The parents of a Brisbane boy whose flu led to a blood infection are warning other families how sepsis can kill healthy children in just hours.
The illness has also caused organ shutdown in a Mackay teenager also battling the flu.
Now Queensland doctors are hoping to diagnose the infection faster with a simple test.
In July, 12-year-old Caleb Logan complained of a sore throat, so his mother Rachel took him to the doctor.
The doctor said he had a viral infection and to come back if he was feeling any worse.
Days later, Caleb needed a machine to breathe.
"I was so scared, I was terrified," Caleb said of his sudden deterioration.
He was diagnosed with influenza B and sepsis, which causes organs to shut down, and was put in an induced coma.
"We had to prepare ourselves that the next 24 to 48 hours was critical and he may not make it through the night," his mother said.
It is an almost identical story to Mackay teenager Mercedes King, whose condition at Lady Cilento Children's Hospital has now been revised from critical to stable.
Caleb's doctor is spearheading a landmark Queensland study, hoping to develop a simple blood test that could prove to be a game-changer for other children.
The test could determine who has sepsis and who is likely to develop it within a 12 to 24 hour period.
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Sepsis develops when the chemicals the immune system releases into the bloodstream to fight an infection cause inflammation throughout the entire body instead.
With symptoms mirroring the flu, study hopes genetic markers will identify why otherwise healthy children's bodies attack themselves.