Is a 21-Day Ebola Quarantine Really Adequate?

Natural News nutjob Mike Adams (a.k.a.
the self-styled Health Ranger) is certainly trying to fearmonger
the idea that 21-days is not enough. First, remember that this is
the guy who the FBI is investigating for surreptitiously setting up
a website earlier this year where he
likened crop biotech researchers to Nazis and then
argued…

…it is the moral right — and even the obligation — of human
beings everywhere to actively plan and carry out the killing of
those engaged in heinous crimes against humanity.

So consider the source when Adams writes:

A jaw-dropping report released by the World Health Organization
on October 14, 2014 reveals that 1 in 20 Ebola infections has an
incubation period longer than the 21 days which has been repeatedly
claimed by the U.S. Centers for Disease Control. …

This means that Ebola-infected U.S. citizens who are
“cleared” of Ebola may still erupt with the deadly virus for a
period of three more weeks. (emphasis his)

Why hasn’t anyone reported this until now? How is this not one
of the single most important pieces of information in the world at
this moment when all human life on our planet is now legitimately
threatened by an uncontrolled viral outbreak with a 70 percent
fatality rate and no recognized treatments or cures?

Adams is essentially putting his panicky spin on the World
Health Organization’s situation
assessment for Ebola in Nigeria and Senegal that states:

The period of 42 days, with active case-finding in place, is
twice the maximum incubation period for Ebola virus disease and is
considered by WHO as sufficient to generate confidence in a
declaration that an Ebola outbreak has ended.

Recent studies conducted in West Africa have demonstrated that
95% of confirmed cases have an incubation period in the range of 1
to 21 days; 98% have an incubation period that falls within the 1
to 42 day interval. WHO is therefore confident that detection of no
new cases, with active surveillance in place, throughout this
42-day period means that an Ebola outbreak is indeed over.

Presumably the WHO is also setting a 42-day time limit in order
to make sure that unaccounted for cases do not emerge before for
declaring an epidemic at an end.

Adams apparently thinks that people infected with Ebola who
remain asymptomatic for more than 21-days are somehow like modern

Typhoid Marys. This is wrong. Typhoid Mary was an asymptomatic
carrier of that bacterial disease, whereas people infected with
Ebola pass along the illness only after they become
symptomatic.

Those interested in less senational and more accurate coverage,
can go over to The National Journal, to read Brian
Resnick’s terrific article that asks, “Is
21 Days Enough for Ebola Quarantine?” Resnick is focusing on
calculations published in
PLoS Current Outbreaks by Drexel University researcher
Charles Haas who finds:

While the 21 day quarantine value currently used may have arose
(sic) from reasonable interpretation of early outbreak data, this
work suggests a reconsideration is in order and that 21 days may
not be sufficiently protective to public health.

Haas does importantly add:

The estimate of appropriate incubation time would need to
explicitly consider the costs and benefits involved in various
alternatives, which would incorporate explicit computations from
transmission modeling.

Let’s take a stab at roughly toting up the costs and benefits.
In a first scenario assume notionally that 20 people are infected
with Ebola and 19 become symptomatic before 21 days.
If they are placed in effective quarantine, the 19
will either die or get well in which case they are no longer a
threat to public health. What about the one who becomes symptomatic
after 21 days? There is no magic to the 21-day incubation period,
since an infected person who is symptom-free until 30 days or 42
days will anyway not be passing the disease on to anyone.
(Remember: No Ebola Marys.) Once the person whose incubation period
stretches beyond 21 days becomes symptomatic, he will presumably be
quarantined as well and like the others die or get well.

In the current epidemic in West Africa, the number of people to
whom each infected person passes the contagion on to is estimated
to be
around 2. In other words, each person ill with Ebola is now
infecting 2 people. To control an epidemic, the reproduction number
must fall below 1, at which point ever fewer people become
infected. In order to drive the reproduction number below 1 in West
Africa, it is estimated that 70 percent of infected people must be
quarantined.

Bear in mind that in unvaccinated and uninfected populations,
the effective reproduction
number for measles, whooping cough, smallpox, and polio is
estimated to be between 12-18, 12-17, 5-7, and 5-7 people
respectively.

So the 1 person out of 20 who becomes symptomatic after 21 days
will likely infect 2 people. The chance that these 2 newly infected
people will remain symptom-free for more than 21 days is also 5
percent. As you can readily see, the number of infected people who
remain symptom-free for more than 21 days declines steeply with
effective quarantine.

But let’s say that public health officials impose an even more
stringent quarantine. In this case, if 100 people merely suspected
of being exposed through casual contact (not body fluids) to Ebola
are quarantined for 21 days, presumably 95 of them would either
come down with the illness or show no symptoms. If quarantine
works, then those who come down with the disease would either
survive or die and the symptom-free will be released. In either
case, 95 of those who had been in quarantine would no longer be a
danger to the public.

What about the postulated 5 who become symptomatic after a
21-day quarantine? Aren’t they a menace to the public’s health?
Let’s begin by assuming that the 5 people who become symptomatic
(and thus contagious) after leaving quarantine come into contact
with 10 people each after their symptoms begin. I am postulating
this as a reasonable number of contacts after symptoms occur
because if the people who had been previously quarantined for 21
days due to possible exposure to Ebola are like me, they would be
obsessively monitoring themselves and run to a hospital quickly if
they feel ill. Although they were not in quarantine
(self-monitoring instead) both of the Dallas nurses who are now
infected with the virus basically did do this. Unfortunately, one
nurse who reported an elevated temperature was told not to worry
about it and flew off to Cleveland.  

In any case, my stringent scenario implies that 50 people
exposed to the folks who become symptomatic after 21 days would
subsequently be quarantined. Of the 50 people now in quarantine
perhaps 10 would be infected (reproduction rate of 2). The chance
that just one of the infected people now in quarantine would remain
asymptomatic until after 21 days is low (5% X 10 people = ½
person). But let’s assume the bad luck that one does become
symptomatic after quarantine and they too come into contact with 10
people. Of those 10 who are now in quarantine, assume that two are
infected. It becomes increasingly unlikely (5% x 2 people =
1/10^th person) that the infected would become
symptomatic after 21 days. And so on through subsequent stages of
quarantine.

Anecdotally, three missionaries with SIM USA were
quarantined for 21 days after being in contact with Ebola
patient Nancy Writebol who was flown from Liberia and successfully
treated at Emory University Hospital in August. None of them,
including her husband, came down with the disease. It is also the
case that the four quarantined
people who lived in the Dallas apartment with Liberian Ebola
patient Thomas Eric Duncan have so far not fallen ill. Their 21-day
isolation period ends this Sunday.

Finally, as Haas notes, deciding what limits to place on
quarantine come down to a benefit/cost judgment. At this point, the
21-day period for quarantine seems adequate for effectively
protecting public health.

For more background, see my article, “How
Cutting-Edge Medicine Might Have Spared Us the Ebola
Epidemic.”