MELVILLE, N.Y. — Fatal cases of swine flu result from a devastating form of lung damage virtually identical to the pulmonary devastation caused in the 1918 and 1957 global flu outbreaks, confirming that H1N1 is more like its pandemic cousins than seasonal strains of influenza, scientists reported Tuesday.

But while autopsy data of 34 people who died of H1N1 earlier this year adds yet another chapter to medicine's knowledge of pandemic influenza, another study suggests that by the time the current flu season is over, H1N1 will not have been a potent threat to most people.

The autopsy studies involved people who died between May 15 and July 9, and revealed a consistent pattern of deeply penetrating damage throughout the lungs' lower airways, said Dr. James Gill of the New York City medical examiner's office, which conducted the study along with the National Institute of Allergy and Infectious Diseases.

"Pathologically, it's very similar to (autopsy findings) in the 1957 and 1918 pandemics," Gill said, noting as previous studies have also revealed, a preponderance of flu deaths in younger people — infants to adults up to age 49. Seasonal influenza, by contrast, is most devastating among the elderly, he said, and primarily causes upper respiratory infections.

Dr. Jeffrey Taubenberger, a pioneering flu scientist at NIAID in Maryland, added that the autopsy cases also revealed evidence of secondary bacterial infections, mostly pneumococcal pneumonia and methicillin-resistant staphylococcus aureus — MRSA. These bacterial culprits took advantage of the lungs' weakened state and were able to penetrate into the tissue and exacerbate the victims' respiratory distress.

"Over 90 percent of the cases had an underlying medical issue, primarily cardiac disease, respiratory disease or immunodeficiency," Taubenberger said, adding that 72 percent of the 34 people were morbidly obese, a condition that may have also caused respiratory insufficiency.

Gill said death was swift for all who succumbed to swine flu, a course that proceeded rapidly downhill within a matter of days. Some people died before hospitalization, he said.

But despite the bad news, a U.S. and British team of scientists in mathematical studies of the swine flu pandemic say that by the time it's over it will have produced a fatality rate of only 0.1 percent, or one death for every 1,000 symptomatic cases.

Via McClatchy-Tribune News Service.