What Is Case Fatality Rate and How Is It Calculated
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 in Epidemiology and Public Health
1. What is case fatality rate (CFR)?
The case fatality rate (CFR) is the proportion of people diagnosed with a particular disease who die from that disease within a specified period.
- It measures the severity of a disease.
- It is usually expressed as a percentage.
- It applies only to confirmed or diagnosed cases, not the whole population.
- Commonly used in outbreaks such as Ebola, COVID-19, and SARS.
2. How is case fatality rate calculated?
The case fatality rate is calculated by dividing the number of deaths from a disease by the total number of diagnosed cases and multiplying by 100.
- Formula: CFR = (Number of deaths ÷ Number of confirmed cases) × 100
- Example: If 50 people die out of 1,000 diagnosed cases, CFR = 5%.
- The time frame must be clearly defined for accuracy.
3. What is the difference between case fatality rate and mortality rate?
The case fatality rate measures deaths among diagnosed cases, while the mortality rate measures deaths in the entire population.
- CFR: Indicates disease severity among affected individuals.
- Mortality rate: Indicates the overall risk of dying in a population.
- Mortality rate is often expressed per 1,000 or 100,000 population.
4. Why is case fatality rate important in epidemiology?
The case fatality rate is important because it helps assess the severity and public health impact of a disease outbreak.
- Guides clinical management and treatment strategies.
- Helps compare the seriousness of different diseases.
- Supports public health planning and resource allocation.
- Used during epidemics to monitor disease progression.
5. Can case fatality rate change over time?
Yes, the case fatality rate can change over time depending on medical care, detection rates, and disease evolution.
- Improved treatment can lower CFR.
- Better diagnostic testing may detect milder cases, reducing CFR.
- Emergence of more virulent strains can increase CFR.
- Early outbreak data often overestimates CFR.
6. What factors affect the case fatality rate of a disease?
The case fatality rate is influenced by biological, healthcare, and demographic factors.
- Virulence of the pathogen.
- Availability and quality of medical treatment.
- Age and underlying health conditions of patients.
- Accuracy of case reporting and surveillance systems.
7. What is a high case fatality rate?
A high case fatality rate means a large proportion of diagnosed individuals die from the disease.
- Diseases like Ebola may have CFRs above 50%.
- Seasonal influenza typically has a low CFR.
- A high CFR indicates greater disease severity but not necessarily high spread.
8. Is case fatality rate the same as infection fatality rate?
No, the case fatality rate (CFR) measures deaths among diagnosed cases, while the infection fatality rate (IFR) measures deaths among all infected individuals, including undiagnosed cases.
- CFR: Based on confirmed cases only.
- IFR: Includes asymptomatic and unreported infections.
- IFR is usually lower than CFR.
9. What are the limitations of case fatality rate?
The case fatality rate has limitations because it depends on accurate case detection and reporting.
- Underreporting of mild cases can overestimate CFR.
- Delays between diagnosis and death can distort early estimates.
- Changes in testing policies affect calculations.
- It does not measure how contagious a disease is.
10. Can you give an example of calculating case fatality rate?
An example of calculating case fatality rate is dividing the number of deaths by confirmed cases and converting it into a percentage.
- If 200 people are diagnosed with a disease and 20 die:
- CFR = (20 ÷ 200) × 100
- CFR = 10%
- This means 10% of diagnosed patients died from the disease.
