Thick clouds of smoke from wildfires in the United States have exposed millions of people to harmful levels of pollution. The smoke is causing emergency room visits to jump and may have led to the death of thousands of older and sick people. That information comes from a study of pollution records by The Associated Press, or AP news agency. The AP also spoke with doctors, health officials and researchers about conditions on the U.S. West Coast. For at least one day, smoke from the wildfires topped concentration levels that the government says increase health risks. In recent weeks, the smoke has covered areas where more than 8 million people live, the news agency said. The state of Oregon has been hit especially hard by the wildfires. Last month, Oregon’s major cities suffered the highest pollution they have ever recorded. Powerful winds worsened fires that had been burning in remote areas and sent them toward the city of Portland. Medical problems began while communities were still covered in smoke. It led to hundreds of additional hospital emergency room visits each day in Oregon, state health officials say.