Geographic Dependence, Surveillance, and Origins of the 2009 Influenza A (H1N1) Virus

Abstract

In April 2009, a new strain of human H1N1 influenza A virus was identified in Mexico. According to the World Health Organization (www.who.int/csr/don/2009_05_25), as of May 25, 2009, the virus had spread to 43 countries, with 12,515 reported cases and 91 associated deaths, and it has been assessed as having pandemic potential.¹