U.S. Centers for Disease Control and Prevention – Emerging Infectious Diseases Journal Volume 19, Number 12—December 2013 Historic Prevalence and Distribution of Avian Influenza Virus A(H7N9) among Wild Birds Sarah H. Olson, Martin Gilbert, Ming Chu Cheng, Jonna A.K. Mazet, and Damien O. Joly   Abstract We examined 48 published studies for which sample sizes could be ascertained to determine the historic prevalence of influenza A(H7N9) virus in wild bird populations and reviewed GenBank data to further establish its distribution. Low prevalence (0.0093%) in Asia suggests > 30,000 samples would be required to detect the H7N9 subtype in wild birds.