HOUSTON, July 9 (Xinhua) -- Texas health authorities on Thursday reported four more deaths and 473 new confirmed and probable cases of A/H1N1 flu for the past week, bringing the death toll to 21 and the number of total cases to 4,464 in the southwest U.S. state.

    The state health and human services department also said that, among the 21 deaths, 15 reported and confirmed in June, comparing to five in May and one in April, a Mexican kid died in a Houston hospital in late April as the first death of the A/H1N1 flu virus in the United States.

    Bordering with Mexico, Texas and California were the two U.S. states which reported first seven confirmed cases of A/H1N1 flu virus -- two in Texas and five in California -- on April 23.

    Since then, the new type flu has been circulating in both states, where reports of more deaths and widespread cases have been a common phenomenon in every week and every month.

    In Texas, the state health and human services department reported 28 confirmed cases on May 1, compared with 1,403 cases on June 1 and 3,991 cases on July 2, a remarkable jump for each month.

    As of Thursday, confirmed cases of the A/H1N1 flu virus reported in 120 of the state's 254 counties, with eight counties reporting their first confirmed cases for past week.

    Hidalgo County, near the border with Mexico, has been the hardest-hit with four deaths as well as 1,121 confirmed cases.

    Both state and federal health officials and experts believe those cases -- which sought treatment and underwent testing -- are just the tip of the iceberg. They estimate more than one million Americans have been infected with the virus so far, though many probably had only a mild illness.

   Special Report:  World Tackles A/H1N1 Flu