No, Seriously, How Contagious Is Ebola?

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.

"I have no doubt that we will control this importation, or case, of Ebola so that it does not spread widely in this country," said the director of the CDC, Dr. Tom Frieden.

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. (When everyone is vaccinated, the R0 drops to essentially zero for measles).

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.

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.

But in Ebola's case, the mode of transmission probably helps keep its R0 low. Ebola isn't spread through the air, like the measles or flu. It requires close contact with some bodily fluid, such as blood or vomit, containing the virus.

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.

*We're talking the "basic" R0 here, for all you epidemiologists. So, the R0 that you get when everyone in the population is susceptible to the disease.

**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.

People with Ebola infect fewer people than the mumps...because people are scared to death of getting Ebola.

Yes, and that's due to the other half of this calculation that was omitted from this reassurance: none of these diseases carries with it a 70% mortality rate (with the exception of measles in an unexposed population, which is very high but still not 70%). In short, you're less likely to contract the disease on exposure but more likely to die of it if you do. That's the issue here.

I think Obama has plans to engage the Ebola virus, and anticipate that he will soon announce plans to negotiate with Ebola. But, first, we all must acknowledge the virtues of Ebola. Ebola is a virus of peace, a virus dedicated to fairness, and equality, and humanity. No genuine Ebola virus would wantonly kill journalists and innocent children. What we are witnessing is the perversion of a great virus. We will offer to support moderate strains of the Ebola virus to isolate and eliminate this perverted strain of Ebola.

Hope’n’Change is Obama’s strategy to hand this perversion of Ebola.

In Africa the number of infections doubles every 21 days.

Let's see where we are 18 days from now in Dallas. And then 21 days after that.

But I BELIEVE I was the first on this forum to bring up the fact that this disease is easily transmissible between multiple species. I contend there are dozens of sewer rats...and potentially landfill rats/coyotes now contaminated in the Dallas area.

This disease is very likely now endemic to Dallas County. We'll see it pop up every few years just like West Africa.

Further problems not so far noted include:

Nothing effective is being done to prevent more index cases from arriving at random locations.

As soon as the 1st US health care worker turn up +, a critical mass of them are going to stay home, and we’ll rapidly devolve to 3rd world care levels.

Patient 0 went to a hospital after exhibiting symptoms. Did they quarantine him immediately? No. They sent him home with antibiotics...(wrong to do in any viral infection like the flu but done by incompetents anyway). He threw up outside, and it lay on the ground for days, before being cleaned up. Cleaned up by people not taking any precautions (incompetents). The daughter of the house offered to give them bleach...(someone with a little sense). They have not decontaminated the living space of patient 0, and the linens and other items cannot be transported for proper disposal.

These are the people that want to be in control of that golden egg called healthcare. They are not organized or fearful enough to do the job right. I have great wonder about what precautions our poor servicemen and women are going to be availed when they arrive at those hot sites rife with potential infection opportunities.

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