 Initially called an " outbreak " , widespread H1N1 infection was first recognized in the state of Veracruz , Mexico , with evidence that the virus had been present for months before it was officially called an " epidemic " . The Mexican government closed most of Mexico City 's public and private facilities in an attempt to contain the spread of the virus ; however , it continued to spread globally , and clinics in some areas were overwhelmed by infected people . In late April the World Health Organization ( WHO ) declared its first ever " public health emergency of international concern , " or PHEIC , and in June the WHO and the U.S. CDC stopped counting cases and declared the outbreak a pandemic . 
