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Related to: Forty Days , Low Hanging Poop

From professor Gregory Cochran's blog West Hunters.

Laurie Garret has an article out in the Washington Post.  She say that there’s no point in trying to block the spread of Ebola by travel bans.

The problem is, she’s full of crap.  Look, there are two possible scenarios.  In both of them, r, the number of new cases generated by each case, is greater than 1 in parts of West Africa – which is why you get exponential growth, why you have an epidemic.  If r < 1.0, the series converges – a case generates a few extra cases before dying out.

Everything we know so far suggests that even though it is greater than 1.0,  r in West Africa is not all that big (maybe around 2), mostly because of unfortunate local burial customs and incompetent medical personnel.

It seems highly likely that r in US conditions is well under 1.0 which means you can’t get an epidemic. However,  r is probably not zero.  It doesn’t mean that you can’t get a few cases per imported case, from immediate contact and hospital mistakes.  As an example, suppose that on average each case imported to the US generated a total of two other cases before dying out (counting secondary, tertiary, etc infections).  Then, on average, the number of US citizens infected would be twice the number of infected visitors.

Now suppose that a travel ban blocked 80% of sick people trying to fly here from Liberia.  We’d have 80% fewer cases in US citizens: and that would be a good thing. Really it would.  Does Laurie Garret understand this?  Obviously not. She is a senior fellow for global health at the Council on Foreign Relations, but she is incompetent.  Totally useless, like virtually everyone else in public life.

We hear people from the CDC saying that any travel restrictions would backfire, but that’s nonsense too.  One might wonder why they say such goofy things: I would guess that a major reason is that they were taught in school that quarantines are useless (and worse yet, old-fashioned), just as many biologists were taught that parasites are really harmless – have to be, because evolution!

In the other scenario, r > 1.0 in US conditions as well, or at least is greater than 1.0 in some subsets of the US population.  This is very unlikely- even more unlikely considering we can adjust our behavior to make transmission less likely.  But suppose it so, for the sake of argument.  Then you would want – need – to stop all travelers from the risky regions, because even one infected guy would pose a huge risk.  Some say that blocking that spread would be impossible. They’re wrong: it is possible*, although it wouldn’t happen, because we’re too crazy.  In fact, in that scenario, we’d be justified in shooting down every plane that _might_ carry an infected passenger.  This scenario is the one that fits Garrett’s remarks, but if she really believed it, she would be frantically buying canned goods and finding a cave in the Rockies to hide her family in.

*the Atlantic is pretty wide.

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We hear people from the CDC saying that any travel restrictions would backfire, but that’s nonsense too. One might wonder why they say such goofy things: I would guess [...]

One might wonder it indeed. It would be nice if one had actually devoted research to the question rather than guessing poorly.

Honestly, without any attempt to understand the other side at all, this seems irrelevant to LW.

without any attempt to understand the other side at all, this seems irrelevant to LW.

I don't agree. If Cochran is right than either the CDC is lying because it feels we can't handle the true (i.e. it's better to let <10 Americans die of Ebola than to inflict lots of economic harm on West Africa), or fuzzy refuse-to-accept-tradeoffs-thinking infects CDC analysis. (I'm not competent to judge if Cochran is right.)

Barring the omission of the CDC being wrong for mundane reasons, the possibilities you listed (CDC right, CDC wrong and lying, CDC wrong and biased) are in fact all the possibilities. Reading this article does not appear to have actually restricted what you think could be true about the world, at least not enough to be worth mentioning!

I mean, yes, the possibilities you mention are interesting and LW-relevant. But this article actively avoids any actual information about why the CDC is against travel restrictions - possibly a consequence of the author's extreme confidence that they're right.

The five paragraphs up to that point are engaging with the explicit reasons that Laurie Garrett gave in the linked article. It's almost as if you made no attempt to understand the article and just mined for quotes.

I think the analysis that an r1 disease is correct, and that Cochran is right and Garrett is wrong when it comes to comparing ebola to the flu. As a factoid about someone being wrong in the media, it is of tepid interest to LW. If it were only this, I would simply say that this probably belongs in the open thread.

My desire to see it on this site becomes negative only because of the author's habit of insulting all people and major organizations that disagree with him rather than expressing even one google-search's worth of curiosity in what the CDC's argument is.

The CDC learned from earlier outbreaks that were mismanaged and where travelbans backfired.

http://www.amren.com/news/2014/10/cdc-chief-why-i-dont-support-a-travel-ban-to-combat-ebola-outbreak/

We don’t want to isolate parts of the world, or people who aren’t sick, because that’s going to drive patients with Ebola underground, making it infinitely more difficult to address the outbreak.

Prevention Director Tom Frieden said the CDC would consider any and all precautions, but warned that a travel ban could make it harder to get medical care and aid workers to regions dealing with the outbreak. - See more at: http://www.theyeshivaworld.com/news/headlines-breaking-stories/263717/cdc-director-travel-ban-could-make-ebola-outbreak-worse.html#sthash.xXK2239g.dpuf

Hm, seems you are right. I just skimmed these specific references for quotes. I do clearly remember to have read about travel-bans backfiring but can't right now locate suitable sources. This at least provides specific lessons learned:

QUARANTINE AND ISOLATION: LESSONS LEARNED FROM SARS http://biotech.law.lsu.edu/blaw/cdc/SARS_REPORT.pdf

1. Travel restrictions Lessons Learned Restrictions on travel are essential in limiting the geographic range of an epidemic, yet travel restrictions involve the difficult balancing of public health with human rights and economic interests. Further, the marginal public health benefit from ratcheting up restrictions may not be predictable. All of the countries we studied followed the WHO recommendation concerning exit and entrance screening for SARS, addressing ground and sea as well as air travel. Under the intense pressure of the SARS outbreak, many countries were forced to adopt novel approaches to population risk assessment and disease containment, including thermal screening to identify febrile persons at risk for SARS. The countries we studied placed restrictions of varying stringency on domestic travel. News of the global SARS epidemic caused the voluntary curtailment of international travel to affected areas. Travel advisories and travel alerts from WHO and individual countries helped to provide timely and accurate information.

Prevention Director Tom Frieden said the CDC would consider any and all precautions, but warned that a travel ban could make it harder to get medical care and aid workers to regions dealing with the outbreak.

Isn't that the point? (The Israeli government has apparently bowed to more pressure, though.)

This thread seems to be someone of questionable (nothing mentioned or demonstrated) expertise asserting without evidence that the experts don't know what they are doing. No attention is paid at all to the costs of the proposed action or why the experts think it won't work. Without any evidence the prior for this being crackpot territory is very high. Downvoted.

[-][anonymous]7y 1

I assumed familiarity with Gregory Cochran:

Gregory M. Cochran (born 1953) is a physicist and adjunct professor of anthropology at the University of Utah, known for hypotheses in evolutionary medicine and genetic anthropology.

A few cases in places where they can likely be contained are probably better than writing off millions of people to be burned through. It's not even just an ethics decision - (high rate of travel better contained focus) is better than (low rate of travel near-universal infection).

This, of course, is contingent upon it being able to be contained when single travellers transmit the virus. Given the containment of the cluster in Nigeria, I am optimistic about that.

It's not even just an ethics decision - (high rate of travel better contained focus) is better than (low rate of travel near-universal infection).

Huh? Why does low-rate of travel imply near-universal infection?

One doesn't follow from the other, they come from the same source. Cutting off most travel = less outside help and therefore more local infection, as well as lower rate of travel out. However, allowing the exponential to continue unabated means you soon get such a high level of infection that the lower level of travel is even worse.

Obviously you can limit travel in any way you want: you can let health workers go in and out while blocking regular travelers. Or, for that matter, you could block everyone under 20, everyone over 40, and everyone called Murphy. It does not have to be all or nothing.

If you were trying to make sense, you would let health workers fly in and quarantine them for three weeks on the way back: that's not much of an inconvenience, considering the risk. And you wouldn't let locals fly elsewhere for the duration.

" Liberia" was short hand: I mean the several countries in West Africa where the epidemic exists.

You know, discussions in this forum have a truly unusual flavor.

" Liberia" was short hand: I mean the several countries in West Africa where the epidemic exists.

That assumes that you have good data real time data about the epidemic.

If you start strongly punishing countries for revealing data about local epidemics you soon don't have that data anymore.

Obviously you can limit travel in any way you want: you can let health workers go in and out while blocking regular travelers.

As the article describes the one person who actually did spread the disease to the West was the nurse Teresa Romero Ramos. Health workers are much more likely to come into contact with bodily fluids and get the virus than the average person wealthy enough to buy plane tickets.

If you start strongly punishing countries for revealing data about local epidemics you soon don't have that data anymore.

The effect of "punishing" is not linear, it only matters if it reaches a threshold. So as long as any travel ban comes with more aid (which seems likely), the info will be revealed as before.

The effect of "punishing" is not linear, it only matters if it reaches a threshold.

No. Even a little amount of punishing can weaken relationships and reduces the amount of information that gets transferred. It can also produce time lags.

Fear of punishment is also not the only reason why a politician might want to prevent knowledge of a local epidemic in a remote village from spreading. There can also be inner political reasons.

If you look at the original article by the CDC person, they speak about lack of trust that might make it hard to distribute vaccines. While trust is a resource that doesn't really grow linearly it's not about threshold effects.

So as long as any travel ban comes with more aid (which seems likely), the info will be revealed as before.

Still each decision to reveal critical information would become a though political decision, where politicians would have to assess whether it would cause more harm than good. This could lead to delays and downplaying.

Also, no matter what politicians do, individuals also respond to incentives:
People who visited a blacklisted country might lie about it in order to travel, people from a blacklisted country could travel to a neighboring non-blacklisted country and then travel using forged documents. Once they travelled illegally, they may delay getting medical assistance when they get sick, lie about where they have been, lie about people they have been in contact with, etc.

It looks like an iterated prisoner's dilemma: if you start defecting, then other players will defect against you, yielding a worse outcome for everybody.

A Phd life scientist told me that the Ebola virus has an easier time surviving in cold than hot weather. If this is true and significant, we can’t necessarily assume that we will do much better than West Africa in controlling Ebola, although the scientists told me she thought there was little chance of Ebola killing a large number of Americans.

She is a senior fellow for global health at the Council on Foreign Relations, but she is incompetent. Totally useless, like virtually everyone else in public life.

Want to solve this problem? Become a public servant.

That works if the problem is a self-selection bias. If there are counterproductive selection biases whose source isn't the selectees, or even if there's just an insufficient net bias in the right direction (what tiny fraction of people wouldn't be nearly useless at solving global health problems?) it's going to be harder to solve.

Given the conspiracy theory post last month, this takes a bit more intellectual effort to dismiss.

Now suppose that a travel ban blocked 80% of sick people trying to fly here from Liberia. We’d have 80% fewer cases in US citizens: and that would be a good thing. Really it would.

This is just wrong. There no reason to assume that every possible case of Ebola in the US comes from somebody who fly to the US from Liberia. Other countries will be less likely to share information with the CDC so the risk coming from other countries and other epidemics rises.

There no reason to assume that every possible case of Ebola in the US comes from somebody who fly to the US from Liberia.

What, are you saying that Ebola will form in the US by abiogenesis? If indeed r<1.0 for Ebola in western countries then any outbreak in a Western country is likely to be contained. Thus the only outbreaks in US will come from someone who just came from East Africa.

Other countries will be less likely to share information with the CDC so the risk coming from other countries and other epidemics rises.

Huh? Why would this happen?

What, are you saying that Ebola will form in the US by abiogenesis?

I'm saying that Liberia is not the only country with Ebola.

Huh? Why would this happen?

If a country can expect a travel ban when it shares information about an epidemic in that country it might prefer to keep that epidemic from being public knowledge.

If a country can expect a travel ban when it shares information about an epidemic in that country it might prefer to keep that epidemic from being public knowledge.

Good luck covering up these kinds of epidemics.

You won't be able to cover up every epidemic. But you can cover up a handful cases.

Even if you fail to really cover up those case it might add a time lag of a week till the WHO and the CDC have information, which means that they can respond less efficiently to the thread.

If you want to get people to change their burial rituals it's also important that you have trust. If you use travel bans in a way that suggest that you don't care about the local health then you don't have that trust. You can't give people vaccines when they don't trust you.

Given the low risk we Westerns face from Ebola, the trust is simply worth more. It's highly valuable in case an pandemic comes along that actually does threaten us.

The Coase theorem would seem to come into play here. We should be able to pay West African nations enough to compensate them for any harm of a travel ban.

We could make that payment in kind, too, to avoid the possibility of money going straight into the rulers' pockets. That payment in kind could be in the form of health workers and equipment going there to help fight the outbreak.

Which...is happening.

[-][anonymous]7y 0

I'm not sure this would fully solve the problem Christian mentions in the second half of his comment. The problem is that trust is priceless, which may impose very high transaction costs.

Given the conspiracy theory post last month, this takes a bit more intellectual effort to dismiss.

That thread really illustrated LW's problem with understanding texts that are non-literal. I thought Cochran's "conspiracy" post was really funny--I especially enjoyed the allusion to Elvis being "The King" in Cochran's scenario.

Recent CDC estimates put the amount of possible Ebola cases at around 1.4 million as of January 2015. This is just four months from now; however, they do not say what will happen one year from now based on their own, projective, logic.

If the current rate of transmission persists, with an exponential doubling time around 1 month, the human population will be infected to 2016. This will happen. There will be a thousand more cases in just 10 months… It just grows exponentially from there: five million cases as of Sept 2015; 5 billion cases by Sept 2016, i.e. the total human population. At a 70 % mortality rate, only 2 billion people will survive, but the situation could be even worse if we take into account mutations of the virus and the consequences of a pandemic catastrophe... http://brighterbrains.org/articles/entry/does-the-ebola-virus-constitute-an-existential-risk

Projecting ebola cases though 6 orders of magnitude as if the exponential will definitely continue unmodified through all limits is so wrong it's not even funny. (I have the same objection to projections of Moore's law or economic growth.) SO many curves have pieces of them that look exponential... though it is true that the exponentials usually come from the early parts of such curves.

Viruses mutate but a membrane-bound filamentous virus that doesn't live in epithelia as its main host cells is never something that becomes stable airborne, and other evolving viruses change virulence or symptoms not mode of transmission. You don't just change fundamental physical attributes.

Still a scary disease that must be contained, most especially from entering other poor urban areas where it is capable of exponentiating and could be utterly horrifying. But cut the bad math and baseless fearmongering in favor of its actual issues.

EDIT: This is not to say pandemics are not a big deal. Pandemics are actually probably the worst actual risks humans will face this century, seeing as the world situation is kind of perfectly primed for zoonotic disease by population growth habitat destruction urbanism and mobility. This is the sort of thing we will have to deal with for a long time. We'd better get used to it and get good at it or we will regret it.

Viruses mutate but a membrane-bound filamentous virus that doesn't live in epithelia as its main host cells is never something that becomes stable airborne

Can you explain like to a non-cellbioguy, what does the above sentence mean in relation to this?

Yes! Thanks for pointing me at that paper, I hadn't seen it before.

Enveloped viruses are in general much more fragile than non-enveloped viruses. They contain the genetic material of the virus and viral proteins surrounded by a lipid membrane derived from the membrane of a host cell, which they then fuse with the membrane of another host cell to get the genome in. Easier entry to the host cell at the expense of fragility. If the membrane is broken the virus is dead, and a bubble of membrane is a lot more fragile than a protein/RNA crystal (which is basically the entire structure of non-enveloped viruses which need to somehow pass through the cell membrane without killing the cell which is more difficult). In particular, dessication tends to kill enveloped viruses fairly quickly meaning they need to be wet from host to host. Ebola viruses are filamentous viruses, meaning their genome is stretched out in a long ribonucleoprotein fiber which is surrounded by a big tube of membrane (those long funny shapes we have all been seeing), so they have a lot more membrane per particle than most viruses and are particularly vulnerable.

One might note that the flu virus is also membrane-bound but goes through the air. Sort of. It empirically requires droplets of several microns in size to move through the air in natural conditions, which only make it so far (a few feet) before drying out or settling to the ground. In real-world conditions smaller droplets or dry particles don't seem to be important for its spread, though you can set up experiments where a few manage to make it through that way. Also, any flu virus that gets breathed in or on a mucous membrane is already in its perfect environment - epithelial cells - so a very small viral dose is required to make it in, whereas in living organisms ebolaviruses seem to have a much lower affinity for epithelial cells than blood vessel or connective tissue cells from research I've been able to look up, so you need more viruses to get into and infect a surface.

In the above-linked experiment, monkeys had their heads put in a sealed 8-liter box inches away from a nebulizer that produced aerosols from a liquid containing ebolaviruses, kicking up single-micron-sized droplets. They found that in this circumstance as few as 400 functional virus particles delivered this way to the respiratory tract/face was enough to cause a lethal infection (as compared to <10 functional virions via injection, though they did not try lower viral levels for inhalation), showing that a smallish number of freshly-aerosolized viruses landing on a respiratory surface can cause disease.

However, that you can set up an experiment in which you give enough viruses through the air to cause infection does not mean that under normal conditions that circumstance is likely to happen - the latter being the usual definition of 'airborne'. There's also a difference between 'airborne' and 'screwed if someone sneezes on your face' which is more akin to what's happening here.

They note this. Quotes from the paper:

"Epidemiology studies of human disease outbreaks in sub-Saharan Africa did not suggest that aerosol transmission of filoviruses was likely in that setting [emphasis mine]. Virus did not spread easily from person to person during the Ebola virus epidemics in Africa, and attack rates were highest in individuals who were in direct physical contact with a primary case... no cases occurred in children whose only known exposure to the virus was sleeping in the huts occupied by their fatally ill parents."

"It is possible that the quantity and distribution of virus within most patients' respiratory tracts may have been below the level needed to establish effective aerosol transmission."

The structural factors that make Ebola more fragile in the air are not ones that are likely to change much via mutation - that's things like cell affinity, how obvious it is to the immune system, replication speed, or toxicity to infected cells. There's reasons that viruses generally don't change their modes of spread during evolution.

On the other hand, there's this:

"Both elevated temperature and relative humidity (RH) have been shown to reduce the aerosol stability of viruses... Our experiments were conducted at 24C and < 40% RH, conditions which are known to favour the aerosol stability of at least two other African haemorrhagic fever viruses... If the same holds true for filoviruses, aerosol transmission is a greater threat in modern hospital or laboratory settings than it is in the natural climatic ranges of viruses... As previously stated, aerosol spread was implicated in the spread of disease among the monkeys at Reston [an accidental 1990s outbreak of ebolavirus among monkeys in a laboratory of a strain that could not infect/cause disease in humans, after work I may look up more about it to see what they mean about 'implicated']"

And this:

"While both parenteral [injected] and aerosol exposure to Ebola virus cause a systemic disease involving all organs, monkeys exposed to viral aerosols during our study developed strong immunoreactivity for Ebola virus antigen in airway epithelium, in oral and nasal secretions, and in bronchial and tracheobronchial lymphoid tissue. By electron microscopy, viral replication after aerosol exposure occurred in the lungs and tracheobronchial lymph nodes, and extracellular virus accumulated in alveoli of the lung." The monkeys exposed via fresh aerosol developed much more shedding virus in the lungs than their needle-exposed counterparts which you could imagine affecting infectivity.

You may find another paper making the rounds about aerosol transmission between monkeys and pigs; these were in a cage separated by bars and space and scientists make note that in that circumstance they can't necessarily tell the difference between respiratory aerosols, splashed liquid, and liquid kicked up during periodic cage cleaning.

Thanks a thousand times. That was awesome!

If you're interested here's an article that refers to several more aerosol related Ebola papers.

Thank you for writing this clear and well-researched post, really useful stuff.

In cold air droplets could live much longer. This is why we have flu outbreaks in winter. Ebola was never "tested" in winter conditions but it could become more contagious in winter in Europe and Norther US. Anyway, the question will it become airborne or not is not important as it already has doubling period 1 month and it is enough to infect almost all human population to 2016. To be airborne is only an option. The main question is how and when exponential growth will be stopped? What is your opinion?

5 billion cases by Sept 2016

...and 40 billion cases by December 2016. Beware exponential extrapolation.

This joke maybe good in any other site but not on Lesswrong which is based on idea of unlimited AI self-improving. Of cause Ebola will end it exponential growth - I just interested to know how and when. Will it burn out in Africa, or we get herd immunity after 100 million victims, or effective vaccine will be created, or we will nuke all places with Ebola?

This joke maybe good in any other site but not on Lesswrong which is based on idea of unlimited AI self-improving.

Some people here, including the founder, believe that recursive AI self-improvement is a realistic possibility, but I'm pretty sure that even the most hardcore believers acknowledge that there are physical limits, and that you can't just expect an exponential function to be a good fit for a trend when you get close to the limit.

The basic function you should be looking for modelling this kind of phenomena is the logistic function. It's the basic model for phenomena that include both positive feedback mechanisms (e.g. self-replication) and negative feedback mechanisms (e.g. resource constraints).

If you look at the graph of the logistic function, you may notice that initially, when positive feedback is dominant, it very closely resembles an exponential, then it becomes about linear around the middle point and then, negative feedback is dominant, it becomes close to a negative exponential.

If a disease had a constant basic reproduction number $R\_0 > 1$, and it could infect anyone, and infected people never died because of the infection and remained infectious for life, then the prevalence of the disease over time would be well approximated by a logistic function, with the world population size as the supremum value (the "capacity").

In an actual epidemic, of course, people can die or heal, and the R factor varies over time as the disease spreads to different places, people and institution change their behavior, better treatment becomes available, and so on, thus you don't really get an exact logistic trend, but that's the first-order model for forecasting the long-term prevalence disease, not an exponential model that neglects feedback loops.
An exponential model is only useful when the disease prevalence is still quite far from the capacity, that is, when a typical infected person is mostly surrounded by uninfected (and infectable) people.

So, do you think that half of the population will be infected?

No.

[-][anonymous]7y 6

If the current rate of transmission persists, with an exponential doubling time around 1 month, the human population will be infected to 2016. This will happen.

http://xkcd.com/605/

http://xkcd.com/1007/

SCNR.