WASHINGTON, April 28, 2009 (AFP) - Despite relatively isolated outbreaks of swine flu, which has killed more than 150 people in Mexico, US experts insist the world is on the brink of a new pandemic.

The virus is "definitely verging on being a pandemic," said April Johnson, assistant professor of epidemiology and public health at Purdue University.

Johnson said thanks to air travel the flu -- now dotted in a few dozen towns and cities around the world -- had the potential to "become more established in different countries."

Richard Besser, acting head of the US Centers for Disease Control and Prevention (CDC), said he was "very concerned" by the spread of the virus.

"We are dealing with a new strain of influenza that appears to be moving through our community," he said, citing one of the characteristics in the level four of the World Health Organization's (WHO) six-phase pandemic alert stages.

The WHO late Monday raised its alert level to four, the last pre-pandemic phase on the scale.
Hours later, the CDC hiked confirmed infections in five US states to 64 from 44, and officials in the state of Indiana separately reported a case there.

If the virus spreads broadly in the United States, the WHO has said it could heighten its pandemic flu alert to level five, which is characterized by human-to-human spread of the virus into at least two countries in a single region.

So far, the CDC has confirmed only one case of human-to-human transmission in the United States beyond people who had recently traveled to neighboring Mexico, where the outbreak has its epicenter.

But Costa Rica on Tuesday became the first Central American nation to report a confirmed case, and Canada, Europe, Israel and New Zealand increased their counts of infected people.

Veratect, a company that uses artificial intelligence and human analysis to track and analyze emerging threats around the world, has seen "a huge uptick in respiratory disease in most countries of the world," chief executive Bob Hart told AFP.

"It's overwhelming, far above our normal tracking volume," he said.

"What we're seeing is a serious event, and it is spreading very widely, very fast," said Hart, whose company reportedly detected signs of the current outbreak in Mexico 18 days before the WHO posted its first public report on the disease on Friday.

But the world is better prepared now than it was just a few years ago to handle a pandemic, thanks to a trial run with the outbreaks of SARS (Severe Acute Respiratory Syndrome) and bird flu, said Dr Myles Druckman of SOS International, a medical services company which helps companies to put together plans for a pandemic.

"Everyone thought SARS and avian flu in 2004 and 2005 would be the next big thing. They pushed a lot of government agencies and businesses to develop their plans for a pandemic, and we're way ahead of where we would have been had we not been tested earlier," he said.

Homeland Security Secretary Janet Napolitano said the United States had enough anti-viral medication to meet demand, in the event of a pandemic.

"We have 50 million courses -- not doses, but courses" and states and the military also have tens of millions of courses between them, she said.

Purdue University's Johnson also tried to calm frayed nerves.

"A pandemic implies that this virus is widespread, but doesn't necessarily mean we'll see the number of deaths we have seen in historical pandemics," she said, pointing out that only one person died in the United States in the 1976 swine flu pandemic.