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October 16, 2014

Flashback: Let NPR Reassure You That Ebola Isn't a Big Worry

Isaac Asimov used to say, "I wish I were young enough to know everything."

His students would correct him: You mean you're not old enough to know everything.

Asimov would reply: I meant what I said. I wish I were young enough to know everything.

Let's turn the clock back to October 2nd, when NPR and the CDC were young enough -- inexperienced enough -- to think they knew all they need to know about ebola.

nprRnaught.jpg

Holy moly! There's a case of Ebola in the U.S.!

That first reaction was understandable. There's no question the disease is scary. The World Health Organization now estimates that the virus has killed about 70 percent of people infected in West Africa.

The Ebola case in Dallas is the first one diagnosed outside Africa, the Centers for Disease Control and Prevention said Tuesday. And the health care system in Texas didn't quarantine the man right away. He was sick with Ebola -- and contagious -- for four days before he was admitted to the hospital.

But when you look at health officials responding to the case in Dallas, they seem cool as cucumbers, despite the initial misstep.

...

The reproduction number, or "R nought," is a mathematical term that tells you how contagious an infectious disease is. Specifically, it's the number of people who catch the disease from one sick person, on average, in an outbreak.*


Take, for example, measles. The virus is one of the most contagious diseases known to man. It's R0 sits around 18. That means each person with the measles spreads it to 18 people, on average, when nobody is vaccinated...

At the other end of the spectrum are viruses like HIV and hepatitis C. Their R0s tend to fall somewhere between 2 and 4. They're still big problems, but they spread much more slowly than the measles.

And that brings us back to Ebola. Despite its nasty reputation, the virus's R0 really isn't that impressive. It typically sits around 1.5 to 2.0.

Even in the current epidemic in West Africa, where the virus has been out of control, each person who has gotten sick has spread Ebola to only about two others, on average.

Why is that?

With exponential growth, the numbers can get big, quickly.


Many factors contribute to the R0, such as how long you're infectious** and how many virus particles are needed to make another person sick.

...

Now at this point, you're probably thinking, "OK. But an R0 of 2 is nothing to brush off." You're right. R0 of 2 means one person infects two people, who then infect four people, then eight, 16, 32 -- the numbers go up fast.

But that isn't likely to happen in a place with a good public health system, like the U.S. Why? Because people with Ebola aren't contagious until they show symptoms.

So to stop the chain of transmission, all health workers in Texas have to do is get the people possibly infected by the sick man into isolation before these people show signs of Ebola.

Then R0 drops to zero. And Texas is free of Ebola.

"All you have to do."

Well we did that. And two nurses are now infected, and possibly they have passed ebola on to others.

What annoys me in the NPR article is a couple of things:

First, it is the habit of writers -- particularly progressive-leaning ones -- to assume the mantle of Expert Opinion when what they're really doing is regurgitating some things they understand very incompletely (if at all) from an hour's worth of internet research.

This is an extraordinarily annoying pose.

Second, it is the habit of progressive writers to regurgitate the claims made by bureaucratic "experts" uncritically. The NPR writer might have paused to wonder, for example, if getting everyone who may have been infected by Duncan into isolation was really as much of a snap as the "cool as cucumbers" CDC people made it sound.

Because, it turns out, it wasn't a snap at all.

Third, the pose struck here -- that any concern about ebola is probably pretty silly, given how great our health care system is, and how easy it will be to get Ducan's secondary infections into quarantine -- is just unearned.

The post affects a glib, blithe no-worries-mon posture about a major disease killing thousands. While Tom Frieden of the CDC was quite wrong in all of his glib, blithe claims, at least Tom Frieden is actually an epidemiologist. He is entitled to have such opinions about matters, based on his knowledge base and experience. (He was disastrously wrong, but at least he has the sheepskins to justify having an opinion on the matter.)

But so many of these progressive bloggers assume that same sort of tone -- I'm Talking About Science, Now You Kids Listen To Me -- based on... what exactly?

"Loving Science"?

That out of the way, let's dispel some confusion buzzing around ebola here, in terms of medical terminology. Ebloa is not an "airborne" pathogen, and yet it can be transmitted by a sneeze.

What does this mean?

Apparently what it means is this: Some diseases produce airborne particles that literally just hang around in the air. Rather like the "weaponized anthrax" particles, I suppose. Such "airborne" diseases can hang around like a little cloud of infection for up to an hour, if the air is undisturbed. You could, conceivably, walk into such a cloud of aerosol particles and become sick, even having never directly made contact with the transmitter of the illness, nor being in the same room as him at the same time.

That's an "airborne" disease. Ebola has never been observed infecting someone through that sort of no-contact-at-all transmission.

But yes, sneezes are still contagious. They're not considered "airborne" because they will not remain in the air any longer than gravity permits them to. When someone sneezes, he is transmitting his illness through the air, but that's not considered "airborne," because it's not really airborne. It's a projectile spray which will hit the ground in a second unless another human being is unfortunate enough to intercept it.

Someone infected with ebola can infect you by sneezing on you.

Incidentally, when they say ebola requires "direct contact" with emission? Per that article, a sneeze which touches your own wet membranes counts as "direct contact."

That's something that the CDC isn't really making clear to us, huh?

Sharyl Attkisson notes that some virologists are objecting to the CDC's insistence on telling the public that ebola is not an "airborne" illness, given the term's propensity to obscure what scientists mean, rather than illuminate.

A commentary published last month by the Center for Infectious Disease Research and Policy at the University of Minnesota highlights the points of contention.

In the article, national experts on respiratory protection and infectious disease transmission say the CDC may be wrong. They say CDC’s protocol of masks, gloves and gowns isn’t enough to protect health care workers treating Ebola patients: they should be equipped with respirators.

"It's imperative to favor more conservative measures," say the authors.

"We believe there is scientific and epidemiologic evidence that Ebola virus has the potential to be transmitted via infectious aerosol particles both near and at a distance from infected patients, which means that healthcare workers should be wearing respirators, not facemasks."

According to the article, "The precautionary principle--that any action designed to reduce risk should not await scientific certainty--compels the use of respiratory protection for a pathogen like Ebola virus that has: No proven pre- or post-exposure treatment modalities, A high case-fatality rate, Unclear modes of transmission."

In fact, the experts argue, the very term CDC is using, “airborne,” is outmoded.

They explain that modern research shows that aerosols emitted from the respiratory tract contain a wide distribution of particle sizes--including many that are small enough to be inhaled.

“We recommend using 'aerosol transmissible' rather than the outmoded terms 'droplet' or 'airborne' to describe pathogens that can transmit disease via infectious particles suspended in air," write the authors.

So far, the CDC is sticking with its terminology and position, insisting Ebola is not airborne.

Let's take a look at two other terms: "infectious" versus "contagious." The experts keep saying ebola is highly infectious -- but not very contagious.

"Contagious" is actually what most people are thinking about when they wonder about how dangerous a disease is. "Contagiousness" is how easy a carrier transmits a disease to another person.

As you can see from NPR's chart, ebola is not particularly contagious -- but it's still contagious.

"Infectiousness" refers to something probably only doctors and nurses care about. "Infectiousness," from what I can gather, refers to a somewhat technical idea of how little, or how much, of an infectious dose is required to infect a person.

Ebola is one one of the most infectious diseases in the world. You can catch ebola, theoretically, from only one particle of the disease -- 1-10 particles is enough for an infectious dose.

Common diseases usually require 1000 or more disease particles to infect someone.

I think this explains why health workers wear the hazmat suits, and yet experts tell people to not worry so much about contagiousness. A health worker must make sure he doesn't get a single particle of the stuff on him -- and he's going to be constantly exposed to such particles, treating a patient.

But in the case of casual contact, transmission requires an unlikely (though still possible) direct spray of saliva via a cough or sneeze (or the other body fluids). In fact, the article linked above says that that spray must make contact with your own "wet membranes," that is, the inside of your mouth or, maybe, who knows, your eyes.

All that said, something needs to be remembered here: We've known about ebola since 1976.

But we have never had an outbreak like this before.

Apparently -- and this is just what some of the more "alarmist" experts say -- ebola is very likely to mutate. One of the great fears of this latest outbreak is how long-lasting it is, and how many cycles of reproduction ebola has had/is having/will have.

Every time ebola reproduces, it may mutate. It apparently is "sloppy" when it duplicates itself. Its mutations may make the disease weaker; some mutations may make it completely ineffective at infecting anyone at all.

But some mutations may make it even more dangerous.

The fear is that in this latest bout of ebola, with tens of thousands of people infected, ebola is given enough rolls of the Mutation Dice to become even worse than it is.

And this may actually have happened. I don't know why ebola is worse now than it has ever been before, but it is. One possibility is that it has become, somehow, marginally easier to transmit than in previous outbreaks, so maybe rules from previous outbreaks -- and the insistence that "We know how to stop ebola" -- might be misplaced.

Oh, one more thing

Now NPR's article was written two weeks ago.

But meanwhile, another "expert" -- by which I mean "Leftwing blogger with no discernible expertise" -- still is very much Young Enough to Know Everything, this very day.

Adam Serwer reports that Rand Paul said that Ebola is more infectious than HIV. He then giggles himself silly as he posts a chart which he purports to show that Oh no you don't, HIV is more "infectious."

There are many things wrong with this chart. For one thing, he is conflating infectiousness with contagiousness.

Fine, whatever, the chart speaks of "infectiousness." People think "contagiousness," which is fine, because that's what the chart is showing.

But even beyond that, this Alleged Science Lover Adam Serwer just doesn't seem to love science very much. For if he had checked -- the NPR article notes this -- one can't compare the contagiousness rates of HIV vs. ebola without also noting this:

**The R0 is integrated over the time that a person is infectious to others. For HIV, this could be years. But for Ebola, that time is only about a week. So even though they have similar R0s, Ebola's infections per unit of time is much higher than HIV's.

Per the chart, ebola's R-naught is about 2.4, and "untreated HIV's" R-naught is about 3.4.

So yes, HIV does wind up infecting slightly more people on average than ebola. But it does so over a period of years. The average HIV carrier will infect 3.4 people, over the course of five years, eight years, twelve years, etc.

On the other hand, an ebola carrier will infect 2.4 people over the disease's life cycle of 2-4 weeks. After 2-4 weeks, the carrier is either dead or he's beaten ebola. Either way, he's no longer infectious.

But this is the way of those who "Love Science" so very much, isn't it?

Corrected: tsrblke said I was wrong to use "airborne" and "aerosol" as synonyms. He says they are opposites, with "airborne" meaning "hanging around in the air" and "aerosol" intended to mean particles carried in expelled water droplets, as by a cough or sneeze.

I assume he's right, but I don't know for sure. So I've simply removed all references to "aerosol" from the post.

I believe as rewritten it simply sidesteps this question of terminology entirely.


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posted by Ace at 05:50 PM

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