Why Are Virus Outbreaks Often Not As Bad As First Feared? : Shots - Health News Why do outbreaks caused by flu and other viruses often seem worse initially than they turn out to be?
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Why Are Virus Outbreaks Often Not As Bad As First Feared?

Why do outbreaks caused by flu and other viruses often seem worse initially than they turn out to be?

That's the question Jon Hamilton examines in a report on All Things Considered this afternoon.

As Hamilton explains, it all has to do with how many people are in the denominator and how sick they are. The relatively fewer there are and the sicker they are, the worse the situation looks. Hamilton talked with Dr. Rob Fowler, a critical care physician in Toronto, to understand what doctors there saw when SARS struck in 2003.

HAMILTON: At first, it appeared that SARS was killing nearly 50 percent of the people who got infected. But as the outbreak progressed it became clear the true death rate was closer to 5 percent.

Fowler says it took awhile before doctors started looking for SARS in people who weren't critically ill. And that made the disease look even more frightening than it turned out to be.

As in the SARS case, once doctors expanded the denominator in the swine flu situation, including the many more patients with very mild illness, the apparent severity of the disease diminished.