World health officials continue to see new human-to-human transmissions of swine flu in North America, but not on other continents, the World Health Organization said Thursday.

But the UN's top flu expert also warned the new strain of H1N1 flu virus still has the potential to infect up to two billion people in the next several months if it develops into a pandemic.

Dr. Keiji Fukuda, the World Health Organization's acting assistant director-general, said the figure wasn't a prediction, but that past experience with flu pandemics indicated it is "reasonable" to expect that up to a third or more of the world's population could get infected in the case of a pandemic.

The agency is not considering moving the pandemic alert up to Level 6, its highest level, Fukuda told reporters in a video teleconference from Geneva.

"We remain at Phase 5. That is not changed," Fukuda said.

"We continue to see human-to-human transmission, community-level transmission, primarily in North America," he said. "We are not seeing it yet anywhere else."

According to the UN health agency's Thursday tally, 2,371 people are infected with the virus in 24 countries, with 44 confirmed deaths from the illness in Mexico and the United States.

All but two of the deaths were in Mexico, where the outbreak of the H1N1 virus is believed to have originated.

Reports that emerged Thursday suggested an elderly Alberta woman who had swine flu has also died. Officials have not yet commented on the case.

Health officials will be tracking very closely whether the virus moves into the southern hemisphere, Fukuda said.

A Level 5 alert means there has been human-to-human spread of a virus in at least two countries in one region, according to the organization's pandemic response guidelines.

The classification means a pandemic is imminent and countries must finalize preparations to deal with the outbreak, officials said. Level 6 means a pandemic has occurred.

Pork safe to eat, says flu chief

Fukuda also said pork is safe to eat and that existing sanitary and animal health checks are sufficient to safeguard the food supply against the H1N1 virus.

"Eating pork is not a danger in terms of getting this infection," he said.

The U.S. Centers for Disease Control and Prevention said Thursday that the United States now has 896 swine flu cases in 41 states.

There are now 214 cases of swine flu in Canada. Another 13 new cases were confirmed on Thursday: seven in Ontario, three in Alberta, two in Saskatchewan and one in Quebec, all of them mild. Ontario now has the most cases, followed closely by British Columbia and Nova Scotia.

A staff member at Toronto's Princess Margaret Hospital was confirmed to have come down with a mild case of swine flu late Wednesday. The hospital did not release any details of the job the worker performs, but said she did not have direct contact with patients.