A dose of the measles mumps rubella, or MMR, vaccine. Credit:Mike Hutmacher "We are really trying to track down people who would be emerging now with symptoms, both from these two cases who travelled extensively around Melbourne, but also with the third case we need to chase up the passenger list on the flight because they were infectious on arrival in Melbourne," Dr Sutton said. "The fact that [the infected people] have been to so many places unaware of their diagnosis in a setting where people are in close contact means that we should expect more and that's why awareness of symptoms are important." The woman and the child were infectious between September 6 and September 13 and were separately at the train stations between Armadale and Southern Cross and Collins Street in the city during this period. It's believed they became infected at one of the train stations or at the St Kilda library between August 20 and September 1.

A typical measles rash. People who attended these locations between August 20 and September 1 may already be unwell with measles. The patients later walked through Chadstone shopping centre, IKEA Richmond and Ballarat. Locations where the two cases spent time while infectious between September 6 and 13 include: September 6: IKEA Richmond (11am-1pm)

September 7: Spotlight Carnegie (11.30am-12.30pm), Chadstone Shopping Centre, specifically Kmart (12pm-3.30pm)

September 8: Federation University, Ballarat (Mt Helen Campus)

September 9: Chadstone Shopping Centre (10am-1pm)

September 11-12: Frankston Train line (peak hour) – Armadale Station and Southern Cross Station

September 13: IKEA Richmond (11am-1.30pm)

The traveller returned to Australia on September 12, becoming unwell the next day. He was infectious, therefore, on the flights home and when transiting through Doha and Melbourne. These flights include one from Bucharest – flight number QR222 – departing on September 12. He stopped over for one hour in Doha, Qatar and then flew to Melbourne on QR904, arriving September 13 in the late afternoon. Health Department spokesman Bram Alexander said the Health Department was individually contacting passengers sitting in the rows ahead, behind and to the side of the man. Those who had attended a Federation University Mount Helen campus seminar with the ill woman were also being contacted. Measles is highly infectious and airborne, and can stay in the environment for up to two hours.

It has an incubation period of between seven and 18 days. Dr Sutton said symptoms of the measles included a cough, a runny nose, red eyes, followed by a high fever and then a rash that began in the face and spread down the body. He urged everyone to ensure they were vaccinated against the disease. "If those symptoms are present and you are not aware of your immunisation status or are un-vaccinated then you really need to call ahead to emergency department or GP and make sure you have a mask on while you are being assessed so that you are not putting other people at risk," he said. "Children who are too young to be immunised are obviously vulnerable until they get that vaccine at 12 months of age and a follow up vaccine at 18 months. "So if everyone else can be immunised then you don't get these cases which are imported basically from international travel."

Susceptible people who have attended these places are at risk of measles and may have the onset of symptoms anytime from September 13 until October 4. The adult woman and the traveller are both in a stable condition in hospital, while the baby is recovering at home.