What We Know (And Don’t) About
COVID 19
By Ken Karch, MPH
Updated September 1, 2020 Ver.9.0
(Updated material (since 7/15/2020) highlighted)
1.
Members of the
general public may be infected by droplet spread from other individuals;
there is little evidence that infection can come from animals such as pets,
except through intermediate contact with other persons who are infected (an
announcement several months
ago of an apparent COVID-19 case in a tiger at a Bronx (NY) zoo and two house
cats in New York are being investigated). There is evidence that the COVID-19
virus is a zoonosis (animal to human spread), and that the initial breakout
occurred from a bat population to humans thru a wild meat market or virology
lab in China. From there it apparently
found its way to other countries by person-to-person contact. There is
some evidence that the virus reached the US and spread prior to the generally
accepted date in early March, 2020.
2.
Droplets are
those which we are told have an effective distance of no more than 6 feet;
therefore, individuals are asked to maintain a social distance of 6 feet.
Recent studies have suggested that the virus does not easily spread to people
from surfaces.
3.
We do not know
whether fine, dry particles containing the virus can survive, and become
infective beyond a 6 foot distance. My MPH training indicated that the
effective distance of sneeze particles is 15 feet. Others have suggested that it may be up to 27
feet, or that the virus may be pervasive and infective throughout the general
atmosphere near a carrier…this is usually called aerosolized. There is some evidence that smaller virus
particles can be transmitted through normal talking or breathing, and in
particular in situations where lung air exchange is unusually high, such as
exercising and agitation. Smaller particles (less than 1 micron) are most
effective in entering the lungs. The
virus particles attach to lung membranes and create a reaction which damages
the ability of the lungs to function properly, causing difficulty in breathing,
inability to transfer oxygen, damage to other organs, and sometimes death. The definitions of direct transmission,
indirect transmission, droplet spread, and aerosolization are understood and
used differently by different people, particularly the media. Recent studies have indicated that the
COVID-19 virus is particularly susceptible to sunlight, moisture, and temperature.
Droplet spread diseases include the common cold, flu, meningococcal disease,
and rubella, while aerosol diseases include chickenpox, measles, and
tuberculosis.
4.
We are told that
face masks are effective, somewhat effective, or not effective by
different experts, that such protection varies with the materials from which
the mask is made, and the fit, and that the protection may be different between
outgoing vs. incoming infective agents.
General guidance from the CDC currently suggests that most face masks
may be somewhat effective in preventing or reducing infectious agents from
passing from the wearer to others, rather than from others to the wearer. Therefore, it requires a social commitment
of the potential wearer to protect others.
It is not clear whether all, many, some, or no potential wearers
understand this, or accept such a social contract. We have been warned of the risk that mask
wearers may be lulled into a false sense of security by wearing a mask,
and ignore other social distance recommendations. Beyond that, pop-up makers of cloth masks
tell you that cloth is the only reliable media for masks, and they try to sell
them as a protection for the wearer. Standards exist to measure the effectiveness
of face masks, with cloth masks about 50% effective in reducing virus particles,
provided they are properly worn and maintained.
Filtration studies
reveal that viruses are so small as to require adsorption as the filtration
mechanism, with moisture increasing the value of the filter until it breaks
down, collects live viruses (thereby creating an additional source of
infection), or plugs, which forces aerosols to escape around the mask. A recent study at Office Depot in Tacoma
indicated that about 15 to 35% of checkout customers were wearing face
coverings of many sorts; recent increases in availability and two recent orders
by the Governor mandating masks in retail establishments have raised that to
more than 99% by
September 1, 2020.
5. Although COVID-19 appears to infect all ages, we
know that elderly persons, and others with compromised immune systems,
and other underlying health conditions (which is poorly defined and quite
broad) have a greater risk of death, once they are infected. Typical case fatality rates (CFR) are at or
about 15% in those populations, and less than 5% in other populations. The CFR
from March 6 to March 10 in Washington State from the Kirkland care facility
was above 15%; since then it dropped to around 4% before rising slowly to 5.5%
by early May, then dropping slowly to about 2.6% on September 1. Deaths are a lagging indicator to
identified cases, so persons infected during the early March timeframe were
not dying until mid- to late-March. The same pattern emerged in Pierce County,
where the current CFR is about 2.2%, since rising to about 4% in mid-May from below 2% since
early March. Pierce County did not
experience an initial “bump,” and may have escaped the rapidly rising case and
death numbers experienced from Kirkland (which dominated the King County, State
of Washington, and even the US reported data for the first 10 days of March),
since social distancing and other measures were widely recommended before those
who would have been infected in early March would already have exhibited
corresponding death rates in late March. Beyond this, the reporting of
morbidity and case fatality rates is likely skewed due to decisions to address risks
to health care workers and those with symptoms or immune system issues (the
most likely to have the disease) first.
As a result, future morbidity and mortality rates may in fact drop
further.
6.
Efforts are
underway to increase the percentage of persons tested above the current (September 1, 2020) levels of 23%
and 18% (formerly 12.6% and 8.8% on July 15; and 5.1% and 4.4% on May
29) of the total population for the US and the State of Washington,
respectively. Pierce County had a 4.0%
tested rate on June 23, but ceased reporting this data on that date. Of those
tested, 7.7% and 5.1%
(formerly 8.2% and 5.9% on July 15; and 10.4% and 6.1% testing positive on May
29) of those tested positive in the US and the State of Washington,
respectively. Note that the data for
positive tests for the US as a whole differ between what the CDC reports (over
10%) and the Johns Hopkins database, from which other national and state
figures in this report are extracted. Again, Pierce County had a 6.6% positive
test rate on June 23, but ceased reporting this data on that date. Any of these
rates are well below the 50-60% thought by many to be needed to confer herd
immunity.
7.
A major jump in new
cases began in both the US and Washington State during the first week of
June, continued a steep increase to July 15, before following a gradual decline since July 15
through September 1. The July 15 7-day average new case data (about 67,000) was
much higher than the previous peak of about 31,000 for the US but has since dropped to about 42,000
on September 1; and for Washington State was also substantially higher (about 970 on
July 15 vs. 180 in late May), but has since dropped to about 460 on September 1.
8.
Case fatality rates (number of deaths divided by number of cases) rose to a peak during the
2nd and 3rd week of May in the US; the 4th
week of April in Washington State, and the 4th week of May through
the 2nd week of June in Pierce County, before dropping to about 3.1, 2.6, and 2.2
in the US, Washington, and Pierce County, respectively, on September 1.
The trend is downward, as one might expect as the number of tests in the
general population increases relative to the skewed sample early testing of
specially susceptible individuals and associated healthcare workers.
9. COVID-19 reported death rates fall disproportionately
among older persons and persons with other diseases or immune system
disorders. The “outbreaks” resulting in
COVID-19 deaths in this population are considered “premature deaths;”
and reduce the number of deaths of some fraction of the same persons from other
causes during the same or later time frames. To put it bluntly, if I die today
of something, I can’t die tomorrow of something else. Of the Pierce County
deaths reported as of July 15, 89% were over age 60, a cohort which constitutes
only 21% of the population. There
are recent challenges to the reported COVID-19 death rates, as only a fraction
appear to be exclusively, or primarily, COVID-19 deaths with influenza,
pneumonia, and other respiratory and non-respiratory diseases making large
contributing co-mortality.
10. We are told that the usual “incubation period”
of COVID-19 probably does not exceed 14 days (though some say it is longer),
but that a period of infectivity may begin before symptoms are apparent to the
infected individual or others, with infectivity being greatest in the middle of
the period (presumably something akin to a “bell-shaped curve”); and with greatest
infectivity in, say, the 6th to 10th day. We do not know how long the
period of infectivity lasts for those with and without symptoms.
11. The media has been full of reports, both positive
and negative, about the effectiveness and safety of various treatment
modalities, including those associated with hydroxychloroquine, azithromycin,
zinc, dexamethasone, and remdesivir.
12. We do not know whether persons who have contracted
the virus (and tested positive) and recovered, have acquired immunity for
future attacks of the same, or similar, viruses, or whether such immunity
may be short-term or longer term. Until
we acquire case and death data from a greater, and more representative,
proportion of the general population, we will be only guessing about herd
immunity. Beyond that, a debate exists between those who believe the proper
approach is to quarantine those who have been diagnosed with COVID19 or are
especially susceptible to it (a fraction of the population in the few
percentages of the total), and therefore allow herd immunity to develop among
the rest, a large fraction of whom will exhibit little or no symptoms in the
process (the examples of tour boat and military ship outbreaks are instructive
here). The arguers for this position say
the current efforts to quarantine virtually the entire population, with ensuing
economic, social, religious, and political impacts, will virtually assure that
a second and third harmonic of cases and deaths will occur, once restrictions
are lifted. There is mounting evidence that the new normalized case and death
rates in the US approach those of countries, such as Sweden, which did not
enact sweeping shut down requirements, and which greatly exceed those of others
who did (eg., Norway, Denmark, Finland).
There is also mounting evidence of “bumps” in new cases in those states
which opened prematurely (i.e., before meeting Federal guidelines). Major increases in cases
occurred leading up to July 15 in Florida, Texas, California, Arizona, and
Georgia, but all but California have seen a relatively steep downward trend to
September 1.
13. The role of government in requiring vaccination may
prove crucial in the future, once an effective, safe, vaccination protocol is
found. A case in point is the difference between the mandatory vaccination
laws governing childhood diseases (with some religious and other
exceptions, recently changed in Washington State law), versus the voluntary
flu vaccination recommendations. Lab results reported in the past few weeks
suggest that a vaccine protocol proof of concept in lab animals has been achieved,
and several vaccines have moved to the animal testing phase.
14. We do not know whether, or the extent to which, the
virus may mutate to other more (or less) dangerous forms. There is some
evidence that such mutations are not uncommon.
15. We know that COVID19 virus community episodes seem
to behave as other viruses and communicable diseases do, namely a logarithmic
growth phase, a leveling off period, and a decline. The slopes of the lines give the best
evidence of the place a community is in on the curve; the area under the curve
represents the total extent of the pandemic (classical differential and
integral calculus is in play here). This
is why we are urged to take necessary steps to “flatten the curve”
(thereby spreading it out in time to give more time to deal with shortages and
take other preventive and treatment steps). Flattening the curve implies we are
at the top of the number of cases (or deaths), and the public needs to
understand that a number of new cases (or deaths) perhaps nearly equivalent to
the numbers already experienced will be occur as the curve returns to near
zero. Beyond that, every new “bump,” such as that experienced in the past few
weeks, will increase the number occurring on the way back to “normal.”
16. The primary means of prevention, in the absence of
vaccination, is social distancing for communicable diseases. Daniel Defoe, in The Journal of the Plague
Year, in 1722, described the effectiveness of social distancing by recounting
the different results around London in 1665 between those who escaped the city
to country places, versus those who were forced (literally) to remain in
crowded dwellings with their families, often resulting in the death of the
entire family.
17. The future of the pandemic is largely unknown. It is complicated by the fact that we have
tested only about 18-23%
of the population; those tested are skewed toward health care workers and high
susceptibility persons; of those tested about 4 to 15% test positive; of those
testing positive, death rates range from 2 to 20%; we don’t know how many
asymptomatics are out there; we don’t know whether, when, and the degree to
which asymptomatics are shedding virus, or how long they will continue to do so;
nor the effectiveness of preventive measures such as social distancing and
masks; treatment modalities; or the potential effectiveness of vaccines. It is
further complicated by the fact that virtually all data comes in from 50 or
more different (e.g., state and local) agencies, each of which has its own set
of priorities, capabilities, and epidemic management plans (did someone say
something about herding cats?). We don’t
know the recovery rate of symptomatics or asymptomatics. We don’t know whether
asymptomatics secure immunity from future attacks. “Flattening the curve” of deaths will
follow “flattening the curve” of positive cases by some number of days, and
once the curves are flat, new cases and deaths will continue to follow while
the numbers return to near zero, and may very well equal or exceed cases and
deaths up to the “plateau” or “apex.”
Furthermore, relaxation of the prevention tools may result in a second
and third outbreak, as occurred in the 1918 flu epidemic and others.
18. As of July 15, between
4 and 5% of Pierce County residents had been tested, with a positive COVID-19
infection rate hovering between 6 and 7% of those tested, and the case fatality
rate between 3 and 4% of those testing positive. Total number of deaths (90) as
a proportion of Pierce County’s total population (about 880,000) is 0.1 per
1000 residents.
