Victorian Health Minister Martin Foley says authorities believe there is a "minimal" risk workers at a drive-through COVID-19 testing site in Melbourne's west were exposed to the virus, after a traffic controller tested positive this morning. Mr Foley said the worker from the Moonee Valley Racecourse testing site developed symptoms on Monday evening before getting tested on Tuesday and returning a positive result this morning. He said contact tracing interviews were underway, but the worker had not been linked to the current outbreak as a primary close contact. Some tier 2 exposure sites have been listed for the new case and a number of household and social contacts are isolating and undergoing testing. "Prior to their tests ... they worked at least two days whilst infectious," he said. "We do believe that there will be minimal risk to those at the site ... however, the site has been closed, all the staff who have worked on the same shifts have been sent home to isolate and to be followed up and our pathology team are identifying in fact whether there were any positive cases who went through that testing centre during the period in which that person worked." Chief Health Officer Brett Sutton said the infection was a concern and authorities were in the early stages of understanding how the worker caught the virus. "At a testing site, obviously that's a point we'll look at, in terms of how he might have acquired it, but we have to go through that process of interviewing, understand where he's been while potentially infectious and then really work out what the links might be," he said. Professor Sutton said most people going through the testing site would not be winding down their window to speak to the traffic controller and so were unlikely to be at risk. "I think it's more about where he's acquired it from rather than the risk to those coming through," he said. The testing site worker case is on top of eight new locally acquired cases of COVID-19, detected on Tuesday, all of which had been in quarantine throughout their infectious period.