People, wearing face masks as a precaution against swine flu, walk after crossing from U.S. to Mexico at the San Ysidro crossing port in Tijuana, Mexico, 30 Apr 2009The World Health Organization says there is some concern the swine flu A-H1N1 virus may start moving from the Northern Hemisphere to the Southern Hemisphere, where the regular winter flu season is approaching.

WHO's Assistant Director-General Dr. Keiji Fukuda said most swine flue cases are still in North America , but there have been some incidents of the virus going south, and some travel-related infections in Europe and Asia. The virus has spread to Colombia - the first confirmed case in South America.

Dr. Fukuda says health authorities are monitoring the situation closely.

"We have concerns about the infection traveling to the Southern hemisphere, because that part of the world will be heading into the winter months, and the winter months are when influenza viruses usually thrive, and so you typically see epidemics and outbreaks of influenza occur during those colder months," he said.

Meanwhile, Mexico's Health Secretary Jose Cordova says most economic activity in his country will resume Wednesday, and said the outbreak there is waning.

Keiji Fukuda (file photo)
WHO's Assistant Director-General Fukuda stressed it is critical for countries everywhere to remain alert and keep monitoring the situation. He hailed the fact this level of surveillance is unprecedented.

"At this point in history, this is the best surveillance we have ever had," he said.

During a Geneva-based news conference, Dr. Fukuda said there were just more than 1,000 confirmed cases worldwide in a total of 20 countries, with 26 deaths, but cautioned that the numbers are constantly changing.

He made clear that if the World Health Organization raises its alert level from phase five to phase six, it will not be a statement about the severity of the virus, but would mean there is clear evidence of community level transmission in another region of the world outside North America. 

Fukuda also said there have been no further outbreaks of influenza in pigs. He said it had been reported there had been signs of the H1N1 virus in a herd of pigs in Alberta, Canada, but indicated he did not have any firm details. He again stressed that pork products do not pose any risks to people.

"The pigs are not the danger to people right now. It is really, the danger is the people transmitting the infection to other people," he said.

Despite this information, up to 20 countries worldwide have banned imports of pork and other meat.

U.N. Secretary-General Ban Ki-Moon also issued a strong warning that over-reactions to the virus should be avoided, including unnecessary travel restrictions and the banning of certain foods. He pointed out the livelihoods and well-being of millions of people across the world are at stake.