WASHINGTON - The United States has confirmed 160 cases of the A(H1N1) influenza virus in 21 US states, the Centers for Disease Control and Prevention said Saturday.

Most of the cases were mild, said Anne Schuchat, the CDC's interim deputy director for science and public health programs. Thirteen of the confirmed cases were hospitalized.

One death has been confirmed so far in the United States, a Mexican toddler visiting relatives in Texas.

But despite reports that the outbreak in Mexico may be stabilizing, Schuchat struck a cautious tone, warning that: "We can't afford to let down our vigilance.

"We have information that this novel virus continues to spread with increasing cases and increasing states affected. And we are acting, as President Obama said this morning, actively and aggressively," she told a news conference.

"I will not be surprised if we find additional cases or additional deaths," she warned.

President Barack Obama said in his weekly radio and Internet address that he "would sooner take action now than hesitate and face graver consequences later."

The Obama administration has taken preventative measures, including delivering a quarter of the 50-million-dose national stockpile of the antiviral drugs Tamiflu and Relenza.

Obama has also asked Congress for 1.5 billion dollars to purchase additional antivirals, emergency equipment and fund the development of a vaccine that can prevent the virus.

About a third of the US cases have had contact with Mexico, which has been at the epicenter of the outbreak, with 16 dead and a total of 427 cases of infection.

"The important point is the majority of cases don't have direct contact with Mexico, they didn't travel to Mexico," Schuchat said.

"It is much more likely that people are getting this particular infection now from somebody within their own communities. We do think there is sustained transmission here in the US in several areas," she said.

She said the median age of cases was 17 years old, with people infected ranging from one to 81 years old and a majority of the cases younger than 20.
Health authorities were still attempting to determine the severity of the outbreak in the United States, according to Schuchat.

Officials have urged common-sense steps such as frequent, careful hand-washing, and said sick people should avoid travel -- but urged the healthy population not to shun restaurants, airplanes or other crowded areas.

Her comments came as the World Health Organization (WHO) indicated it was still trying to determine the severity of the new virus in Mexico.

"Severity is not completely established," said Mike Ryan, WHO Director of Global Alert and Response, adding that it was still not clear how severe or mild the virus was.

A full blown global pandemic could be declared if the virus managed to spread within countries on a continent other than the Americas, where the outbreak originated.

"At the present time, I would still propose that a pandemic is imminent because we see the disease spread," said Ryan. But he stressed that there was "no evidence of sustained community spread outside North America."

The potentially deadly virus is a hybrid drawn from strains found in pigs, birds and humans.

- AFP /ls