Julia Gillard has been unable to identify the cause of a stomach bug which sparked her withdrawal from high-end talks in New York but insists she is fit ahead of an appearance on the world stage.

“All I can tell you is one other person on the travelling party got struck down by the same thing so we don’t quite know if that means we ate something the same or it’s a virus, but I’m alright now.”

The prime minister was unable to attend three of her four scheduled official engagements on Monday, including a reception hosted by United States President Barack Obama.