Shanghai man not infected by wife

We now turn to one particular infection case which was confirmed in Shanghai on Saturday. The patient, a 56 year-old man who lost his wife to H7N9 about ten days ago, is now in a critical condition with the same virus. His case has raised concerns that the virus may become transmittable between people. But according to experts, there isn't enough evidence to suggest that human to human transmission is now possible.

Wu Fan, Director of Shanghai Disease Prevention and Control Ctr., said, "This is how we determine the existence of human to human transmission. In the latent period, the body will naturally fight the growth of the virus. In this process, the virus will only become transmittable after it grows enough to give out toxins. In most scenarios, if two cases share the same latent period, we don't usually conclude that one has passed the virus to the other."

Special report: H7N9 avian influenza