No, Seriously, How Contagious Is Ebola?

[morningfog]

"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.

Why is Frieden so sure this virus won't spread beyond a handful of cases?

It boils down to something called "R0."

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.

http://www.npr.org/blogs/health/2014/10/02/352983774/no-seriously-how-contagious-is-ebola

[lonestarnot]

1. I can't tell you how contagious is, but I can tell you how serious it is.

Series.....911, 19999911 snort.

[BlindTiresias]

2. Eh...

Not an accurate use or description of R0:

"When calculated from mathematical models, particularly ordinary differential equations, what is often claimed to be R0 is, in fact, simply a threshold, not the average number of secondary infections. There are many methods used to derive such a threshold from a mathematical model, but few of them always give the true value of R0. This is particularly problematic if there are intermediate vectors between hosts, such as malaria.

What these thresholds will do is determine whether a disease will die out (if R0 < 1) or whether it may become epidemic (if R0 > 1), but they generally can not compare different diseases. Therefore, the values from the table above should be used with caution, especially if the values were calculated from mathematical models.

Methods include the survival function, rearranging the largest eigenvalue of the Jacobian matrix, the next-generation method,[7] calculations from the intrinsic growth rate,[8] existence of the endemic equilibrium, the number of susceptibles at the endemic equilibrium, the average age of infection [9] and the final size equation. Few of these methods agree with one another, even when starting with the same system of differential equations. Even fewer actually calculate the average number of secondary infections. Since R0 is rarely observed in the field and is usually calculated via a mathematical model, this severely limits its usefulness.[10]"

[morningfog]

3. I know you want it to be more contagious, but

Not sure why.

[BlindTiresias]

4. I don't

But you are outright lying to people and misrepresenting data, facts, and methods of analysis.

For Ebola to be inconsequential its R0 needs to be lower than 1. That it is in the 1.5-2.0 territory is not comforting, as it can still become an epidemic and grow geometrically.

[morningfog]

6. Yes the article said all of that. You suggested the

article was incorrect.

[Old Crow]

12. Sheesh. Over the top much?

I see nothing whatsoever in the OP to justify your statement that the poster is "outright lying to people and misrepresenting data, facts, and methods of analysis."

That's not just over the top, it's way over the top, IMO.

DU is generally considered to be a friendly place where like-minded people trade ideas. Not a place for launching attacks at the drop of a hat.

[BlindTiresias]

13. Context

This person explicitly denied that Ebola was transmitted in all bodily fluids, even objects that still have bodily fluids on them or handshakes. The CDC disagrees. This person's comments would be considered a "lie" or "misrepresentation" if one is feeling charitable.

This person's characterizations of an R0 of 1.5-2.0 not being a big deal is also not accurate. Any r0 larger than one means that absent efforts to contain the epidemic it will continue until the vulnerable population has been burned through.

So yes, they are outright misrepresenting the facts of the matter by going too far in the opposite direction of hysteria. You want to be right in the middle.

[Old Crow]

16. Understood.

But you'd do better to object to the specific posts you have an issue with and not carry your grudges into other posts.

Regarding this post, the NPR article the poster cited doesn't trivialize the risks of Ebola. It's simply putting them into context. The article's main message is that in terms of transmission, Ebola is significantly less contagious than measles. I don't have a problem with that statement. Nor do I think the CDC would have a problem with it. And, frankly, I don't think you do, either.

[morningfog]

17. Oh bullshit. Link to it or shut up.

You are not accurately stating anything.

[Feral Child]

39. Drama.

Some folks need their daily fix, + hourly boosters.


Then again, some people are waiting impatiently for the Apocalypse.

I don't know your critic's posting history, but some "push" on this topic is purely emotional.

[uppityperson]

5. Here is an interesting article "can you catch ebola from an infected blanket?"

http://www.washingtonpost.com/news/to-your-health/wp/2014/10/03/can-you-catch-ebola-from-an-infected-blanket/

(clip)
The Ebola virus is highly infectious but not very transmissible. That may sound to a lay person’s ear like a contradiction. What this means is that very little virus – in animal experiments, as few as 10 virus particles (virions) – can potentially lead to a fatal infection. That’s the “infectious” part of the equation.

But it’s not easy for that virus to be transmitted. Ebola is much less contagious than measles or influenza. It’s not an airborne virus. It’s transmitted through bodily fluids. The overwhelming majority of people who have been infected with Ebola are people who have directly cared for a person who is actively sick with the disease or have handled the body of someone who has died from it.

(clip)

In one laboratory experiment, scientists couldn’t recover Ebola virus that had contaminated a surface kept at room temperature. In another study, Ebola virus kept at cold temperature was recovered from plastic and glass surfaces after more than three weeks. But Peter Jahrling, director of the Integrated Research Facility of the National Institute of Allergy and Infectious Diseases in Frederick, Md., doubts that in the real world the virus would survive nearly that long.

(clip)

Anyone dealing with the virus should be extremely careful, she said – because the consequences of a mistake are potentially so dire. “Because the outcome is so potentially dangerous – the case fatality is extremely high with this virus – you have to be extremely cautious. You need to take that extra step, because if you do have an exposure and if you are exposed to even a small quantity of the virus, the potential for a negative outcome is extremely high,” said Hensley.

[morningfog]

7. Good info.

[uppityperson]

8. Thank you. I found it in another thread.

[Fred Sanders]

41. THIS is the ANSWER. ^^^^^^^^^^^^^^^^^^^^^^ No more media hysteria, shall we?

[longship]

9. And that is determined by a variety of factors.

1. It only takes very few viral particles to infect a person, presuming that they get within your body. That's why washing hands and not touching your face are so important.

2. But other than that, it is not easily transmitted. It is not airborne, and is not likely to become so (no matter what the screaming meemies are screeching). So we have that going for is.

One might say, but, but, but, it's spreading like wildfire in West Africa and people there are saying that it could infect many thousands within a few weeks. What if it comes here?

There was no doubt that it would come here. The question is, what happens when it does?

3. The reasons why it is spreading in West Africa are the reasons why it will not spread here.

3a. West Africa has horrible medical and government infrastructures, amongst the worst on the planet. They are uniquely ill equipped to handle this, both medically and administratively.

3b. West Africa has cultural heritage -- E.G., burial practices, distrust of government and western medicine -- which help promote the spread of the virus. For Christ sakes, they mobbed and attacked an Ebola Ward to free the patients! Not good for containing the infection.

Just for DUer's info.

Relax people.

[morningfog]

11. And really all the unhinged people need to do is look at

Nigeria and Senegal. Case studies if containment. Compare to Liberia where hospitals are being ransacked and patients "freed."

[kestrel91316]

32. I fully expect to see the same idiocy from the denialists/antivaxer/antiscience/

anti-gubmint crowd right here if it comes to that.

People are plain stupid. And Americans are among the stupidest.

[gvstn]

10. I have a question

Was the guy at the news conference, I believe a judge, that said he had a wife and 9 year old daughter being responsible in his contact with the quarantined family? The family all spent time with the guy who was exhibiting symptoms for about 3-4 days. He went into the apartment but did not touch linens and other possibly contaminated items. He spent 45 minutes in a car with the family members who have not exhibited any symptoms. He wears the same shirt for two days and brags about it like it is some sort of badge of honor. He goes back to his own family and hangs out.

I realize he is trying to paint a picture of how difficult it is to catch Ebola virus but in the same breath considering his actions how can Texas be considering possible charges against the "carrier"? The "carrier" didn't do anything worse then the guy from the news conference.

[Zorra]

14. Don't worry, Ebola is not contagious,.

Keep shopping.

[BlindTiresias]

15. Furthermore

This is based on old data. Look up the corrected projections from the CDC and watch the R0 go into 2.0-4.0 territory, in the same neighborhood as smallpox.

[840high]

19. Thank you.

[uppityperson]

21. Link? Thank you.

[BlindTiresias]

23. Alright

http://www.cdc.gov/mmwr/preview/mmwrhtml/su6303a1.htm?s_cid=su6303a1_w



Essentially the health authorities in West Africa were under-reporting the number of infected by at least 40%.

[Old Crow]

25. You are misstating the information on the CDC website.

Yes, the charts show two sets of trend lines, one "Uncorrected," the other "Corrected."

But your statement that "Essentially the health authorities in West Africa were under-reporting the number of infected by at least 40%" is entirely wrong.

The authors of the paper are drawing on a modeling tool (EbolaResponse). The two trend lines seen in these charts are built into that model because it is understood among epidemiologists that diseases in countries with substandard healthcare facilities are likely going to be underreported as a matter of course.

There was no discovered event of underreporting by health authorities--no shocking error which the CDC is now scrambling to account for, as your erroneous--and somewhat alarmist--interpretation implies.

[BlindTiresias]

27. I don't mean to imply it was intentional or otherwise some shocking secret

They are overwhelmed and unable to properly account for the true number of infected individuals, which is what the adjustments are accounting for.

It still stands that the true number of infected people is likely more than what the previous numbers are saying.

Do you contest at all the adjusted number of infected by any chance? Not trying to level a gotcha at you, I am seriously wondering if you maybe have some competing data/models that contradict this.

[Old Crow]

29. How about an "Oh, you're right--I missed that"?

Acknowledging, and not glossing over, your mistake would go a long way in helping me dialogue with you in a serious way.

Yes, of course, the health authorities in West Africa are overwhelmed. How could they not be? The creators of EbolaResponse included that given within the charts produced by the tool, which is only sensible.

In terms of your statement that "the true number of infected people is likely more than what the previous numbers are saying," I have no indication that the figures the CDC has been using have been inaccurate. So I'm not sure what you're basing that on.

[BlindTiresias]

30. I mean

The adjusted number versus the unadjusted. Do you think the adjustments made were inaccurate at all?

Honestly I'm not glossing over anything, I only said there was under reporting of the number of infected by quite a bit according to the adjusted estimates. Maybe they are wrong and the numbers have been more or less accurate? Would like to read some competing information if you have any.

[Old Crow]

34. Are you asking if I believe the Corrected trend lines are inaccurate?

If so, no, I trust the epidemiologists who authored the model. They based their estimates of underreporting on the history of previous epidemics and math. I'm certainly not in a position to second-guess them.

You haven't asked, but to cut to the chase, here's my take on the situation.

1. The Ebola outbreak in West Africa is deadly serious and is going to result in shocking numbers of dead in the coming months. We haven't seen nothing yet in terms of the number of fatalities.

2. That said, provided the biology of the virus doesn't change, it is extremely unlikely that more than a dozen people within the U.S. will die of the disease. We have the CDC, thank God, and the resources to handle a highly deadly, but not very contagious, disease. Africa, alas, does not.

3. The frightening asterisk to this whole situation, which isn't discussed that often, is the possibility--remote, but possible--that the virus will mutate. Ebola is not very contagious now. If it mutates in just the right fashion, all bets are off. However remote the possibilities of a mutation are, every transmission of the disease from one individual to another provides the virus with more opportunity to make that lucky genetic leap that will allow it to find new hosts by a cough or sneeze. Since this is the largest outbreak of Ebola on record, the disease is being afforded more opportunities to mutate than ever before. Essentially, what is now going on in Africa is the creation---and illness, and often death--of thousands of human petri dishes. Soon, those human petri dishes will number in the tens of thousands and possibly hundreds of thousands. It is absolutely in the best interest of the United States that we do everything we can to extinguish this Ebola flare-up as quickly as possible.

4. Having said all of the above, Americans who are not working face-to-face with Ebola patients would make far better use of their time by scheduling a flu shot in the weeks ahead than by watching Fox News and worrying about a disease that poses far, far less a threat to them than a lightning strike, a car accident, or a bad case of the flu.

Hope that helps.

[Fred Sanders]

42. The curve for Uganda, Nigeria and Senegal has flatlined to 0.Ebola controlled. Why do you want to be

afraid?

[Old Crow]

43. Are you addressing me? Or someone else?

If you're addressing someone else, I'd suggest a self-delete followed by a repost in the correct location.

[Fred Sanders]

44. Meant for blindtireass. Sorry.

[uppityperson]

28. That is a very interesting link, thank you. I do not see R0 numbers there though

I will have to look more tomorrow when am on computer and not dumb tablet.

Thank you for the very interesting link. I like their explanation of burial practices, explains how people getncontaminated.

[BlindTiresias]

35. I'll try and find better data

My general point was that the numbers are being adjusted according to models being utilized by the CDC, however they are indeed using a conservative R0 in these models from what I can see. As the picture becomes clearer I think it is possible, maybe even likely, that the R0 for Ebola changes as we get a better understanding of how it behaves in established populations that are not isolated, rural villages.

I think we will also see whether the adjusted trendlines are conservative or not as well, or at least have a better idea.

Also as others have pointed out a R0 in the 2 area will still mess you up if efforts are not made to contain the spread of the disease, so I don't think the R0 alone should be too comforting for people, honestly.

[alphafemale]

18. We do not commonly walk barefoot across sharp stones in a common latrine area

And people often die of simple diarrhea in Africa and other places without clean water and sanitation.

I'm really not that concerned.

[BlindTiresias]

20. sigh

Can people please stop this? It doesn't need to literally enter an open wound from a contaminated puddle of feces in order to infect you. A simple handshake from a sweaty and feverish infected person could do it.

[uppityperson]

22. Have you gotten your flu vaccine yet?

[BlindTiresias]

24. This week, actually

And my son was last week. What is your point?

[uppityperson]

26. That is good, so did I.

[Warpy]

33. No case from sweat has yet been documented.

It's only theoretically possible.

[morningfog]

36. Not likely.

And that is not what happens in reality.

[kestrel91316]

31. R0 is not the only factor. There is no way to quantify

victims and contacts who lie, escape isolation, or withhold pertinent information. Nor is there a way to quantify computer systems that withhold vital travel history and other stupidity.

A low R0 is totally dependent on humans doing the right thing all the time.

[WinkyDink]

37. MY question: EXACTLY HOW did those cured US victims contract it? We've never been told.

[morningfog]

40. They were working in the trenches, so to speak.

One careless error, one faulty it lacking protective piece could do it.

I guess the question is do they know how they were infected. Can they say when it was, or is it just occur at some unidentified point?

[WinkyDink]

46. "I guess the question is do they know how they were infected." And that is what scares: Do THEY

even know how?

[Feral Child]

38. The real question

is, "How contagious are Ebola posts?



Kidding (mostly). You post has very good information. Thanks.

[magical thyme]

45. "on average" does not take into consideration individual circumstances

That is the problem with trying to apply statistics that are intended to determine what is needed to stop the spread of disease to how it works in real life.

In real life, how contagious is it depends on the viral load at the time of exposure, the amount of exposure, the type of exposure and the condition of the exposed person's immune system.

At an individual level, how contagious ebola is varies case by case and person by person.

Dr. Brantly didn't expose anybody else because he immediately self-quarantined. Same with Writebol, Sacra and other medical workers.

However, Duncan exposed everybody he was living with to one degree or another, along with numerous people in the ER on two occasions, plus the 3 EMTs that picked him up by ambulance.

Same with the pregnant woman who died, followed by numerous family members who took care of her dying, and now Duncan critical.