On April 26, 2009, American officials declared a public health emergency after 20 cases of swine flu were confirmed in the United States. They acted in response to signs that an outbreak of swine flu in Mexico could be emerging as a global pandemic — an outbreak that had already resulted in travel bans and advisories internationally and to increasingly severe quarantine measures in Mexico.
The virus in the 20 American cases looked identical to the A (H1N1) swine flu in Mexico that at that time was believed to have killed 103 people — including 22 people whose deaths were confirmed to be from swine flu — and sickened about 1,600.
Eight of the twenty confirmed cases in the United States were diagnosed in New York City, all among students at St. Francis Preparatory School in Fresh Meadows, Queens. Officials said they had also confirmed cases in California, Kansas, Texas and Ohio. Diagnoses have also been made in Canada, Spain and New Zealand.
Top global flu experts struggled to predict how dangerous the new strain would be as it became clear that they had too little information about Mexico’s outbreak — in particular how many cases had occurred in what is thought to be a month before the outbreak was detected, and whether the virus was mutating to be more lethal, or less. American investigators noted that virtually all the cases so far in this country had been mild and urged Americans not to panic.
On April 27, the European Union’s health commissioner urged Europeans to avoid non-essential travel to the United States or Mexico. The acting director of the Centers for Disease Control and Prevention, Dr. Richard Besser, responded that the advisory was unwarranted.