Three new farms have been found to be infected with mycoplasma bovis, in a nationwide testing programme by the Ministry for Primary Industries.
This brings the total number of infected properties with stock present to 33.
Samples are being taken from every farm in the country, with 33 properties now confirmed as having the disease.
MPI director of readiness and response Geoff Gwyn said staff didn't know what the testing would show, but did think the infection rate would be higher.
"This is good news," Mr Gwyn said.
"The fact that we have confirmed mycoplasma bovis on only three farms, and that all three of them were already on our radar, is encouraging."
Three quarters of the testing has been completed, with the remaining 19,000 out of a total of 70,000 tests to be completed by December.
The millions of dollars being spent to try and eradicate the disease is coming under scrutiny.
The testing is carried out on milk samples from every dairy farm in the country.
"It reinforces our belief that we are dealing with a single strain of mycoplasma bovis, based on the available scientific evidence and our own work in the field.
"But I don't want to take away from the fact 300 farms are under regulatory control."
Mr Gwyn also said the news would be of "cold comfort for those taking a hit for the team" on properties under restrictions in Oamaru, Ashburton, Invercargill and Hamilton.
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