103 have died in Mexico, and cases are popping up across the world.
This morning the World Health Organization reported 40 confirmed cases in the U.S., double what officials have been reporting.
President Obama says it's not time to panic.
"This is obviously a cause for concern and requires a heightened state of alert, but it is not a cause for alarm," he said during a morning press appearance.
Europeans are being advised not to travel to the U.S. and the State Department is announcing today that Americans should only head to Mexico, the center of the outbreak, if absolutely necessary.
The focus now is on preventing more sickness in the U.S. and getting the word out that this year's flu shot will not protect you.
Federal officials also don't want everyone with a cough heading to emergency rooms.
"That's absolutely the wrong thing," warned Homeland Security Secretary Janet Napolitano. "We don't want to flood ERs with what we call the 'worried well.'"
The federal government has shipped 12 million doses of flu-fighting medicines to states, just in case they're needed.