Jelly desserts in a fridge at Adelaide's Flinders Medical Centre have been found deliberately contaminated but no patients have been affected.
Police say a staff member came across the food, which had been contaminated with a "solid organic compound", on Tuesday morning and raised the alarm.
The desserts had been prepared for people on special non-solid diets and were due to be thrown away.
"We are satisfied that there are no patients who have been fed the contaminated foodstuffs," Acting Assistant Commissioner Joanne Shanahan said on Wednesday.
"No threat or claim has been made in connection with the discovery."
Ms Shanahan said CCTV footage had been collected and the contaminant was being forensically analysed but she could not rule out faecal matter as the source.
Southern Adelaide Local Health Network chief executive Sue O'Neill said an assessment team checked all other prepared food at the hospital in the wake of the incident but no other instances of contamination were found.
"As a precaution, we cooked all new fresh meals and personally spoke to special diet patients to ensure they had no concerns with their meals," she said.
Ms O'Neill said the object presented a threat to the patients because of its solid consistency.
"The bigger issue was probably chocking or aspiration from the contaminant," she said.