The Centers for Disease Control and Prevention (CDC) identified the first two A/09(H1N1) swine flu cases in California on April 17, 2009, via the Border Infectious Disease Program,[130] for a San Diego County child, and a naval research facility studying a special diagnostic test, where influenza sample from the child from Imperial County was tested.[131] By April 21, enhanced surveillance was established to search for additional cases in both California and Texas and the CDC determined that the virus strain was genetically similar to the previously known A(H1N1) swine flu circulating among pigs in the United States since about 1999.