bookmark_borderMoving Forward

I have been remiss from making new posts, but I did not realize until I logged on today that it has been nearly a month since the last one.

The things I had wanted to post about became overwhelming as everything is so intertwined. I would begin writing about one topic (herd immunity, for example) and then find myself down a rabbit hole of other topics and then I felt stymied. As well, life intervened with a couple of new developments that needed attention.

Now, with areas in the country opening up, politics entering into an arena which should not be political (n.b., I do not kid myself that they haven’t been since the beginning of this crisis), and tensions running high across the country about a perceived dichotomy of choice (open now/hoax vs. lockdown forever/fear), I continue to ask: we have flattened the curve—we are working toward our new normal—what have we accomplished during the lockdown these past 11 (!!) weeks?

There has been progress—we know more about the SARS-CoV-2 virus and how it affects the body, we know more about how it transmits, we know more about how to treat cases, we know more about the potential for immunity, we have antibody tests, and we have many groups working on vaccines (even some under trial). This is pretty impressive progress—because the whole world is working towards a common goal.

But there is still so much more to learn. We are hearing reports about how the disease may affect children (albeit case studies). The CDC is saying the virus doesn’t spread easily from surfaces (but we must still remain cautious; contaminated surfaces are still a concern, just not the primary concern). Medical care for COVID-19 is evolving with the experience of the many doctors in our country who demonstrate that the practice of medicine is nuanced and an art, not neccessarily a methodology. We have treatments that are promising for severe cases; I am hopeful there will be treatments for less-severe cases that do not require hospitalizations (I will update this once I research that). We have evidence that there is an immune response and antibodies from the virus, and though there remains more to be learned about what level of immunity is conferred, this is promising for detecting people who have been infected previously (and were asymptomatic or mildly symptomatic) and a vaccine. Vaccines are under development, with some being tested. However, among approximately 200 antibody tests available on the market, as of this writing, 13 have been approved by the FDA for Emergency Use and even those will not tell us too much at this point (see CDC: EUA Authorized Serology Test Performance which also includes a good background on testing re: sensitivity, specificity, positive predictive value, negative predictive value and WebMD: Do I Need to Get an Antibody Test?). Lastly, as I mentioned before, a vaccine will not be a panacea—simply stated, just because a vaccine is available, it doesn’t mean we can snap our fingers and get adequate coverage—especially should immunity wane after 1-3 years.

An area which needs huge improvement is a commitment to bolstering and maintaining public health infrastructure. Public health is largely ignored and when it is needed—in times like this—it cannot function the way it should.

We have to learn how to live with this virus. We can. And we can do it without fear. But we have to be cautious.

So let’s figure that out.

The experts from all sectors within our country and globally must work together to come up with a plan to move forward into a new normal for at least the next few years. At the same time, we must continue our efforts for public health globally and at home. There will be another pandemic and we have to be ready for it.

bookmark_borderEpi 101: Mortality Rates and Case Fatality Rates

Since the beginning of this COVID-19 epidemic, the terms “mortality rate” and “death rate” due to the virus have been used in almost every article, op-ed, and scientific papers. Further, they have been used interchangeably to mean both “mortality rate” and “case fatality rate”. In epidemiology, however, these terms have specific meanings and we need to use them correctly to ensure clarity in communication.

In very simplified terms:

  • Mortality Rate = Death Rate for a POPULATION
  • Case Fatality Rate = Death Rate for total CASES

Mortality Rate (synonymous to Death Rate): This measure is a rate calculated on a population basis. The population could be defined for the world, a country, a state, or a specific community.

For a Mortality Rate, the number of deaths is the numerator, and the number of individuals in the population is the denominator, and is typically expressed as “per 100,000 population.”

Let’s look at the world, the US, and Sweden as examples to calculate mortality rates. From data accessed on May 5, 2020 from worldometers.info, we have:

  • World: 256,798 deaths/7,782,459,435 population
  • US: 71,548 deaths/331,002,651 population
  • Sweden: 2,854 deaths/10,099,265 population
  • World Mortality Rate: 3.3 per 100,000 population
  • US Mortality Rate: 21.6 per 100,000 population
  • Sweden Mortality Rate: 28.3 per 100,000 population

A mortality rate calculated in this manner is a Crude Mortality Rate. Note: While it is tempting to use crude mortality rates to compare different populations with each other, because mortality rates are highly associated with older ages, the mortality rates must first be Age-Adjusted. Age-Adjusted Mortality Rates take into account the different age distributions of a population.

Another erroneous use of “Mortality Rate” is when “Case Fatality Rate” is intended. To calculate a Calculate Fatality Rate (CFR), the number of deaths are in the numerator and the number of cases are in the denominator. Note: CFR actually is not a rate but a ratio as it is a proportion and not a rate.

With COVID-19, we have seen varied CFRs which is not unexpected given variations in the populations and the disease and incomplete data especially with the actual number of cases which makes it challenging to know the “true” CFR.

Given growing evidence for asymptomatic infection, Infection Fatality Rate (also a ratio) is also an interesting measure. With number of deaths in the numerator and the number of infected persons in the denominator. There are challenges to calculating this as well, especially with the current state of antibody testing and what the presence of (or lack thereof) antibodies actually means.

These different measures of death frequency—with other data, of course—for COVID-19 help give us important information with which to make medical, public health, and policy decisions.

For further reading on age-adjustment: See Age-Adjusted Rates – Statistics Teaching Tools from the New York State Department of Health