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When And Why Does H1N1 Become Deadly?

On the verge of a pandemic level label, the H1N1 virus has sickened thousands and killed nearly 100 people in 40 countries, according to the World Health Organization.

But why do some people get sick and others die?

Early Show medical correspondent Dr. Jennifer Ashton appeared on the show to talk about reasons why the virus can kill in some cases.

Some people, Ashton said, are more susceptible to the flu: the elderly, young children and people with chronic medical conditions or suppressed immune systems.

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But when people do get sick, Ashton said, they tend to go through a common pathway where their lungs become overwhelmed with both infection and inflammation. The condition is called "acute respiratory distress syndrome," which Ashton said may be a contributing factor to the number of H1N1 deaths.

"That really stacks the deck against them," she said.

Ashton showed the progression of this inflammation on chest X-rays from the Acute Respiratory Distress Syndrome Foundation.

Black areas on the X-ray, Ashton explained, are good. They represent oxygen flowing into the lungs, but on day one of the flu, the lungs may become partially blocked by fluid. This fluid is white on the X-ray, representing fluid or pus that blocks air passage.

And as time passes, Ashton showed the lungs becoming even more filled and whiter on the X-ray. By the third day, Ashton said, some patients like the one featured in the ARDS X-ray, would be on a ventilator to help them breathe.

"This is what we see in a lot of patients who succumb to influenza, pneumonia and die," Ashton said.

"If you have difficulty breathing and you're getting worse and not better, trust your body," Ashton said, "if you're feeling like it's the worst you've ever felt, see your doctor."

There are 8,829 confirmed cases of the H1N1 virus in 40 countries and 80 known deaths, according to the World Health Organization.

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