Probable person to person transmission of novel avian influenza A (H7N9) virus in Eastern China, 2013: epidemiological investigation.

Objective: To determine whether the novel avian influenza H7N9 virus can transmit from person to person and its efficiency.

Design: Epidemiological investigations conducted after a family cluster of two patients with avian H7N9 in March 2013.

Setting: Wuxi, Eastern China.