Doctors are reporting a severe form of swine flu that goes straight to the lungs, causing severe illness in otherwise healthy young people and requiring expensive hospital treatment, the World Health Organization (WHO) said Friday. Some countries are reporting that as many as 15 percent of patients infected with the new H1N1 pandemic virus need hospital care, further straining already overburdened healthcare systems, WHO said in an update on the pandemic. “During the winter season in the southern hemisphere, several countries have viewed the need for intensive care as the greatest burden on health services,” it said. “Preparedness measures need to anticipate this increased demand on intensive care units, which could be overwhelmed by a sudden surge in the number of severe cases.” WHO Director General Margaret Chan, meanwhile, told France's Le Monde daily that the prevailing AH1N1 virus was spreading four times faster than other viruses and 40 percent of the fatalities were young adults in good health, “This virus travels at an unbelievable, almost unheard of speed,” Chan said. “In six weeks it travels the same distance that other viruses take six months to cover.” “Sixty percent of the deaths cover those who have underlying health problems,” Chan said. “This means that 40 percent of the fatalities concern young adults – in good health – who die of a viral fever in five to seven days. “This is the most worrying fact,” she said, adding that “up to 30 percent of people in densely populated countries risked getting infected.” More than 2,180 people around the world have died from the virus since it was uncovered in April. Some tropical countries are already reporting strains on their healthcare systems amid surges in infections. H1N1 has reached epidemic levels in Japan. Chan also said that it could be months before sufficient vaccine is available to combat the pandemic. She put world production capacity at 900 million doses a year, for a global population of 6.8 billion people.