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There are still great challenges and great dangers — more on that later — but the big news is the abatement of the epidemic in Liberia.

Miracle in Liberia

Here is WHO’s chart of new cases in the country as a whole, and in the Montserrado district (which includes the capital, Monrovia). [WHO Current Ebola Situation Report]

Liberia_New_Cases_20141203

The drop, starting in mid-September, is breathtaking, even when figures from the patient database are adjusted by more realistic situation reports. There is now a big oversupply of isolation beds in Monrovia, and in some other parts of the country. The ready availability of beds certainly contributed to the drop in new cases, but other factors must also be at work since the fall began while all available beds were still occupied. I speculated on the reasons for the apparent drop in my previous post: Too Good to be True? I don’t have much to add, except that behavior must have dramatically changed in Liberia. Changing people’s behavior is very hard, especially when it relates to deeply-rooted cultural norms such as caring for loved ones and religiously-mandated burial practices. The message from Liberia is that behavior change is possible, and it can stop Ebola (in its current form) in its tracks.

The magnitude of the change is dramatic. The Reproduction Rate (defined in The Ebola Chain Reaction) for Liberia had been estimated in September at 1.51 [NEJM 9/23/14] , which is consistent with the left half of the charts shown above — exponential growth. The right half of these curves implies a Reproduction Rate far below the steady state of 1.0, which means that the rate dropped by at least a factor of two in a period of just a few weeks. It’s marvelous that such a large change was possible in such a short time frame. This affords a solid basis to hope that the same can be accomplished in the other affected countries.

The epidemic is by no means over in Liberia! We must not let down our guard, or infection rates could jump up again. But we can certainly take heart. It might also be reasonable to mothball the construction of new isolation facilities in Monrovia, keeping open the option of finishing them if they are ever needed. To the extent possible, new facilities should be constructed in Sierra Leone and Guinea, or perhaps under-served parts of Liberia,  rather than in Monrovia.

Steady Rate in Guinea

The rate of new cases jumped dramatically around the end of August and has continued at more or less the same level. This is a continuing severe epidemic, with Reproduction Rate around 1, but it is growing slowly if at all.

Guinea_New_Cases_20141203

WHO’s helpful situation report breaks the results down by region and points out a particular vulnerability in the northern area adjacent to Mali, which may lead to further spread to that country.  [WHO Current Ebola Situation Report] This is still a desperate crisis, but the slow rate of growth gives us time to get ahead of the situation. And the example of Liberia shows that control is possible.

Exponential Growth in Sierra Leone

The big worry now is Sierra Leone, where the rate of new cases is continuing to grow exponentially.
Sierra_Leone_New_Cases_20141203

Growth in Sierra Leone is country-wide, but the capital of Freetown presents the most acute problem because it is running out of beds. Once again, the WHO situation report describes what’s happening and the management plan: [WHO Current Ebola Situation Report]  We just have to hope that the miracle in Liberia can be replicated in Sierra Leone.

Concluding Observations

Just a few weeks back Liberia was the greatest worry, and the focus was on building isolation facilities there, especially in Monrovia. Now many of those facilities stand empty. Like a wily prize fighter Ebola ducked the roundhouse punch we had planned for it there, and is continuing to fight in other parts of the ring. This doesn’t mean that our plans were mistaken, or even unnecessary, since nobody could have foreseen the dramatic drop in transmission in Liberia. But it does mean that we need to be nimble in responding to where the greatest need currently is — Sierra Leone and the northern districts of Guinea. The need to redeploy resources is problematic, since it takes time and effort to design, build and staff a new facility. We have no choice, however: we must follow the epidemic wherever it goes.

So long as there is active transmission we are still exposed to two big risk factors:

  • spread to another country with crowded slums, traditional practices and a weak healthcare system, and
  • mutation to become more contagious.

I’m optimistic at this point that we can control the epidemic before either of these disasters occurs, but the need to end Ebola is still urgent.

 

 

 

 

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For months treatment centers in Monrovia have been turning away patients, who are then cared for at home, which places household members at high risk of infection. New treatment facilities have been filled as soon as they become available. Projections showed the need for ever increasing numbers of beds, for at least the next several months.

But suddenly, around the middle of October, reported cases and burials in Monrovia have started to drop. Some Ebola clinics are less than half full! [NYT 10/31/14]  [Economist 11/1/14] Can it be that the epidemic is waning? Or are appearances deceiving? On the same day Yale researchers warn that deaths could skyrocket, consistent with the earlier models of exponential growth. [Yale Daily News 10/31/14]

I don’t have a crystal ball, but I will just throw out a few ideas:

  • Home treatment kits started being distributed around the middle of October. [Reuters 10/20/14] This is a desperate stopgap, since patients become so highly contagious in the last stage of illness that caregivers and others in a household are likely to be infected. But is it possible that many people are using home treatment kits instead of taking patients to clinics? If so, the epidemic could be roaring ahead unnoticed. Except for this: where are the burials? To make sense of this hypothesis you would have to also assume that families were secretly burying their dead members (thus creating more opportunities for infection). While this has been reported it seems implausible that it would occur widely enough to impact statistics, especially in an urban context.
  • More hopefully, the worst Reproduction Rate seen for Ebola in this epidemic was 2.2, which, though ample to fuel exponential growth, is not that much above the steady-state level of 1.0. (See my earlier post for details). Also, transmission of Ebola is a function of human behavior: primarily incautious care-giving and the handling of dead bodies. It’s difficult to change people’s behavior but the crisis in Liberia may just have been sufficiently acute for this to happen. Many individual decisions just may have added up to success: not to touch someone who seems ill; to use a barrier when touch is necessary; to sterilize objects with chlorine bleach; to allow a body to be taken away without traditional cleaning and funeral rites.
  • This report is from Monrovia, the capital of Liberia. We must not lose sight of what’s happening in other parts of Liberia, and in the other countries with active transmission: Guinea, Sierra Leone, and now quite possibly Mali.

Meanwhile, a new 200-bed treatment unit opened on October 31 in Monrovia. This is a big addition to the 500 beds previously available. “The daily management of the treatment centre will be taken care of by the Liberian Ministry of Health and Social Welfare, with support from African Union and Cuban foreign medical teams.” [WHO 10/31/14] I hope it is never needed, and that unused Ebola facilities may perhaps become the nucleus of an improved ongoing healthcare system in these desperately poor countries.

Ebola Resources

Reproduction Rate

The way Ebola spreads is simple: from one person to another. There’s an African animal reservoir — probably fruit bats — from which the virus finds its way into a human being once or twice a year. But from then on the virus is transmitted only through bodily fluids, not via an animal vector such as mosquitoes or fleas. Ebola spreads by a simple chain reaction: each person it infects may infect one or more additional people, and so on. The key is how many susceptible people, on average, each infected person passes the virus on to. This is called the “Effective Reproduction Rate,” or “Re”. (Almost everyone* is initially susceptible to Ebola, but Re will drop proportionately if a substantial portion of the relevant population becomes immune, either by surviving or by receiving some future vaccine. The rate at which the virus would be transmitted in a completely susceptible population, with no immunity, is called the “Basic Reproduction Rate,” or “Ro”.)

  • If, on average, each infected person passes the virus on to just one other susceptible person (Re is one) the epidemic will continue at a steady rate, neither growing nor dying out. This is called an “endemic” disease. The total number of cases grows, but the rate at which new cases occur stays the same.
  • If Re is less than one the epidemic will die out, slowly or rapidly depending on where the number falls between one and zero.
  • If Re is more than one the epidemic will mushroom until some factor pushes that number back down below one. The rate of growth will depend on how big this number is, but the epidemic will relentlessly accelerate so long as Re is greater than one. This is “exponential” or “explosive” growth.

The only way to stop an epidemic is to push Re down below one. Of course it’s also best to get as close to zero as possible as rapidly as possible, but so long as Re is less than one the disease will eventually die out.

Forty Years of Rural Outbreaks

Ebola outbreaks have so far always started in rural areas, with the likely suspect usually being some sort of bush meat, typically bats or monkeys.

Home caregivers are very likely to be infected, so at the outset an Re of at least one is almost assured. Other family members and visitors are also at risk. This mode of transmission can be greatly reduced by caring for patients, as soon as they become infectious, in a facility that follows rigorous infection-control procedures. This approach has worked for Médecins Sans Frontières (“MSF”) in all prior outbreaks. (Lugubriously, this form of transmission may also be reduced when patients aren’t cared for by anyone, either because they are the last member of a family or because they are put out of the house when they fall ill.)

Healthcare providers are especially vulnerable, particularly in the early stage of the outbreak. The initial symptoms of Ebola are similar to those of many other less-infectious diseases, so the first wave of sufferers typically walk in to clinics or hospitals and are examined and cared for like other patients. Not only are doctors and nurses likely to become infected, but before the outbreak is recognized they may pass infection on to other patients. This is tragic, and definitely helped the current outbreak get a foothold, but it may ultimately not be an important element of Re. For one thing, MSF has shown that rigorous procedures and high-quality anti-infection suits can essentially eliminate this risk. As of a recent report, no MSF employees had become infected in the West African outbreak, though many other healthcare providers have been. For another, hospitals and clinics may be closed when they have become contaminated, and patients may stop going there for any illnesses once the risk of Ebola infection becomes known. The collapse of the health care system has many adverse effects, but the silver lining is the fact that people who don’t go to a hospital at all can’t either transmit or acquire Ebola there.

African funeral practices have played a big role in amplifying Re.

  • The body of someone who dies is traditionally hand-washed by members of the family. This almost guarantees that the washers will be infected.
  • Mourners at a traditional funeral may touch and even kiss the body. This can infect many people, who bring the virus with them when they return home. The entire outbreak in Sierra Leone, for example, has been traced to fourteen women who attended a single traditional healer’s funeral in Guinea. [NYT]
  • Finally, those who bury the body are at high risk unless infection-control procedures are used.

It is obviously essential to stop these funeral practices, since one victim can infect a huge number of other people this way. Again, MSF has been able to do this in the villages affected by previous Ebola outbreaks by working with local chiefs and explaining the situation to the villagers.

The impact of funeral practices on Re is affected by the mortality rate. In prior outbreaks up to 90% of those infected died, so almost all had the potential to infect many others through their funerals. In West Africa only about half seem to be dying, so the impact of funerals is somewhat reduced. This effect is swamped, however, by the large number of potential infections from one traditional funeral. Even though the reduced mortality rate makes funerals somewhat less important it is still essential to bring traditional funeral practices to a stop if Re is to be reduced below one.

In more than a dozen rural outbreaks over nearly forty years Re has been decisively driven below one, and the outbreak stopped, by rigorous infection control, contact-tracing and quarantine. The support of local communities was obtained by personal contact and education.

New Complications in West Africa

The West African outbreak, however, presents a very different picture. The health care systems in the affected countries had been damaged by years of civil war as well as profound poverty. This is the first time Ebola has appeared in any of these countries, so they were slow to recognize it and unfamiliar with the steps needed to contain it. Whatever the reasons, the virus was able to spread for several months before being recognized, and the consequences have been tragic.

Several new elements have complicated the relatively simple pattern of previous outbreaks:

  1. Ignorance, superstition and rumor have frustrated efforts to apply the established protocol, both in certain rural villages and in poor urban neighborhoods, notably the West Point district of Monrovia. Health care personnel have had to withdraw completely from a dozen “red villages” in Guinea where residents fear that MSF and Red Cross are causing Ebola rather than seeking to control it.[NYT] People have been hiding Ebola victims instead of letting them go into isolation wards.
  2. The uncontrolled spread of Ebola into several big cities raises the risk of additional modes of transmission, such as physical contact in taxis, buses and crowds, and contamination of shared surfaces.
  3. The number of patients has overwhelmed available isolation facilities.
  4. In several cases people who had been exposed to Ebola, or were already ill, have nevertheless chosen to travel, thus putting many others at risk. [Ebola Strategy 2014-08-31]  Some people have also lied about potential exposure to gain admission to hospitals, thus risking infection to doctors, nurses, staff and other patients.

The consequence has been that Re appears to be at least one in Guinea and Sierra Leone, and more like 1.5 in Liberia. An excellent article in Science projects a tripling to around 10,000 cases by September 24, and hundreds of thousands in subsequent months, with no end in sight so long as Re stays so high. [Science 2014-08-31].

The only way to stop the outbreak is to identify and implement a suite of feasible measures that together push and hold the Effective Reproduction Rate (Re) below one. It is of course also important as a humanitarian concern to provide the best possible care for those who fall ill, but care has no effect on the rate at which the virus spreads except to the extent that it implies reduction of potentially infective contacts.

The outbreak has naturally segmented itself to some degree, into rural and urban areas, and by country. A couple of attempts at quarantine barriers, called cordons sanitaire, have attempted to segment it further, with mixed success. (I plan to discuss this in a future post.) To the extent that segmentation works it may be possible to stop the outbreak using different suites of infection-reduction measures in different segments. In particular, relatively well-organized countries such as Nigeria and Senegal may well be able to bring their own smaller outbreaks under control using the standard protocol of contact tracing, monitoring and quarantine, even if the epidemic continues to grow uncontrollably in, say, Liberia.

Wild Cards

The current situation is bad enough without worrying about how it could get worse, but there are a few uncertainties that it’s useful to keep in mind.

Ebola is mutating rapidly,[Washington Post 2014-08-28] and it’s possible that the virus could change in ways that increase its infectiousness, especially through the air. That would be very problematic, to put it mildly.

An animal transmission vector might emerge, particularly in places where bodies are not promptly disposed of.

Sexual transmission might become significant in a promiscuous segment of the population, such as a subset of gay men. Not only could an infected person pass the virus on to multiple sexual partners, but this could also happen after recovery, since Ebola is found in the semen of recovered patients for up to seven weeks. [Who Fact Sheet]

Secondary effects of the outbreak could disrupt infection-reduction measures or even destabilize affected regions. The most immediate risk is a breakdown in food supplies, but one could also imagine breakdowns in other public services. Public disorder has broken out in several places, and this could continue or worsen. In the middle term the weak economies of the affected countries will be further damaged by disruption of internal and foreign trade. Also, the breakdown of the health care systems in these countries may facilitate epidemics of other diseases.

At the bottom of Pandora’s Box there is hope:

A safe and effective vaccine could bring the outbreaks to a fairly quick end. Indeed, this may be the only real hope of doing so.

Possible Preexisting Immunity A subsequent New York Times article raises the possibility that some portion of East Africans are already immune to Ebola. [NYT 9/5/14] The article cites a 2010 study in Gabon, which had had four Ebola outbreaks from 1994 to 2002. The study found Ebola antibodies in 15% of the population, ranging from 34% in some remote villages to 3% on the coast. The investigator speculated that many of the antibodies resulted from low-level exposures that weren’t sufficient to cause illness. This is interesting because it might afford a large pool of people who are already immune, who might be able to take on hazardous jobs with less personal risk, and who might be able to donate curative antibodies. There are several cautions, however:

  1. Immunity is to a particular strain.
  2. It’s not clear what level of antibodies is protective in humans.
  3. While an injection of antibodies might help an infected person fight off the disease it would not function like a vaccine to generate long-term immunity.
  4. Levels of exposure in Gabon, which had a long history of Ebola outbreaks, might be higher than in the countries currently affected.
  5. The epidemic is currently most worrisome in coastal cities, where antibodies would probably be lowest.
  6. Whatever preexisting immunity existed in remote villages wasn’t sufficient to keep Ebola from getting a foothold there.
  7. Sophisticated techniques are needed to test for antibodies.

More Information:
[Measuring Disease Dynamics in Populations: Characterizing the Likelihood of Control, Johns Hopkins]

[Exponential Growth and the Legend of Paal Paysam]