- Current Novel Coronavirus (COVID-19) Death Rate (case fatality rate or mortality rate) in the US, reported in the media is around 1-3% based on who is reporting or when it is being reported.
- In my opinion, it is impossible to calculate an accurate death rate (mortality rate) for COVID-19 in the US at this time. Here’s why!
Formula: Novel Coronavirus (COVID-19) Death Rate or Mortality Rate = Number of deaths due to COVID-19 till date (numerator) divided by Number of completed or closed cases (denominator).
Closed Cases: Completed or closed case means that the disease outcome has already been achieved (patients are either treated or recovered or discharged or dead). This is the number that should be used in the denominator of the above formula.
Active Cases: All this while, I think the “current number of total cases (active and closed cases)” is being used as the denominator in the above-mentioned. This is NOT right. Active case means, the patients are still actively infected, and a final outcome has not been achieved yet. Example: If there are 200,000 total cases in the US as of today, 20,000 of them are closed cases, and the other 180,000 are active cases. It may take 1-3 weeks more, for these active cases to achieve an outcome and then they become closed cases.
Concept of Outcome Lag Period:
- The number of COVID-19 deaths that occurred today is due to the COVID-19 cases from 1-2 weeks ago. The total active cases today will not result in an outcome until 1-2 weeks from today.
- If you are calculating the Novel Coronavirus (COVID-19) Death Rate today, you will use the number of deaths till date as of today in the numerator of the formula, however you cannot use the total number of cases (active + closed cases) today, in the denominator. Deaths today are due to the cases from a few weeks ago. Similarly, the current cases today will not result in deaths until 5-15 days from now. Hence, when you calculate the death rate, the deaths in the numerator should be matched with the closed cases from 1-2 weeks ago that resulted in these deaths.
- When the pandemic is still ongoing and the curve is on the rise (total daily new cases in the US are on the rise), the number of cases today is always significantly higher than the cases 1-2 weeks ago. Currently, the COVID-19 curve is rising upwards towards the apex. In this situation, the number of active cases today is always higher than the active cases yesterday. Hence, when you calculate the formula for death rate and use this higher number of active cases today in the denominator, this will result in the denominator being a higher number. This will in turn result in an inherent bias that artificially lowers the death rate, but in fact the real Novel Coronavirus (COVID-19) Death Rate is much higher.
Example with Real Stats:
Let us look at a sample situation in the US on 4/1/2020: The total number of deaths due to COVID-19 in the US until 4/1/2020 are 5,102 deaths. These deaths are not due the total active cases on 4/1/2020. In fact, these deaths are an outcome from the cases diagnosed approximately 7-10 days prior (3/22/2020 to 3/25/2020), that have closed (outcome has resulted). There is always a lag period between the case diagnosis and case outcome.
- Conservative Assumptions: For conservative calculations, let us assume that lag period is only 7 days i.e. on 3/25/2020, the total number of COVID-19 cases in the US were 68,211. If we use this number as the denominator, then the death rate would be 5102/68211 = 7.5% mortality rate.
- Non-conservative Assumptions: If we do a non-conservative worst-case scenario approach – lag period of 10 days: on 3/22/2020, the total number of cases were 33,592. This will put the death rate at 5102/33592 = 15% mortality rate.
- Overall Range: Based on this sample calculation on a cross sectional observation, the death rate (mortality rate) of COVID-19 could be estimated to be 7.5% to 15%.
Flaws of this Analysis:
- The above-mentioned example is by no means a thorough methodology. The numerators and denominators are always rolling numbers. They are dynamic. The lag between case diagnosis and case outcome is not a standard number. It can vary from 1 day to 21 days.
- In a perfect scenario, the denominator should only include closed cases. In the above example, the denominators include a sum of active and closed cases.
- The testing for COVID-19 has evolved over the last few weeks. In early March 2020, there were fewer tests, taking longer time to result. Currently we are having faster tests, and more quantity of testing.
- As we perform more tests over the next few weeks/months, a huge chunk of patients with mild symptoms that are currently not being tested due to limited testing, will be tested, and there will be more positives. This will increase the number of non-severe cases (denominator will be a higher number), thereby reducing the mortality rate numbers over the next few weeks/months.
- It is impossible to come up with an accurate Novel Coronavirus (COVID-19) Death Rate (mortality rate) at this time, based on the limited information available. We are currently in the pre-apex curve. We will have better information after we cross the apex, on the downhill slope.
- The current estimates of 1-3% death rates may be significantly lower than the actual death rates due to the above-mentioned reasons. However, the above methodologies I mentioned also has multiple flaws.
- A rough estimate of the actual death rates in the US, from COVID-19, could range from 5% to 15%.
- The idea of this blog post is not to cause concern or panic, rather put the word out there that the we probably do not really understand what this virus is capable of.
Why is No One Talking About This?
- I DO NOT KNOW. I was pretty alarmed when I calculated the stats and noted the above-mentioned findings. I immediately went to PubMed to check if any studies were published looking at the same concern.
- After 2 hours of deep dive, I found:
Who Am I? What is My Authority in this Topic?
- I am a Physician Scientist and I specialize in outcomes research. I am an Author / Principal Investigator of >100 peer reviewed research publications, published in NEJM, AJG, Gastroenterology, Medicine, Hepatology and other top medical journals.
- My research on Ebola viral disease was incorporated into U.S Department of Health and Human Services – ASPR TRACIE and NHS – NIHR. My research was incorporated into international guidelines and UpToDate.
- More information available here: LinkedIn
Just give it a thought!
Other sources used to gather data for this article: https://www.worldometers.info/