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Hold the Chicken Little

April 26, 2013

The news came out of China this week that a strain of bird flu known as H7N9 has broken into the human population. It’s infected 82 people, of whom 17 have died — a mortality rate of 21 percent — and is suspected of human-to-human transmission.

At that point you, like us, might be wondering about air travel and global pandemics and whether it is in fact time to panic, hoard canned goods and shotgun shells and sit up late at night, sweating, with your copy of John Barry’s The Great Influenza.

The answer is no, says Arthur Reingold,  a professor of epidemiology and associate dean for research at the UC Berkeley School of Public Health.  Yes, public health officials should always be very concerned about a new strain of influenza, but so far H7N9 doesn’t look like death astride a pale horse, coming for us all. (Our words, not his.)

“One can be fairly sanguine, not get too alarmed, not change one’s behavior, and not think that the sky is falling,” Reingold said.

The reports of human-to-human transmission?

“At the moment, reports are, shall we say, sketchy,” Reingold said.

For example, in addition to the small number of cases so far, the reported transmissions have been among family members, who could easily have encountered a sick bird at different times or even at the same time but then have sickened at different times. It’s hard to be sure. More worrisome is when doctors and nurses who have treated the sick become ill themselves — in those cases, it’s much more likely that human-to-human transmission has occurred.

Bird-to-human transmission is bad, but it’s not nearly as serious. Birds we can avoid. Birds we can slaughter. It’s when the virus passes between humans that those systems break down.

A virus must achieve three things to become a pandemic, Reingold says.

  1. It must be virulent. It must make us sick, very sick.
  2. Humans must not already have antibodies against it (most flu viruses pass this test)
  3. It must pass easily from human to human.

And — call this step three and a half — while becoming transmissible between people, it must not have lost its virulence. (You know what we call a virus that spreads everywhere and makes people mildly ill? The common cold.)

Oh, and by the way, regular old influenza kills lots of people in this country every year. In the years between 1976 and 2007, the Center for Disease Control estimates the annual death toll ranged from 3,000 to 49,000 people. In the week ending in April 15, the most recent data we have from the CDC’s city monitoring program, suggests that 7.2 percent of all deaths were from pneumonia and influenza (the two are difficult to disentangle).

So far H7N9 has not demonstrated that it can pass easily from person to person. Reingold says the odds that it will are slim, though no one is certain exactly what the odds are because flu viruses are constantly having sex with other viruses and evolving. But H5N1, the first avian flu we started worrying about, has been around for maybe 15 years and it hasn’t picked up the ability to pass between people.

So you can rest easy. Except … well, another global flu pandemic is inevitable, Reingold says.

“It’s sort of like a major earthquake in California,” he says. We know there’s one coming, but we don’t know if it’ll hit L.A. or Berkeley or when it’ll hit.

“We know that there’ll be future influenza pandemics. But it’s very hard to say how severe they’ll be or when they’ll be. And anybody who thinks they can make that prediction is basically a fool.”

Sleep tight.

—Brendan Buhler

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