Global health officials say there are early signs that H1N1 swine flu activity may be peaking in the Northern Hemisphere, but that transmission remains active and geographically widespread in places like the United States.
The World Health Organization issued its assessment Friday as U.S. health officials said four patients at Duke University Medical Center in North Carolina have a form of the virus resistant to Tamiflu, an anti-viral drug used in treatment.
A statement obtained by the Reuters news agency quoted hospital officials as saying the four patients were very ill with underlying severely compromised immune systems and other health conditions.
Separately, World health officials said they are investigating samples of mutated H1N1 virus found in two Norwegians who died from the disease. Norwegian health officials said the mutation appeared to infect deeper in the respiratory system, causing a more serious illness.
The WHO says at least 500 people have died of the virus since last week, bringing the worldwide total to more than 6,770.
Data posted a week ago showed that 6,250 people had died from the virus since it was first discovered earlier this year in Mexico. The number of fatalities remains the highest in the Americas, where 4,806 deaths have been recorded so far.
The Asia-Pacific region posted 1,323 deaths, while at least 350 people died of swine flu in Europe.
Some information for this report provided by AP and Reuters.