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Dairy products are open to E.coli contamination because of the prevalence of the bacteria in animal waste, one disease expert says.
The warning comes after dairy giant Fonterra issued an urgent recall of four of its fresh cream products last night, over fears it may contain the E.coli bacterium.
Almost 9000 bottles of Anchor and Pams branded cream, which have been distributed to shops and food service outlets across the North Island, are affected by the recall.
Fonterra Brands NZ managing director Peter McClure said the company was sorry for the inconvenience and concern the recall might cause "but food safety and quality are our top priorities".
People were advised not to use the cream, but to return it to where they bought it for a refund.
Mr McClure said signs of E-coli were discovered during standard testing yesterday morning.
The tests showed an unusually high "spike" of coli form in fresh cream and milk at Fonterra's Takanini plant in South Auckland.
Three samples were sent for independent testing, which confirmed the contamination.
"All three samples they tested at an independent lab showed positive results for E.coli," Mr McClure said.
The results were "very, very unusual".
"In the last 20-odd years we've never had an incident of E.coli in milk despite periodic spiking in coliforms."
Professor Kurt Krause, head of the biochemistry department at Otago University and director of the Webster Centre for Infectious Diseases, said there is "an awful lot of opportunity" for E.coli contamination of dairy products because the bacteria is commonly found in faeces and animal waste.
He said Fonterra still has a lot of questions to answer before the true extent of the bacteria find could be known.
"Was there a problem with the process of carrying out the normal food safety procedures and processing this cream, or was there another cause of the contamination?
"I'm thinking that cream and milk and dairy products like this are pasteurised, and pasteurisation is highly effective at reducing the counts of E.coli, which otherwise would be much more numerous. So did the pasteurisation break down, was it not pasteurised, did something in the system break down? I think we need more information from Fonterra before we can make any judgement."
Mr McClure said the cause of the contamination was being investigated and answers were expected "in a few days".
Meanwhile, Labour's primary industries spokesman Damien O'Connor hit out at the Government, saying the recall "once again tests the credibility of our food safety systems".
He said the timing of food testing and the accuracy of information provided to companies, such as Fonterra, "needs further scrutiny".
Mr O'Connor called for a stand-alone food safety agency to ensure food production "can be accurately and independently monitored".
"Fonterra is our biggest company, food production is our biggest export, and New Zealand cannot afford mistakes that can further damage our international reputation."
Affected batch numbers:
* Pams Cream 500ml - 1400684206 - best before date 21/01/2014
* Anchor Cream 500ml - 1400684207 - best before date 21/01/2014
* Anchor Cream 300ml - 1400684208 - best before date 21/01/2014
* Pams Cream 300ml - 1400684209 - best before date 21/01/2014.