could have helped reduce the severity of the cluster, the association said.
Victoria's opposition said Tuesday's interim report could not be trusted because the Public Accounts and Estimates Committee that produced it was dominated by Labor MPs.
Australian Associated Press