The number of children who have died from swine flu has jumped sharply as the virus continues to spread widely around the United States, striking youngsters, teenagers, young adults and pregnant women unusually often, federal officials said. The deaths of another 19 children and teenagers from the new H1N1 virus were reported in the past week around the country, including two in the state of Maryland, pushing to 76 the number of fatalities this year among those under 18, officials said. It was the largest number of pediatric deaths reported in a single week since the pandemic began in the spring. "These pediatric deaths seem to be increasing substantially," said Anne Schuchat, who heads the federal Centers for Disease Control and Prevention's National Center for Immunization and Respiratory Diseases. While most of the children who have died have had other health problems that made them particularly vulnerable, such as asthma, muscular dystrophy and cerebral palsy, 20 to 30 percent were otherwise healthy, Schuchat said. Between 46 and 88 children died from the seasonal flu in each of the past four years, so the fact that so many have already succumbed is disturbing, Schuchat said. "It's only the beginning of October," she said, noting that the flu season usually starts much later and runs through May. "We saw a peak of deaths, you know, starting April, May, June. It started to level off this summer. Now it's starting to shoot up again."