premise: Bird flu has aroused extraordinary concerns around the world, especially in Asia and Europe, since more than 60 people have been killed and scientists fear that the virus could be more deadly if it mutates to become transferable between humans.
  A South African newspaper reported on Thursday that migrant bird droppings collected at the Durban harbor last month tested negative for avian flu.
  So far about 4,300 samples have been collected, including 67 from migratory birds captured in Durban harbor. All the samples examined have been negative, KwaZulu-Natal provincial agricultural ministerial spokesman Vusi Zuma told the witness.
  He said the department would continue its surveillance, focusing on indigenous and commercial poultry and in some cases migratory birds.
   What occurred after migratory birds were captured in Durban Harbor?
hypothesis: become transferable between humans