They hope to track down the source of the infection.

他们希望查出这种传染病的根源。

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The exact source of the infection for the 3 individuals is still unclear.

3例患者的具体感染来源尚不清楚。

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Veterinary experts were investigating the source of the infection, Miliband said, adding it was most likely to have come from wild birds.

兽医专家们正在就传染源进行调查。他补充说，传染源很可能来自野生鸟类。

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"It is crucial that national authorities do not rush to give information on source of infection which is not proven by bacteriological analysis, as this spreads unjustified fears in the population all over Europe, and creates problems for our food producers selling products in the EU and outside of the EU."

VOA: special.2011.06.10

Authorities have not determined the source of the infection, said Hong Kong's Chief Executive Donald Tsang.

CNN: Swine flu 'not stoppable,' World Health Organization says

In the hunt for the source of the infection, additional testing of farms is planned, said Malik Peiris, a University of Hong Kong microbiologist.

WSJ: Bird Flu Found Outside China's Mainland

Investigations are taking place to find the source of the infection, and close family of the children have been offered a vaccination as a precaution.

BBC: Four schoolchildren have hepatitis A in Swansea