The mother's barrister Pauline David told the court on Thursday there were a number of possibilities that could explain how the boy became infected.
Crown witness and nurse Lindie Brown, who was working at a unit manager at the ward where the boy was a patient, told the court he became "very unwell" during one of her shifts.
The court heard the boy had a temperature of 40C and began experiencing rigors – or shaking.
He was also complaining of pains in his back, stomach and head and asked for medicine to "take the pain away", the court heard.
Brown told the court she then heard the boy ask his mother "why she was doing this to him".
He then said words to the effect of "you could have put something in my cannula when I was asleep", Brown said.
During a similar incident the following day he again asked his mother why she was "doing this to me", Brown told the court.
"She [the mother] said, 'What?'" Brown said.
"And he said, 'Poisoning me'."
Brown said she made a "mental note" of the incidents and sent an email to child protection services.
Under cross-examination from David she conceded she did not make a written note about the boy's claims as it was not her duty to do so.
Brown also acknowledged the boy was in a high state of stress at the time she claims to have heard him question his mother.
She agreed with David that he displayed "considerable" behavioural problems during his stay in hospital, at times swore at nurses and was "very demanding of his mother".
"It was a battle wasn't it, the whole way?" David asked.
"It was," Brown replied.
Another nurse in the room during that same shift, Kristina White, told the court she heard the boy say something similar while "looking at" his mother.
"What have you done to my cannula this time?" White testified the boy said.
White said the mother replied words to the effect of: "Why would you say that? That makes me upset when you say those things."
David asked the witness if it was possible she misheard the boy and he actually said to his mother "don't you dare put anything in my cannula?".
"Possibly yes," White replied.
She recalled having a discussion with Brown "as soon as we left the room" where her superior made it clear she was concerned about the boy's alleged comments.
David asked both White and Brown if it was possible the boy was delirious due to the painkillers he had taken.
They were also asked if they recalled the boy saying words to the effect of "why are there elephants in the room?" around the same time he accused his mother of doing something to his cannula.
Neither woman could recall those words being said, and could not say if the boy might have been hallucinating.
Both nurses agreed he did not like medical staff putting medicine in his cannula and would "act out" towards them.
The hearing before Judge Justin Smith continues.
