MEXICO CITY, July 2 (Xinhua) -- The A/H1N1 flu has killed 337 people in 121 nations and regions and the number of the total infected exceeded 80,000, a top official of the World Health Organization (WHO) said on Thursday.

    Most of the infected are young people, and schools and homes are the places where people are most likely to be infected, WHO Deputy Director -General Keiji Fukuda told a meeting on the A/H1N1 flu in Mexico's southeastern resort town of Cancun.

    He said the virus is more similar to H5N1 avian flu rather than the seasonal flu and the future of the disease is uncertain, but the existing anti-viral medication remains the most effective treatment.

    The A/H1N1 flu death toll in the United States has reached 170, while the confirmed and probable cases risen to 33,902, according to the latest statistics of the U.S. Centers for Disease Control and Prevention (CDC) on Thursday.

    The CDC said that 43 more deaths have been reported in the past week, a 34 percent jump from the previous record of 127.

    The new virus, H1N1, has a protein on its surface that is less efficient at binding with receptors in people's respiratory tracts than bird flu and seasonal flu, according to a report in Friday's edition of the journal Science by researchers at the Harvard University-Massachusetts Institute of Technology Division of Health Sciences and Technology.

    The researchers also noted that H1N1 is more likely to cause intestinal distress and vomiting than seasonal flu, and should be closely watched in case it mutates to become easier to spread.

    In Canada, the national total of confirmed cases stood at 7981, and the death toll rose Thursday to 31, with a newly reported death of a 60-year old woman from Quebec province. The Health Department is reminding people with severe symptoms such as trouble breathing and sore throats should go to see doctor.

    The El Salvador Health Ministry announced Thursday the first death from the A/H1N1 flu of a nine-year-old boy in the country.

    The National Health Institute of Colombia reported Thursday eight more cases of the A/H1N1 flu, which brings the number of confirmed cases to 101 in the country, including two deaths. Currently, 1,491 possible cases have been registered in Colombia.

    Uruguay's health authorities confirmed in a statement two more deaths of the A/H1N1 flu, bringing the total fatalities to three in the country, and the number of confirmed cases has reached 132.

    The Brazilian Health Ministry announced on Thursday 44 new confirmed cases of the flu, putting the total at 737 in the country, where 1,049 suspected cases of the flu have been reported.

    British Health Secretary Andy Burn warned Thursday that H1N1's infection rate in Britain could reach 100,000 a day by the end of August following the trend that a "considerable rise" of the flu cases took place last week and the cases are doubling every week.

    The British Health Protection Agency announced Thursday that a further 518 patients in England had been confirmed with A/H1N1, while the figure for Britain as a whole rose to 7,447.

Special Report:  World Tackles A/H1N1 Flu