Ebola Incubation period is 21 days?

[GreyGeek]

Dr. Frieden, in responding to reporter questions about why the US does not ban flights from West Africa into the United States, more than likely used a statement from a PLOS paper on Ebola which stated:

In addition, travel restrictions may hamper the deployment of personnel and support in the region, ultimately creating a counter productive effect in the containment effort.

The basis of that statement, as explained in a previous paragraph:

... assuming an 80% airline traffic flow reduction to and from the West African region  that provided evidence of a general time-delay of the distribution characterizing the probability of case importation of about three to four weeks.

The model doesn't investigate a 100% reduction of flow from West African regions.  And, it contains Dr. Frieden's second excuse for not imposing a 100% ban on travel from West Africa to the US:

In addition, travel restrictions may hamper the deployment of personnel and support in the region, ultimately creating a counter productive effect in the containment effort.

Again, that assumption is based on only an 80% reduction in air traffic flow out of West Africa to the US.
The article has an interesting graphic showing the mathematical model used for the argument above:

Code: [Select]

Even more interesting is the table of conclusions:
Transition parameters Value References
Mean duration of incubation period (1/?) 7 days 33,34,35
Mean time from onset to hospitalization (1/?h) 5 days 36
Mean time from onset to death (1/?d) 9.6 days 36
Mean time from onset to end of infectiousness for survivors (1/?i) 10 days 35,37
Mean time from death to traditional burial (1/?f) 2 days 10
Proportion of cases hospitalized, ? 80% 36
Rate of transition from infectious to hospitalized (?1) 0.67
Case fatality ratio, ? 55%
?1 0.54
?2 0.53
Mean time from hospitalizations to end of infectiousness for survivors (1/?ih) 5 days
Mean time from hospitalizations to death (1/?dh) 4.6 days


Those data are taken from actual West African Ebola cases.  The form of Ebola in the US may have mutated since these data were collected, but their "Mean duration of incubation period" of 7 days is a LOT LESS than that of 21 days given by the CDC.  WHO, on the other hand, reported 2 to 21 days.  If the "Mean" period of incubation is only 7 days then WHO is more correct in giving a range of 2 to 21 days.   A possibility of 2 days of incubation before being symptomatic decreases significantly the period between infection and infectiousness.   Since 12.7% do not present a fever during the infectious period it would mean that the onset of vomiting and other external symptoms would appear more rapidly and fewer people would be exposed.   That 12.7% of cases could only be detected by a blood or saliva test which, given current methods available at most hospitals, would require more than two days to complete and return results, unless expedited.


 

[shooter]

Grey Geek. can you translate that into English?

   you make my head hurt, 

  barbed wire, need more barbed wire,

[GreyGeek]

Sure.
The susceptible individuals are represented by S;
exposed individuals by E;
infected cases in the community by I;
hospitalized cases by  H; 
dead but not yet buried by F;
and individuals no longer transmitting the disease, R.

The set of S unexposed individuals and the set of exposed individuals,  (S,E),  are changed to (S-1, E+1) after another person is exposed.  The same pattern applies to the other seven sets.   
"Model parameters are:
?I , transmission coefficient in the community;
?H , transmission coefficient at the hospital;
?F , transmission coefficient during funerals.
?1 is computed so that ?% of infectious cases are hospitalized.
Compartment specific ?1 and ?2 are computed so that the overall case-fatality ratio is ?. The mean incubation period is given by ??1;
?h?1 is the mean duration from symptom onset to hospitalization;
?dh?1 is the mean duration from hospitalization to death;
?i?1 is the mean duration of the infectious period for survivors;
?ih?1 is the mean duration from hospitalization to end of infectiousness for survivors; and finally,
?f?1 is the mean duration from death to burial."

The first change, (S,E) --> (S-1, E+1) is described mathematically by:
(betaISI + betaHSH + betaFSF)/N 
(I use "beta" for that greek character because of limitations of this forum)
where N is the number of total cases in the model.  SI is the product of the number of uninfected people by the number of infected people and betaI is a conversion constant which computes the new total number of infected in that set.   Dittos for Hospitalized folks H and dead but unburied folks F.

The purpose of the division by N is to normalize the results, i.e., create a number between 0 and 1.0.   The result of the math is a conversion factor which enumerates how many exposed people will become infected in a population of S unexposed individuals  based on transmissions via infected I, hospitalized H and dead but unburied F.

The big take away is the set of "Transition Parameters", as I expressed in the paragraph beneath that table.  Essentially, Dr. Frieden was blowing smoke using a model which stated exactly opposite what he was claiming.

[Mali]

Greygeek,
 Although your second post did clear up some of the confusing parts in the first post, I have to join Shooter in asking for a  translation into common English. 

If I understand you correctly what you are ultimately saying is that NoBama and his "advisors" are ventilating particulated matter from their posterior orifices and we are being fed bovine excrement in mass quantities by those same people?

[GreyGeek]

ventilating particulated matter from their posterior orifices

Essentially, by relying on what we don't know or ignoring what we do know, like Shepard Smith did on Fox.

Since its appearance among humans in 1976 the Ebola virus has mutated several times.   There are five species of the genus Ebolavirus, and four of them are known to infect people.   There are cases of airborne transmission among animals, both in natural and controlled circumstances.   The CDC is relying on airborne transmission being "undocumented", not that it is impossible, when they say that Ebola can only be contracted through contact with bodily fluids.   Knowing how dishonest they've been in the past, and how they dissemble the data, one could easily come to the conclusion that they know about cases of airborne transmission of the four species, but are concealing that information.

The CDC discussion of the possibility of airborne transmission is here.   It mentions airborne transmission six times.

1 and 2)

Airborne transmission of Ebola virus has been hypothesized but not demonstrated in humans. While Ebola virus can be spread through airborne particles under experimental conditions in animals, this type of spread has not been documented during human EVD outbreaks in settings such as hospitals or households. In the laboratory setting, non-human primates with their heads placed in closed hoods have been exposed to and infected by nebulized aerosols of Ebola virus. In a different experiment, control monkeys were placed in cages 3 meters away from the cages of monkeys that were intramuscularly inoculated with Ebola virus. Control and inoculated monkeys both developed Ebola virus infection.

Monkeys are often used in modeling human diseases because their genetics and physiology is so similar to ours.  I leave it to the reader to decide if that modeling is valid when Ebola is the disease, or if various UN and American health agencies are revealing the full truth.   
3)

The authors concluded that “fomite and contact droplet” transmission to the control monkeys was unlikely, and that airborne transmission was most likely,

4)

A more recent experiment that was specifically designed to further evaluate the possibility of naturally-occurring airborne transmission of Ebola virus among non-human primates showed no transmission of Ebola virus from infected to control primates placed 0.3 meters apart in separate open-barred cages and ambient air conditions, but with a plexiglass divider that prevented direct contact between the animals.

5 and 6)

CDC infection control recommendations for U.S. hospitals, including recommendations for standard, contact, and droplet precautions for general care, reflect the established routes for human-to-human transmission of EVD and are based on data collected from previous EVD outbreaks in Africa in addition to experimental data. Airborne transmission of EVD among humans has never been demonstrated in investigations that have described human-to-human transmission although hypothetical concerns about airborne transmission of EVD have been raised

One thing for certain, N95 masks won't stop Ebola.   Could aerosols sprayed from the mouth of a coughing Ebola victim contaminate you if you inhaled them?




They say that you can only contract Ebola by contact with fluids from the victim.   Airborne fluids are fluids.  Large droplets go farther than small drops.  Drops landing on your face, face mask or body represent objected contaminated by an infected fluid.    As the droplets evaporate the virus is left floating around, jostled by Brownian motion.  These are the particles than can pass through an N05 mask.

Speculation:  Perhaps Pham and Vinson did maintain "protocol" but being in the room exposed them to airborne particles before the ventilation system purified the air?

N95 respirators made by different companies were found to have different filtration efficiencies for the most penetrating particle size (0.1 to 0.3 micron), but all were at least 95% efficient at that size for NaCl particles.

Hence the "N95" designation.   So, N95 masks can remove 95 out of every 100 viral particles between the ranges of 0.1 to 0.3 microns.  Ebola viruses have a diameter of 80 nanometers (80/1000 of a micron) and lengths can vary from sub micron to 14 microns.   All Firefighter / EMT/ Heavy Rescue & Haz Mat programs I've read about recommend N100 or P100 masks.    However, a mask does NOT a protocol make. What difference does it make if you wear the mask and then take it off before it is sterilized in place, before you touch it.  If you were to touch it with gloved (contaminated) hands you risk contaminating the exposed mouth and skin it covered.  If you remove your gloves your hands are exposed.   Your entire exterior clothing and mask must be decontaminated before you remove any layer, and more than one layer is recommended so that you can go through at least two stages of decontaminations.

All of this points out that the best practice is not buying hazmat suits and N100 masks, but keeping a large distance between yourself and infected people.  IOW, if you fear contamination or have been exposed then isolate your self along with safe supplies of food and water until at least 30 days since the last known infection has passed.   BTW, did you notice in the CDC article cited above that the Ebola virus was found in semen 101 days AFTER the last symptoms disappeared?  The article didn't say how long Ebola was detected in semen after the 101 days, but it did note that:

Sexual transmission of Marburg virus (but not Ebola virus) has been described. (in the literature)