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.

So IF: The virus is found in bodily fluids, that would include saliva and sputum, yes? Lets say a person is sick with Ebola and sneezes or coughs, aerosolizing that sputum and saliva into the air that an uninfected person breathes. You are saying,"No chance what so ever of catching it." I assume you would not mind testing that theory out personally, yes?

What if that person just recently vomited and sneezes or coughs? Or they are already bleeding from the gums due to existing periodontal conditions? Or they have nose bleeds? Bite their cheek or tongue?

That scenario is typically referred to as "droplet transmission" and has never been ruled in or out as a mode of transmission of Ebola. To avoid droplet transmission, you should stay at least 3 feet from an infected person (this applies to all diseases that cause sneezing and coughing and are spread by droplets). I prefer to stay further than that from someone who is sneezing--3 or 4 yards is good.

The symptoms of Ebola include vomiting and diarrhea, which are the virus's way of exiting the body and looking for a new host.

But in Ebola's case, the mode of transmission probably helps keep its R0 low.

MICHAELEEN DOUCLEFF is giving us old information - numbers from past Ebola outbreaks. Here's how this strain is different:

ALL past Ebola outbreaks started in the jungle and moved toward cities. This outbreak started in a city.

All other Ebola outbreaks started in ONE place - a small village or community.... This outbreak STARTED in THREE cities simultaneously.

Because African doctors and other Health Care workers in Africa are familiar with Ebola - - health care workers generally didn't get infected in the past. With this strain health care workers are getting infected. Doctors are getting infected, nurses are getting infected.

Last but not least - before this outbreak became political (something the CDC wallows in) several African doctors had commented on how 'healthy' patients appeared almost up until their death. That's different - and telling.

" Longer good 'walking around' health" means statistics from earlier outbreaks are NOT valid. Older strains of Ebola took people down quickly - the sickness stopped them from being able to walk around and infect others. It was self contained for that reason.

No. You have your facts wrong.

patient zero was a 2 year old,
http://www.scientificamerican.com/article/patient-zero-believed-to-be-sole-source-of-ebola-outbreak/

and no, local physicians don’t have experience treating ebola...I worked in Liberia...

Ebola’s early symptoms are similar to other serious diseases such as flu, malaria, typhoid and measles... etc... until the bleeding starts.

no, local physicians don’t have experience treating ebola...I worked in Liberia...

My point was that the doctor's without borders person got ebola and he knew how 'not to get the disease'... a nurse working near him both came down with Ebola too. Both of them were experienced with the disease. I didn't mean to imply that all local doctors had worked with Ebola.

For the binary impaired: A value of 1 to 2 is a major concern. If 1 person can infect two then the following chart suggests just how fast every person on the planet can be infected.

1: 1
2: 2
3: 4
4: 8
5: 16
6: 32
7: 64
8: 128
9: 256
10: 512
11: 1,024
12: 2,048
13: 4,096
14: 8,192
15: 16,384
16: 32,768
17: 65,536
18: 131,072
19: 262,144
20: 524,288
21: 1,048,576
22: 2,097,152
23: 4,194,304
24: 8,388,608
25: 16,777,216
26: 33,554,432
27: 67,108,864
28: 134,217,728
29: 268,435,456
30: 536,870,912
31: 1,073,741,824
32: 2,147,483,648
33: 4,294,967,296
34: 8,589,934,592

That’s it: 34 replications and 8 billion people could have it. There is less than 7 billion people alive now.

This chart and the reality of the epidemic do not match.

Substitute influenza or chickenpox and I think you would see similar spreads of infection, maybe less.

The spread of Ebola is not on par with harder to get diseases like hepatitis.

Most strong disinfectants work but the government doesn’t name any specific brand.
http://www.cdc.gov/vhf/ebola/hcp/environmental-infection-control-in-hospitals.html

But the older web site for Africa suggests hand sanitzers or soap and water.
http://www.cdc.gov/vhf/ebola/prevention/index.html

Technical question: If the compounds used are to be used at higher than normal concentrations, as suggested on the CDC link provided, than that suggests the current “best practice” as labeled on the disinfectant compounds is not really the best practice, shouldn`t they now alter the standard recommended concentrations?

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