How Is Case Fatality Rate Calculated? Step-by-Step Guide for Students
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.
Factors Affecting Case Fatality Rate
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.
How to Calculate Case Fatality Rate?
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.
Difficulties in Calculating the Case Fatality Rate
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.
Case Fatality and Survival Rates
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.
Did You Know?
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.
FAQs on Case Fatality Rate Explained: Definition, Calculation & Importance
1. What is the Case Fatality Rate (CFR) and what does it measure?
The Case Fatality Rate (CFR) is a measurement used in epidemiology to determine the proportion of individuals with a particular disease who die from that specific disease. It is a key indicator of the severity or deadliness of an illness. A high CFR suggests that a large percentage of diagnosed cases result in death, signifying a more dangerous pathogen for those infected.
2. How is the Case Fatality Rate (CFR) calculated? Can you provide the formula and an example?
The Case Fatality Rate is calculated by dividing the number of deaths from a specific disease by the total number of confirmed cases of that same disease, and then multiplying by 100 to express it as a percentage.
Formula: CFR (%) = (Total deaths from disease / Total confirmed cases of disease) × 100.
Example: If a town reports 200 confirmed cases of a disease and 10 of those individuals die from it, the CFR is calculated as (10 / 200) × 100 = 5%.
3. What is the main difference between Case Fatality Rate (CFR) and Mortality Rate?
The primary difference between CFR and Mortality Rate lies in the population group being measured:
- Case Fatality Rate (CFR) measures the risk of death only among people diagnosed with the disease. Its denominator is the number of confirmed cases. It answers the question: “How likely am I to die if I get this disease?”
- Mortality Rate measures the risk of death from that disease for the entire population (both sick and healthy people) in a specific area and time frame. Its denominator is the total population. It reflects the overall impact of the disease on society.
4. Why is the Case Fatality Rate considered a measure of disease severity rather than overall risk?
The Case Fatality Rate (CFR) is a measure of severity because it isolates the outcome for individuals who are already confirmed to have the disease. By using the number of diagnosed cases as its denominator, it directly reflects the deadliness of the pathogen itself, independent of how widespread it is. The overall risk to a population (mortality rate) depends on both this severity (CFR) and how easily the disease spreads (transmissibility). A disease can be very severe (high CFR) but pose a low overall risk if it is very rare.
5. How does the Infection Fatality Rate (IFR) differ from the Case Fatality Rate (CFR)?
The key difference is the denominator used in the calculation, which reflects the completeness of infection data:
- CFR uses only confirmed, diagnosed cases. This often includes individuals who are sick enough to seek medical care and get tested.
- IFR attempts to use the total number of infected individuals, including those with asymptomatic or mild, undiagnosed infections.
Consequently, for any given disease, the IFR is almost always lower than the CFR because it accounts for a much larger pool of infected people.
6. What key factors can cause a disease's Case Fatality Rate to change?
A disease's CFR is not static and can vary based on several factors, including:
- Host Demographics: The age and overall health of the patient population. CFR is often higher in the elderly or those with pre-existing conditions (comorbidities).
- Healthcare System Capacity: The availability of hospitals, effective treatments, and trained medical professionals can significantly lower the CFR.
- Pathogen Variants: New strains of a virus or bacterium may be more or less virulent, directly impacting the CFR.
- Testing Strategy: If testing is limited to only the most severe cases, the CFR will appear artificially high. Widespread testing that captures mild cases will lower the observed CFR.
7. Why do some diseases like untreated rabies have a Case Fatality Rate near 100%?
The extremely high Case Fatality Rate of certain diseases is linked to their biological mechanism and the lack of effective treatment once symptoms begin. In the case of rabies, the virus attacks the central nervous system, causing progressive and irreversible neurological damage. Once clinical signs of the disease appear, there is no cure, and the condition is almost universally fatal. This inherent pathophysiology, combined with the absence of a post-symptomatic cure, results in a CFR approaching 100%.
8. Can a disease with a low Case Fatality Rate still be a major public health concern?
Yes, absolutely. A major public health threat is determined by both a disease's severity (CFR) and its transmissibility (how easily it spreads). A disease with a low CFR (e.g., below 1%) can still cause a massive number of deaths and overwhelm healthcare systems if it is highly contagious and infects millions of people. Therefore, public health officials must consider both the deadliness per case and the overall spread when assessing the risk of an infectious disease.
