A study of people who became seriously ill and died with the new pandemic swine flu confirms it is hitting a younger population than the seasonal flu and causes often different symptoms.

The study of 272 patients sick enough to be hospitalized showed about 40 percent had diarrhea and vomiting - usually rare with seasonal flu - and confirmed that quick treatment with antivirals could save lives.

Dr. Seema Jain of the U.S. Centers for Disease Control and Prevention, who led the study, said the findings had informed the CDC’s advice on who should worry about the new H1N1 virus and when to get treatment.

“Of the 272 patients we studied, 25 percent were admitted to an intensive care unit and 7 percent died,” Jain’s team wrote in the report, published in the New England Journal of Medicine.

They said 45 percent were children under 18, just 5 percent were over 65 and 73 percent had at least one underlying condition such as asthma, diabetes, heart disease and pregnancy.

The soonest any of the patients who died were treated with an antiviral drug was three days after they started showing symptoms, the researchers found. Patients treated earlier all survived.

Roche AG’s Tamiflu or GlaxoSmithKline’s Relenza should be given within 48 hours of symptoms to be the most effective. But Jain said it was never too late to try.

“We really believe that antivirals should be started as soon as possible in patients who are hospitalized,” Jain said in a telephone interview.

Even if patients do not have the traditional risk factors for serious disease, they should get antiviral drugs if they are sick enough to be hospitalized, Jain said.

FEVER AND COUGH

The cases her team examined represented about a quarter of the hospitalized H1N1 patients in the United States between May 1 and June 9 of this year, before the epidemic was declared a pandemic by the World Health Organization.

All the patients had fever and cough, 42 percent of the children had diarrhea or vomiting, and all of the patients 65 and older had an underlying condition. Some studies suggest people born before 1952 have some immunity to the H1N1 virus.

Of those whose height and weight were available, 29 percent were obese and 26 percent were morbidly obese. Jain said the percentage of people who were obese reflected the general U.S. population, but only 5 percent of the population is morbidly obese.

Some other studies have suggested that morbid obesity - defined as having a body mass index or BMI of 40 or higher - may raise a person’s risk of serious complications and death from H1N1. Jain said that question needed more study.

The study found that 7 percent of the hospitalized patients died, and all of those who died had been on ventilators. Those who died ranged in age from 1 year to 57 years.

Those who died were more likely to have been short of breath, to have pneumonia, a neurological disorder or acute respiratory distress syndrome. They were also less likely to have received a seasonal flu vaccine over the past year.

In its weekly report on death and disease, another CDC team found that 41 percent of children aged 6 months to 2 years got a seasonal flu vaccine last year, 32 percent of 2- to 4-year-olds, 20 percent of other children aged up to 17, 32 percent of young adults, 42 percent of 50- to 64-year-olds and 67 percent of those over 65 - who have the highest risk of severe illness or death from seasonal flu.

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By Maggie Fox

WASHINGTON (Reuters)