MIAMI — Patients with the H1N1 swine flu virus who become severely ill and those who die tend to be relatively young adults without underlying medical conditions, according to a new study.
The average age of 168 patients studied in 38 Canadian adult and pediatric intensive care units was 32.3 years. Thirty-three died within 90 days of being admitted to the hospital.
The study, released Monday in the Journal of the American Medical Association, suggests that H1N1 flu might be more complex than experts had believed.
Many had said the virus was most dangerous to people with underlying medical conditions such as asthma, diabetes, chronic obstructive pulmonary disease and immune system diseases. And experts say regular seasonal flu is most dangerous to the elderly.
"Our data suggest that severe disease and mortality in the current outbreak is concentrated in relatively healthy adolescents and adults between the ages of 10 and 60 years," the authors write.
But they say that modern therapies, including breathing assistance from ventilators and antiviral medicines, can prevent most swine flu deaths.
South Florida doctors agreed that the Canadian study suggests that H1N1 flu is not entirely understood.
"Most of the patients we've seen had underlying conditions or pregnancy," said Steven Katz, director of emergency services at Memorial Hospital West in Pembroke Pines, Fla. "But this is a new strain of flu. It's still early. Sometimes the facts change as diseases unfold.
"People die from the flu each year," he added. "This one is no worse than other flus, at least so far."
Most people with flu-like symptoms don't need to go to emergency rooms or even take antivirals such as Tamiflu, Katz said. Only people with severe shortness of breath or very rapid heartbeat should go to hospitals, he said.
The Canadian study, conducted between April and August, was authored by Anand Kumar of the Health Sciences Centre and St. Boniface Hospital in Winnipeg.
The fact that few of the severely ill patients in the study had underlying health conditions may be because the H1N1 virus primarily infects younger people, who tend to be healthier, the authors said. Older people — especially those over 65, who are more likely to have underlying conditions — appear to have some immunity because of long-previous exposure to similar viruses or to inoculations.
The study supported a statement Friday by the U.S. Centers for Disease Control and Prevention that swine flu is dangerous to children.
The CDC said 76 children younger than 18 have died of swine flu so far this year, while regular seasonal flu typically kills between 46 and 88 children a year. In the Canadian study, 50 of the 168 seriously ill patients were under 18.
Patients who became critically ill suffered severely low levels of oxygen in the blood, fluid in the lungs and, in the most serious, multisystem organ failure, the study said.