The girl died in a Melbourne hospital over the weekend after six weeks in intensive care battling rare complications of a bacterial infection known as Shiga toxin-producing E.coli (STEC).
The rare but serious infection releases toxins into the body, inflaming blood vessels and causing clots which can produce gastro symptoms and damage the kidneys and other organs.
Sassi's family said they had "been living a nightmare" after the infection led to Haemolytic-uraemic syndrome, or HUS, which left the child with kidney failure and a brain injury.
"We've lost our darling girl," the Salter family wrote in a GoFundMe post.
"Sassi was strong. Surprising many at each corner. She was courageous and a fighter. She fought so hard. We all fought so hard."
Her parents believe she might have contracted STEC during a trip to a petting zoo in July where she held, rode and petted farm animals, which commonly carry the infection in their guts.
A second child with a confirmed case of HUS became sick after visiting the petting farm in May.
Despite a thorough public health investigation, Victoria's Deputy Chief Health Officer Clare Looker said officials had been unable to definitively link the farm to the infections.
The petting zoo in question was fully compliant with public health measures, which includes ensuring appropriate handwashing facilities and hand hygiene signage, Dr Looker said.
"We know this bacteria exists in many farm animals, so I don't think that shutting a single farm, that is taking all the right pubic health protective measures, wouldn't stop the risk for children," she said.
"Hand washing after touching animals, using the bathroom and preparing or eating food is the best way to protect yourself from STEC infection."
The two children are the only known cases of HUS in Victoria in 2026, while STEC has been confirmed in 179 across the state.
Across Australia, about 1000 STEC infections are reported in Australia each year, of which a very small number of these people develop HUS, the Australian Centre for Disease Control says.
STEC is transmissible through contact with animals and their faeces and contaminated foods and environments.
Children under five years of age, immunocompromised people and those aged over 65 are at greatest risk of developing the infection.
People should avoid consuming undercooked meat, unpasteurised milk or juice, unwashed salad ingredients and untreated water, which can all carry STEC, Dr Looker said.
Symptoms of the infection include bloody diarrhoea, nausea, vomiting, fever, dehydration, seizures, jaundice and hypertension.
"Fortunately most people do fully recover from STEC and even if they go on to develop HUS, most commonly people make a full recovery," Dr Looker said.
More than $50,000 has been raised to support the Salter family, which they said "allowed us to spend every second at Sassi's side".
"There are no official treatments as such for HUS. The treatment is about supporting the body and time," they wrote.
"Please donate blood if you're in a position to do so. This is a lifeline for many critically ill people."
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