The United States has 1,639 confirmed human A/H1N1 cases in 43 states, including two deaths, overtaking Mexico as the country having the most confirmed cases in the world, the US Centers for Disease Control and Prevention (CDC) said Friday,

The update registered a sharp increase from the case count on Thursday when confirmed cases were 896.

The CDC said because there is a backlog of likely cases that need to be confirmed through extra testing, the number of cases may jump quickly day to day as more suspected cases are confirmed.

However, the jump "does not reflect a speed-up of the epidemic," said Dave Daigle, a spokesman for the CDC. The official said as more places were now able to test for the virus, "we do expect to see the numbers climbing."

About 3.5 percent of the cases have been sick enough to be admitted to hospitals and health officials said the rate will continue to fall as more screening is done in the community.

According to the CDC, the state of Illinois has 392 confirmed cases of A/H1N1 flu, followed by 240 of Wisconsin, 174 of New York, 131 of Arizona and 107 of California.

Acting Director of the CDC Richard Besser has said they expect A/H1N1 flu to spread to all 50 states.

US President Barack Obama on Friday urged Americans to take persistent precautions on A/H1N1 flu, even though he said the virus is not as virulent as first feared.

"I want to assure everybody that we're seeing that the virus may not have been as virulent as we at first feared," Obama told a town-hall meeting with members of Hispanic communities at the White House.

"But we're not out of the woods yet. We still have to take precautions," he said.

The president said that the CDC recommends Americans to keep taking precautions.

"We may have to prepare for an even worse flu season sometime in the fall," he cautioned.

Obama also said the flu provides a chance for Americans to hold even closer together.