COVID-19:  What can wildlife management teach us?

(Beth Clifton collage)

No,  it is not “shoot the victims”!

            SEATTLE––Perhaps the most startling statistic pertaining to the global spread of the COVID-19 coronavirus is the statistic almost nobody mentions:  the ratio of compensatory versus additive mortality.

What’s that?

It is not that as of March 10,  2020 there are still only about 140,000 COVID-19 cases of any degree of severity identified worldwide:  about the human population of Bellevue,  the Seattle suburb just south of Kirkland,  where 24 of the 29 COVID-19 fatalities in Washington state have occurred.

This is among about 1.7 billion people,  about 20% of the world’s population,  who may have already been exposed.

(Beth Clifton collage)

COVID-19,  drunk driving,  & diarrhea

Nor is the most startling statistic about COVID-19 that the death toll so far is barely 4,000 worldwide––fewer than the global toll for drunk driving over the same time––in the four months since the first cases appeared in the Huanan Seafood Wholesale Market in Wuhan,  China,  nearly four months ago.

Neither is the most startling statistic that only a little less than 5% of COVID-19 victims report having diarrhea among their symptoms,  which makes the run on toilet paper across the U.S. somewhat inexplicable.  Anyone with diarrhea is much more likely to have a common flu––or a rotavirus,  an even more frequent cause of diarrhea––than COVID-19.

Except among epidemiologists,  the ratio of additive versus compensatory mortality is not discussed much by medical doctors.  While medical doctors of necessity recognize that death is inevitable,  most tend to hold out hope that each individual patient can be saved,  at least for a little while longer,  if not actually in extremis.

Treating large numbers of people who are certain to die soon,  no matter what,  might otherwise be hopelessly depressing.

(Beth Clifton photo)

Calculating hunting seasons & bag limits

The ratio of compensatory versus additive mortality is,  however,  a familiar concept in wildlife management,  used most often to establish hunting season lengths and bag limits.

The ratio of compensatory versus additive mortality is also used by practitioners of neuter/return feral cat control to estimate how many cats need to be sterilized to balance kitten births with deaths in a colony.

In simplest terms,  “compensatory mortality” means the number of animals in any given population who may be expected to die of one cause or another during the time frame in question.

“Additive” mortality is deaths in a given population over and above the expected.

(Beth Clifton photo)

Carrying capacity (& hospital beds)

Wildlife managers trying to maintain a healthy deer population,  for instance,  try to estimate the percentage who will die each winter if the carrying capacity of the habitat is exceeded,  and then encourage hunters to shoot that number in the fall.

If the number of deer shot equals,  but does not exceed,  the number who might otherwise starve or die from other causes related to malnutrition,   the deaths of hunted deer will all be “compensatory,”  and the breeding population come spring will remain just about what it was during the preceding spring.

If more deer are shot than the number who would die otherwise,  the additional number of deer shot are “additive” mortality,  meaning that come spring the breeding population will be fewer.  If those survivors then fail to breed back up to somewhat more than the overwinter carrying capacity of the habitat,  the hunting bag limit will have to be reduced to avoid again exceeding the estimated number of compensatory deaths.

(Beth Clifton photo)

Fixing feral cats

Estimating the number of cats who will have to be sterilized to stabilize a feral colony begins with recognizing that each sterilization has the same effect on colony size as a death,  in that the sterilized cat is no longer part of the breeding population.

On average,  each feral female will bear four kittens per litter,  of whom one kitten will die before weaning and one more kitten will die before reaching reproductive maturity,  which among female kittens can be as early as five months of age.

Since about half of feral cat mothers live only long enough to bear one litter,  it is necessary to sterilize at least 70% for the effect of the sterilization campaign to become “additive,”  rather than compensatory,  in reducing breeding capacity.

(Beth Clifton photo/collage)

“Compensatory mortality” applied to COVID-19

“Compensatory” mortality in the case of COVID-19 means that if the victims were not hit by COVID-19,  their underlying health issues are such that they would likely die soon from some other cause.

“Additive” in this context means deaths in excess of expected mortality among the population falling ill with COVID-19.

The concept of “compensatory” versus “additive” consequences from COVID-19 also has application to calculating the numbers of hospital beds that victims will need.  If victims are already occupying beds in care facilities of various sorts,  their illnesses are “compensatory,”  because even without COVID-19,  they would be filling care space.

Only COVID-19 cases afflicting people who are not already in care facilities are “additive,”  contributing to a potential shortage of care facilities,  if the victims are more numerous than the buffer capacity that hospitals and other care facilities typically maintain to deal with disease outbreaks and local disasters,  such as bad multi-vehicle traffic accidents.

(Beth Clifton photo)

U.S. COVID-19 deaths all compensatory

In light of the “compensatory” versus “additive” ratio,  much of the international panic over COVID-19 overlooks the reality that the effects have so far been almost entirely “compensatory.”

For example,  all 29 COVID-19 deaths in the U.S. as of this writing have been compensatory,  and almost all of the confirmed COVID-19 illnesses for which data has been published.

Twenty-two of the 24 deaths in Washington state came among residents and former residents at the Life Care Center in Kirkland.  The other two deaths included a woman in her eighties who resided at the Issaquah Nursing & Rehabilitation Center and a man in his eighties who was a resident of the Ida Culver House in Seattle.

COVID-19 virus under a microscope.
(Beth Clifton collage)

Other deaths also in highest risk categories

Two more COVID-19 deaths have come in California,  two in Florida,  and one in Little Ferry,  New Jersey,  all among people in the highest risk categories.

Reported Jennifer Millman of NBC,   “The Little Ferry victim,”  right now the most recent, “was identified as John Brennan,  an employee of the Standardbred Owners Association of New York,  according to the group’s president in a Facebook post by Harness Racing Update. Health officials said Brennan had underlying conditions including emphysema,  hypertension and diabetes.”

This,  like all of the others,  was “compensatory” mortality.

(Beth Clifton collage)

Chinese mortality has been “compensatory” too

Examining the data from the first 1,023 of the more than 3,200 COVID-19 deaths occurring from China,  the Chinese Journal of Epidemiology on February 18,  2020 noted that “people with ages 80 and above,”  with the least life expectancy,  “had the highest case fatality rate of all age groups at about 15%.”

Further,  the Chinese Journal of Epidemiology observed,  “Patients with co-morbid conditions,”  meaning patients who were already ill,  “had much higher  fatality rates — 10.5% for those with cardiovascular disease, 7.3% for diabetes,  6.3%  for chronic respiratory disease,  6.0% for hypertension,  and 5.6% for cancer.”

By comparison,  the overall death rate from COVID-19 among males with confirmed cases was 2.8%,  and for females was 1.7%––a not surprising difference,  in view that approximately half of all adult Chinese males smoke tobacco,  with a significantly lower rate among women.  Among both Chinese males and females,  smoking is from two to three times as common as among Americans,  in all age ranges.

“No COVID-19 deaths have occurred among those with mild or even severe symptoms,”  the Chinese Journal of Epidemiology concluded.

(Beth Clifton collage)

Chinese infection rate falling fast

Reported Marjorie Pollack of ProMED-mail,  the online information exchange of the international Program for Monitoring Emerging Diseases,  on March 10,  2020:   “A total of 80,754 cases of confirmed COVID-19 have now been reported from China,  representing an increase of 19 cases in the past 24 hours,  of which 17 (89.5%) were in Hubei province,”  where the city of Wuhan is the provincial capital and is where the COVID-19 outbreak was first detected.

March 10,  2020,   Pollack continued,  was “the third consecutive day that the number of newly reported cases in a 24 hour period was less than 50.  Daily case counts less than 20,”  as reported on that day,  “were last reported in mid-January 2020,”  before person-to-person transmission was even identified and appropriate preventative measures were introduced.

(Beth Clifton collage)

Politicians don’t understand the math

Despite that encouraging news,  and despite the implications of little noticed ratio of compensatory to additive mortality,  elected officials including Washington governor Jay Inslee and New York City mayor Bill de Blasio joined many others in warning,  in the words that former Donald Trump administration Homeland Security adviser Thomas Bossert tweeted to Ken Dilanian of NBC,  “We are 10 days from our hospitals getting creamed.”

Obviously hospitals and other patient care facilities need to be taking preventive measures,  since they house the population most vulnerable to COVID-19.

Obviously,  as COVID-19 spreads to reach other people with severe underlying medical conditions who are not already in care facilities,  care facilities may be called upon to handle an influx of “additive” admissions.

Contrary to social media rumor, Marco Polo did not bring COVID-19 to Italy on a cruise ship.

Lessons from Wuhan & Lombardy

But a lesson might be taken from Wuhan,  which hastily built an entire hospital to accommodate local COVID-19 victims.  Within days of opening,  the new hospital was discharging more local patients than were admitted,  and began accepting patients from throughout Hubei province and even other nearby provinces.

A lesson might also be taken from Lombardy province,  Italy.

Reported Alessandro Speciale,  Daniele Lepido,  and Naomi Kresge on March 10, 2020,  for Bloomberg News,  “Lombardy, the region around Milan that accounts for more than a fifth of Italy’s economic output, is by far the worst-affected part of the country.  It has 5,469 cases,  including 440 in intensive care.

“More than 80% of the region’s 1,123 acute-care beds are dedicated to COVID-19,  after many other patients have been moved elsewhere and 223 extra places have been opened to cope with the emergency. About half of those are occupied,”  according to Lombardy health and welfare minister Giulio Gallera.

(Beth Clifton collage)

Lombardy alone has handled five times the U.S. case load

“As of now the region’s health care system is holding up well,”  Gallera said,  “but if the increase in the number of infected people in need of intensive care doesn’t slow down we could have issues.”

Meanwhile Lombardy,  with about 1/33rd of the human population and care facilities as the U.S.,  has already handled almost five and a half times as many COVID-19 cases,  and still has bed space,  if needed,  for as many more people in need of intensive care as are already admitted.

(Beth and Merritt Clifton)

Since the history of COVID-19 strongly suggests that by far the majority of new victims will be in the “compensatory” category,  mostly already in care facilities,  that will likely be sufficient––unless “additive” cases begin occurring.

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