Are we counting the wrong thing?
Mar. 21st, 2020 06:03 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
dreamsharkEveryone obsesses over calculating the death rate in pandemic diseases. I think a more meaningful statistic is the rate of severe and critical disease (where "severe" means roughly sick enough to need hospitalization and "critical" means you would probably die without intensive medical care). Not only is that the key thing we need to know as we desperately try to gear up our health systems to deal with the influx of patients, I think it is a more meaningful assessment of the actual seriousness of the disease.
Ebola used to be described as a disease with an 80-90% death rate, which it is in its native environment (isolated African villages with no hospitals). When recent outbreaks reached the cities, the death rate dropped to about 50%. That doesn't mean it's any less horrifyingly lethal a disease, it just means that with advanced supportive care in modern hospitals a lot of patients become critically ill, but eventually pull through.
Calculating the death rate after the fact can give you meaningful historical data, of course. Spanish Flu (1918) had a devastating effect on families and communities because somewhere between 2% and 5% of victims died. But if hospital care in 1918 had been similar to what we have today in this country, the death rate would have been much lower, perhaps no higher than "seasonal flu."
For comparison, the available data on COVID-19 is 5% critically ill and 15% severely ill but not critical. That's a hell of a lot of people hitting the hospitals. If the health system manages to keep up with that tsunami, most of those people will survive. If we end up with a health care system as overwhelmed as the one in northern Italy right now, the death rate will be much higher. That's what the governor of California was getting at when he dropped that 25 million number into a news conference on Thursday.
Ebola used to be described as a disease with an 80-90% death rate, which it is in its native environment (isolated African villages with no hospitals). When recent outbreaks reached the cities, the death rate dropped to about 50%. That doesn't mean it's any less horrifyingly lethal a disease, it just means that with advanced supportive care in modern hospitals a lot of patients become critically ill, but eventually pull through.
Calculating the death rate after the fact can give you meaningful historical data, of course. Spanish Flu (1918) had a devastating effect on families and communities because somewhere between 2% and 5% of victims died. But if hospital care in 1918 had been similar to what we have today in this country, the death rate would have been much lower, perhaps no higher than "seasonal flu."
For comparison, the available data on COVID-19 is 5% critically ill and 15% severely ill but not critical. That's a hell of a lot of people hitting the hospitals. If the health system manages to keep up with that tsunami, most of those people will survive. If we end up with a health care system as overwhelmed as the one in northern Italy right now, the death rate will be much higher. That's what the governor of California was getting at when he dropped that 25 million number into a news conference on Thursday.
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Date: 2020-03-22 01:27 pm (UTC)You know, at the pool party you were talking about the corona virus, and how you were concerned. And you said a whole bunch of really smart things, and some of them have been helpful as time went by. I just want to mention that you are very smart and perceptive, and I value that about you.
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Date: 2020-03-22 06:40 pm (UTC)I think that both death rate and rate of critical illness are important metrics, but that the latter is overall more meaningful. Another interesting metric that I have gleaned from the reporting is the moment when the number of cases that have completed their course exceeds the number of new cases reported. This is a tipping point in containment of a pandemic. South Korea hit that point on March 13. Astoundingly, that was LESS THAN A MONTH from their first reported case! If that's as meaningful as I think it is, that could mean that if the US continues the really aggressive containment efforts, we could be past the tipping point by mid to late April.
Interestingly, that is also the point at which death rate calculations become meaningful. There is still the iceberg problem - not knowing how many milder cases were not diagnosed. But you are past the problem where the deaths/cases formula is corrupted by the fact that the denominator is full of new cases for which the outcome is uncertain but the numerator contains only people who have already died. This results in a significant under count of the death rate.
An interesting metric related to number of tests is percent of tests that turn up positive. Obviously only meaningful within a limited sample with a similar set of criteria for testing, but still predictive. For instance, when Minnesota started getting batches of new test kits and began working on folks who were moderately sick but with no vector of infection, the number of positive results was about 2.5%. When the next batch of tests was processed, the percentage was similar.