The proportion of people who die from any particular disease amongst the people who suffer from that disease or are diagnosed with that disease over a certain period is known as the case fatality rate meaning when someone dies. In epidemiology, the case fatality rate is also known as the case fatality ratio or risk factor. Such rates help in predicting the disease course or the outcome of certain diseases known as prognosis. It also helps in assuming whether a disease is too severe or a meager one. Poor outcomes are a result of comparatively higher rates. When treatments improve, generally measure decreases. These rates also help in understanding the effect of new and upcoming treatments.
The fatality rate definition has already been stated above. The case fatality rate varies with time, population, and geographic areas. It is never constant. The rate highly depends on the host, the probable causing agent of the disease, and the environment depending on how they are interacting with each other. It also depends on the patient care available and the number of types of treatments available for the disease.
First, one needs to find out the number of deaths which has occurred from a particular disease over a fixed period. Next, considering the same period, one needs to find out how many people were diagnosed with that disease during that time. Finally, we divide the first value by the second one. The result will be the rate we need which is multiplied by 100 will give the percentage value.
The mortality rate slightly differs from this process of calculation. It is yet another measurement of death over a population shown throughout the turn. For both the calculations, the numerator is the number of total deaths. But in the case of the mortality rate, the denominator is the total number of risk deaths among the population in a certain period. It provides the measure of the risk of dying from a particular disease. Hence the fatality rate of dengue and mortality rate provides different information altogether.
One of the major drawbacks in calculating the case fatality rate is that one needs to determine the numerator and denominator with utmost accuracy. Suppose the period of disease lengthens for a particular disease from which a person is suffering. Then it is more likely that the person would not die due to that disease. Instead, they might die from some other cause. The case fatality rate can be easily overestimated if death from any other causes is counted in the numerator. On the other hand, if the death is not counted in the numerator due to some problems, then the case fatality rate will be underestimated. Generally, these rates are used to understand the behaviour of short-duration diseases or any acute or infectious disease. These are not used to understand long-term or chronic diseases.
The survival rate is the exact opposite of the case fatality rate. The dengue death rate is the number of people dying due to dengue within a particular time frame. This rate will eventually help to detect the future aspects of the disease and how medical intervention can affect it. The dengue death rate can further increase if proper medical treatment is not given or even if the prognosis is faulty. The fatality rate for dengue or any other surgery will start to depend on hospitalization days, complications of the operation, hours before the operation, year after the surgery to the entire life of the patient. One should mark the time frame or window within which the disease is being monitored. The survival rate is the exact opposite which states the portion of patients affected by a particular disease who are still alive within a particular time frame.
In 2019, the case fatality rate in Italy was around 7.2% while that in China was 2.3% during the Covid 19 outbreak.
For late-onset disease, the case fatality rate lies in the range of 1% to 6%. While for the early-onset disease it ranges from 3 to 10 percent.
The fatality rate is decreasing day by day due to advancements in medical science.
1. What is the Difference Between Mortality Rate and Case Fatality Rate? Explain With an Example.
Answer: Let us consider two kinds of population. At first let’s say, a population has around a thousand members. Let 400 of these people have a particular disease but around 100 of them died from the same disease and same time frame. Therefore, here the mortality rate is 100/ 1000 or 10% mortality rate. The other rate will be 100/400 or 25% case Fatality Rate. Let us consider the second population to be 1000 as well. Let 40 people suffer from a disease and 20 die from the same. Hence, the mortality rate will be 20/1000 or 2% and the fatality rate will be 20/40 or 50%. Hence the severity is greater in the second case. While death incidence is higher in the first population.
2. What is the Infection Fatality Rate?
Answer: The infection fatality rate is closely related to the case fertility rate as it applies to infectious outbreaks. But, it also calculates death proportions among all the affected people which includes all the undiagnosed and asymptomatic subjects. The main job of IFR is that it looks out for infections among healthy men. IFR looks for the Fatality rate of not only the sick but also those who are healthily infected. Those who have the disease detected as well as those who have the disease undetected or non-tested. There may be individuals who are affected but are not showing any symptoms. These people are known as inappropriate or subclinical. But, they can easily infect others. It is said that theoretically, IFR can never exceed the value of CFR.