A fourth child is being treated for the potentially deadly meningococcal disease in Brisbane.
The boy was admitted to Lady Cilento Children's Hospital on December 31, a day before three other children from the same family were taken to the same hospital with the disease.
All are in a stable condition and expected to recover.
Queensland Health says the cases are unrelated and there is no cause for alarm about a possible meningococcal outbreak.
"You need to be a close contact to be at increased risk of meningococcal disease and that does not include being in the same sort of general area as a case," physician Dr Megan Young told reporters on Wednesday.
The three children admitted on New Year's Day were all believed to be aged under five and hail from Brisbane's northside.
They tested positive for meningococcal after spending New Year's Eve with family at the popular South Bank Parklands celebrations but are believed to have become ill after an extended family gathering over the holidays.
All those identified as having close contact with the children had been contacted and provided with antibiotics where appropriate, Dr Young said.
She said meningococcal sufferers typically spent a few days in hospital although that depended on the extent of their condition.
Meningococcal is a severe but uncommon infection that occurs when meningococcal bacteria invade the body from the throat or nose.
Close and prolonged contact with a person who has the bacteria in their nose or throat is usually needed for the bacteria to spread to others.
Symptoms in young children include fever, refusal to feed, irritability, grunting or moaning, extreme tiredness or floppiness, nausea or vomiting, diarrhoea, turning away from light, convulsions and rash of red or purple pinprick spots or larger bruises.
