H1N1 Swine Flu Deadly in All Age Groups
When Swine Flu Is Bad, It's Really Bad, Data Confirm
Nov. 3, 2009 - H1N1 swine flu isn't always severe, but when it's bad, it's
really bad. Patients hospitalized with pandemic flu have an 11% fatality rate,
data from California suggest.
The pandemic flu bug is far more likely to strike younger people. But when
people aged 50 and older get hospitalized with H1N1 swine flu, their
case-fatality rate is the highest of any group: 18% to 20%.
The findings come from an analysis of data collected from California
hospitals during the first 16 weeks of the U.S. H1N1 swine flu pandemic (April
23 to Aug. 11) by Janice K. Louie, MD, MPH, of the California Department of
Health and colleagues.
"In contrast with the common perception that pandemic 2009 influenza A
(H1N1) causes only mild disease, hospitalization and death occurred at all
ages, and up to 30% of hospitalized cases were severely ill," Louie and
colleagues report in the current issue of the Journal of the American
In a news conference, CDC Director Thomas Frieden, MD, MPH, said the
California data show that H1N1 swine flu is just as deadly as seasonal flu.
"What we have seen in that article and in our own data from around the
country and around the world is the level of severity among those who become
ill is similar to seasonal flu," Frieden said. "Although a much, much lower
proportion of people over 65 get H1N1 compared with seasonal flu, if they get
it, it can be every bit as severe."
Louie and colleagues note that the low median age of patients with severe or
fatal H1N1 swine flu -- 27 years -- makes the pandemic flu "markedly different"
from seasonal flu.
"A striking percentage of hospitalized cases were severely ill, with more
than 30% requiring intensive care; most adults and more than one-third of
children required mechanical ventilation," they write. "Eleven percent died;
the most common reported causes of death were viral pneumonia and acute
respiratory distress syndrome."
And as previous data have shown, pregnant women are at much higher risk of
severe flu than are other healthy women.
"Of note, 20% of hospitalized pregnant women in our series required
intensive care; most were in their second or third trimester of pregnancy,"
Louie and colleagues report. They note that similar observations were made in
the flu pandemics of 1918-1919 and 1957-1958.
Obesity a Risk for Severe H1N1 Swine Flu
As others have seen, more than 70% of adults and more than 60% of
children with severe H1N1 swine flu had underlying medical conditions.
The California data add to a growing body of evidence that extreme obesity
-- a body mass index or BMI of 40 or more -- is a risk factor for severe swine
flu. Nearly half of all the severe cases in California were in obese people;
43% had a BMI of 40 or more.
Louie and colleagues note that nearly a third of obese Californians with
severe swine flu did not have an established risk factor, although many had
other conditions such as high blood pressure.
"A link between obesity and severe influenza, while not proven, is
plausible," they suggest.
The CDC's Frieden agrees that obesity may well turn out to be an independent
"We are in the midst of an epidemic of obesity. It has doubled in adults and
tripled in children in the past couple of decades," Frieden said. "We are still
trying to understand what all of the implications of that are for people's
health. Increased susceptibility to infection is one, reduced respiratory
reserve and ability to fight off infections is another, but this is something
we need to learn that more about."