The poultry industry breathed a sigh of relief after three months of testing found two Northland egg layer farms free of infectious bursal disease.
The disease attacks the immune system. It does not affect humans, but is potentially lethal in chickens.
Bursal disease, avian influenza and Newcastle disease are the most feared diseases for the New Zealand industry, which last year produced more than 87.5 million chickens.
After an outbreak of bursal disease in 1999 the Poultry Industry Association introduced a sampling regime to test every farm at least once a year.
Association executive director Michael Brooks said one such test in March threw up a false negative, which raised the spectre of a new outbreak.
Samples were sent to the National Centre for Disease Investigation in Upper Hutt, where further tests proved inconclusive.
Until there was a definitive result the association undertook control measures as if Biosecurity Act powers had been enacted.
"We took voluntary steps to put restriction on eggs and trucks going on and off the property," Brooks said.
A failed virus isolation test had to be re-performed, adding an agonising four-week wait.
Brooks said there was relief across the industry when results showed no sign of infectious bursal disease.
"There was clearly a biological cross-reaction in terms of the original testing, but it's not infectious bursal disease, so what was it?
"We're still working through that process," he said.
"I hate to think what the situation would have been if we'd had a positive."
He said the infection scare highlighted the importance of maintaining strict import controls.
"[Import] applications at the moment have to meet the requirements of the import health standard and that would require proof that potential threats from those three diseases would not arise,"he said.
"To date, people have not been able to do that."
At present only adequately processed food products and hatchery eggs are imported into New Zealand.
Hatchery eggs are isolated at secure locations and only the "grandchildren" from the original imported eggs are sold for meat and egg production.
Biosecurity New Zealand is working with an industry group to draw up a risk profile for the sector.
Dorothy Geale, senior adviser surveillance and incursion response at Biosecurity NZ, said the level of preparedness for avian bird flu was similar to that for foot and mouth.
"Looking at it from a risk-based situation they both have a very low probability of coming, but both would have a high impact," she said.
The profile aimed to identify risks associated with specific industrial sites, movement practices and methods of transmission.
"You can put a lot of money into biosecurity. It depends what you consider an appropriate level of protection for New Zealand and spend up to that point," Geale said.
"But we're in good shape for avian influenza."
In the event of a confirmed disease outbreak the industry association, the Egg Producers Federation, AgriQuality and Biosecurity NZ would co-ordinate a response.
In the case of avian influenza, other government departments would join the effort because of the associated risk to human health.
The risk profile is due to be completed next June, with recommendations on codes of practice.
Geale said the risk profile could eventually lead to legislation.
"This could be the first step," he said.
"Any programme needs to be based on science and that's what we are doing here, getting the science together."
Brooks said the industry would continue to work closely with other agencies.
"We believe it is extraordinarily important for the protection of our poultry industry and the nation's fauna that we take every step to keep these diseases out."
* 87.5 million chickens produced last year.
* 99 per cent of production consumed domestically.
* New Zealanders consumed average of 37.5kg of poultry meat last year.
* Infectious bursal disease attacks immune system of chickens; can kill them.