Biosecurity Queensland acting chief veterinary officer Rick Symons said this included the horse that had returned a positive result to one of the tests last Friday.
"We re-tested this horse and these results are negative. However, we need to wait for the results from the next round of testing in the coming weeks before we can be absolutely certain. This applies to all of the horses involved," he said.
"Eleven horses that left the affected property before the quarantine have all been traced and tested.
"The results for nine of these horses are negative, one is undergoing further testing and we are awaiting advice on the results from the final horse that was traced to New South Wales."
Two horses haved died at the Cawarral property, outside Rockhampton, as a result of Hendra infection - the first on August 7 and the second a day later.
The second death sparked an alert which resulted in the J4S Equine Nursery, and an adjoining property, being placed under quarantine.
The tests conducted so far include PCR testing, which shows any presence of the virus in the horses' blood or mucus, serological tests that indicate if any of the horses has had a reaction to the virus and is producing anti-bodies, and an Elisa test, which also scans for antibodies.
Symons said all results to date were the first stage in a series of tests to eliminate the possibility of further Hendra infections.
"I stress that further testing of the horses over the next few weeks will be required," he said.
"This is necessary as the antibodies that demonstrate previous exposure to Hendra virus take time to develop and be measured by diagnostic tests.
"The Cawarral property and a neighbouring property will remain under quarantine until such time as Biosecurity Queensland is completely confident there is no chance of any further infection. All going well, that may be in about three week's time.
"In the meantime, Biosecurity Queensland will continue to monitor all of the properties and horses concerned."
Biosecurity Queensland has engaged independent reviewer Dr Nigel Perkins to audit procedures being used as part of its ongoing response.
"This kind of independent evaluation was one of the recommendations from the Perkins Review of last year's Hendra incidents and is a proactive way of ensuring there is continuous improvement of our Hendra responses."