Table of Contents
Fatality rate
- The Case fatality rate is the number of deaths divided by the total number of confirmed cases.
- Fatality= (Deaths/Cases) × 100
- The WHO estimates the fatality rate of the new coronavirus to be about 3%, based on current data.
MORTALITY
- Mortality represents the number of deaths per unit of population (100,000 now generally used and indicated)
- The population consists of the sick and the well.
- Mortality = Deaths/(Unit of population (sick and well)
Infection Fatality Rate
- Eventually, scientists hope to have a more comprehensive number called the infection fatality rate, which includes everyone who was infected with the virus.
- In other words, the case fatality rate describes how many people doctors can be sureare killed by the infection, versus how many people the virus kills overall.
Variations in Death rate
- In Italy, an epicentre of the outbreak, the death rate at the end of March stood at a 11%
- Meanwhile in neighbouring Germany, the same virus led to fatality rates of just 1%.
- In China, it was 4%
- Israel had the lowest rate worldwide, at 0.35%.
Why the difference?
- The same virus which doesn’t seem to have mutated significantly as it has spread has lead to widely differing reported mortality rates.
- Even within one country, the rate appears to change over time.
- Several factors account for the differences
- The most important is how we are counting, as well as testing, cases.
Testing
- Type A countries
- Test only patients with severe symptoms who will need hospitalization.
- No tests for the less-ill or asymptomatic cases
- The death rate can appear higher.
- Example – UK, Italy, Netherlands
- Type B countries
- Large scale testing of not only patients with symptoms but also all close contacts who are asymptomatic.
- The death rate can appear lower.
- Example – Germany, South Korea , Singapore
- It is necessary to test not just symptomatic cases, but asymptomatic people too.
- Having that data would give an accurate picture of how the pandemic is affecting whole populations, not just the sick.
Vo Village , Italy
- When the first Covid-19 case in Vò was confirmed, testing was rolled out to the entire village of 3,300 people.
- The results showed that at the time of the “first case”, 3% of the village was already infected, but showing no or few symptoms.
Counting the Deaths
- Some Health departments and agencies count all deaths as Covid-19 regardless of whether they were tested or if it was merely a suspected case of Covid-19.
- Italy counts any death of a patient who has Covid-19 as a death caused by Covid-19; so does Germany and Hong Kong.
- USA – Doctors have the discretion of classifying a death due to COVID19 or other reasons (heart attack or brain aneurysm).
- During an epidemic, doctors are more likely to attribute a death with complex causes as being caused by the disease in question – a trait known as ascertainment bias.
Health Infrastructure
- The number of hospital beds available could also play a role, as countries with lower capacity in their health services may have to start making decisions sooner about which Covid-19 cases to prioritise for treatment.
- This could lead to more Covid-19 deaths in the community that go untested (and uncounted), as people with symptoms stay away.
Age Profiles
- In 2019, nearly a quarter of the Italian population was 65 years or older, compared to only 11% in China.
- 90% of the Indian population is under 60.
- The percentages for the US, Spain and Italy are 79%, 75% and 71% respectively.
The LAG
- The number of cases from a few weeks ago will always be much smaller than the current one, so the true case fatality ratio will be higher.
Fluid numbers
- Determining death rates is especially challenging in the midst of a pandemic, while figures are necessarily fluid.
- Fatality rates based on comparing deaths, which are relatively easy to count, to infections, which are not, almost certainly overestimate the true lethality of the virus.
- Health officials and epidemiologists have estimated there are five to 10 people with undetected infections for every confirmed case in some communities
Swine flu Pandemic death rates
- H1N1 pandemic of 2009
- Early case fatality rate estimates were inflated by a factor of more than 10.
- 10 weeks into the epidemic, estimates varied widely between countries, coming in between 0.1% and 5.1%.
- When medics later had a chance to go through case documents and evaluate cases, the actual H1N1 case death rate was far lower, at 02%.