Prof Peiris posits poultry progressing problem.

Esteemed virologist Professor Malik Peiris believes the drop in H7N9 cases linked to the shutdown in wet markets, underscores the impact of the large, fast-moving and diverse poultry trade in the south east of China. 

Wet markets have closed in all affected areas and cases have subsequently dropped. Prof Peiris noted that a study of human blood samples is underway. 

This will shed light on the proportion of cases, if any, that did not have severe enough disease to put them on the hospital radar or to lift them above the "noise" of normal upper respiratory tract infections, other respiratory diseases or pollution-exacerbated lung problems. 

The new study will provide a key piece of the H7N9 puzzle.