Wednesday, October 15, 2014

Ebola thoughts

 HIV is a pretty well known and understood virus. We know that it is a blood bourne virus, and the only way to get it is to share body fluids with an infected person. That means that if you do not expose your blood to the bodily fluids of a person infected with the virus, you won't get HIV or AIDS. With that being said, about 50,000 people per year are diagnosed with HIV. About 60% of the people who are infected with HIV go on to develop AIDS. Of the ones who develop AIDS, about 25% of them die.So, to summarize, HIV has a mortality rate of about 15%.

Health care workers have been dealing with blood borne pathogens for decades, and have little trouble preventing its spread in health care settings.Of course HIV is pretty difficult to catch. Epidemiologists have calculated a reproduction number, or R0 (pronounced R-nought) to estimate the number of individuals who contract a disease from an infected and contagious individual. In the case of HIV, that Ris 4, meaning that each person with HIV transmits that disease to 4 others, on average.

Epidemiologists are estimating that the R0 for Ebola is 2, meaning that, on average, each person with Ebola will pass the disease on to 2 other people. Of course, they are also saying this about Ebola:
 Ebola, which is transmitted only by contact with infected bodily fluids, is not contagious until the patient begins to show symptoms. Once contagious, concern is warranted, because Ebola fatality rates approach 50 percent, especially without proper treatment.
 Of course, there are some obvious falsehoods here. It turns out that the mortality rate for Ebola is closer to 70% than it is to 50%. It also turns out that the disease may not be purely blood bourne, as previously thought. Think about this: You have a pair of nurses who caught the disease, presumably from being exposed to infectious materials that were expelled from the Index patient. These nurses, if they are like the workers that I know, are intimately familiar with blood bourne diseases like HIV and Hepatitis, being that they likely see multiple patients with one of those diseases several times a day.

Instead, we find out that the hospital has the staff that is treating Ebola patients wearing positive pressure respirators. When was the last time you heard of a medical team wearing respirators for HIV or Hepatitis patients? Compounding this, we have an NBC reporter who reportedly had no known contact with any Ebola patients, and reportedly caught the virus from riding in a taxi that an infected person had previously ridden in. He had been in Liberia for less than 24 hours when he began showing symptoms. (He arrived in Liberia on Tuesday, and was diagnosed on Wednesday) That particular fact opens all sorts of scary possibilities.

Perhaps the disease has changed, and a new strain is more infectious than previous ones. That would give us an R0 that is higher than 2. How much higer would need to be determined. Let's face it: Duncan has already infected his two patients.

Let's talk about treatment.

Sure, the mortality rate here in the US is pretty good: Of the 6 patients treated here in the US, one has died, three have recovered, and two are in the early stages of treatment. Of course that is when you have 6 patients in a nation of 300 million. When it takes 70 people to treat one patient at a cost of several million dollars, you have to ask yourself how many times we can make such an effort before we run out of resources. Two of the patients were saved because they received the blood of a survivor. How much blood can he give? What about people who do not match his blood type? What happens when supplies of disposable suits and respirators run out?

Let's do some math:

Assume that the Ris still 2. There are currently an estimated 15,000 people with the disease worldwide. With an R0 of two, and considering that people become contagious and die in less than a month, we are going to see the number of cases double every month. That means that a year from now, there will no longer be 15,000 people with the disease, there will be over 245 million people with active Ebola infections. Assuming that the 70% mortality rate holds steady, by this month next year, the worldwide death toll from the disease would be 344 million dead.

Raise the R0 to 4, and those numbers become MUCH worse. With an R0 of 4, everyone in the world would have the disease by July, and more than half of the world would be dead of Ebola. That is what makes this disease so different, because HIV has an R0 of 4, but that number is stretched out over the several years that it takes an infected person to succumb. In the case of Ebola, the disease runs its entire course in less than a month, so an Ebola patient will infect his two patients within a week or two, whereas the HIV patient takes years to infect 4.

Of course, deaths on that scale probably won't happen. The reason for that is that the R0 would fall rapidly at some point. Why? Because humans can be a fear driven, panicked herd, just like any animal that perceives its survival is at stake. Once a disease like this takes off, society will begin to break down as antisocial behaviors take over.

See a hundred or two hundred cases of Ebola happen in the US. Schools will close, either by government decree, or by unspoken agreement. People will stop going to work, will stop gathering in large groups. Medical personnel will stop going to work. People will stop interacting. At some point, rioting will ensue. This will continue until the disease burns out.

From a purely scientific stand point, this is interesting to watch. At the same time, I think that we are either deliberately being lied to, or the experts are being proven wrong. Either way, these are the same hospitals that cannot control or prevent the 1.7 million hospital acquired infections in the US each year, which kill 100,000 people each year. Because of that fact, I do not believe them when they say that they have this under control.

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