Thousands of people in Victoria and Queensland may have been exposed to the highly contagious disease measles by a Melbourne man with the illness.
Health warnings have been issued in both states after it was discovered the 26-year-old from East Brunswick was in Brisbane from July 27-31 before flying home to Melbourne where he was eventually diagnosed on Saturday.
Authorities fear he may have infected others and are warning people to be on alert for symptoms.
In Brisbane, he visited Fairfield Shopping Centre, a restaurant in Sunnybank and the Brisbane domestic airport.
In Melbourne, he went to a number of public places, including the Hoyts cinema at Northland on August 1.
Queensland's chief health officer Dr Jeannette Young said large numbers of people had potentially been exposed and further measles cases could present in Brisbane or anywhere in Queensland over the next few weeks.
Queensland Health staff are contacting people known to have been in close contact with the man, who was put into isolation at the Royal Melbourne Hospital until his discharge on Wednesday.
A spokesman for Victoria's health department said passengers on the same flight from Brisbane to Melbourne had already been contacted.
Victoria's chief health officer Dr Rosemary Lester said anyone who developed the symptoms, or who knew they had been in contact with a measles case, should call their GP or hospital emergency department first.
"Measles is a highly infectious viral disease that can cause serious illness, particularly in very young children and adults," she said.
"People can develop pneumonia and other serious complications from the disease."
The illness usually begins with common cold symptoms such as fever, sore throat, red eyes and a cough, with the measles rash beginning about three to seven days later, generally on the face and then rest of the body.