"MAF Biosecurity had the advantage of a test run with the Australian experience and still managed to stuff it up.
"It's a worry when an organisation like this fails to ensure a robust and accurate testing regime.
"This mistake had the potential to have a major impact on a multibillion-dollar industry.
"I am re-assured by reports that MAF Biosecurity will use the results of its internal investigation to identify ways to reduce the likelihood of cross-contamination in the future."
Initial testing had 10 quarantined horses returning positive results for equine flu,, five days after their arrival on March 23.
MAF Biosecurity animal imports team manager, Dr Rachelle Linwood, confirmed yesterday that the original samples had been retested.
"[We] are now certain that the initial positive result was due to contamination in the laboratory," she said.
"While we are very pleased that all samples have now tested negative, it is disappointing that cross-contamination occurred."
The results of an investigation into how the tests became contaminated is under way and initial findings are expected by the end of the week.
Findings from the investigation will be used to identify ways to reduce the likelihood of cross-contamination occurring in the future.