Create Date: October 15, 2024
Last Modified Date: February 13, 2025
Incidence rate is calculated with the following variables:
When using this tool, you input the total number of new cases of the disease along with the population at risk. The resulting incidence rate tells you how many individuals are affected by the illness per a given number of people (e.g., per 10,000 people). This is crucial for understanding the spread and potential impact of diseases, particularly during outbreaks or epidemics.
Our incidence rate tool is very easy and simple to use. Follow these steps to use the calculator:
Let’s say there are 200 new cases of an illness in a population of 50,000 people. To find the incidence rate per 10,000 people, you would input these values, and the result would be 40. This means there are 40 new cases per 10,000 people, then if we change the per 10,000 people to another option such as the per 1,000,000 people the answer is converted to be 400.
Incidence rate is a more modern term and a concept that is rather new compared to being old. Its roots do not go back thousands of years. While ancient civilizations may have detected patterns with diseases spreading, the thought of a metric like incident rate was never talked about until much later in history.
Arguably the first major step in taking diseases and tracking their spread very seriously came with the bubonic plague in 1347. With massive numbers being affected, deaths would be tracked and counted as best as they could, this is the first real step towards caring about this type of information.
Another major step was when John Snow, a British physician, tracked the spread of Cholera in London. He would map out the cases and calculate the number of new infections per population, making it an early version of incidence rate.
With science continuing to advance, the early 1900s would introduce the category of epidemiology. Soon after, the International Classification of Diseases (ICD) would standardize disease tracking worldwide. By the mid 1900s, the mathematical formula for incidence rate would be introduced and welcomed.
Simply put, incidence rate describes how quickly disease occurs or spreads in a population. This can be useful for personal safety and for planning mitigation measures to limit spread.
A high incidence rate indicates that the disease or illness is spreading quickly, suggesting a greater likelihood of new individuals contracting the illness within the population.
A low incidence rate means that fewer new cases are being reported relative to the population at risk, suggesting that the spread is under control or not very rapid.
Understanding incidence rate can be difficult if some of the terms and keywords used are not ones you understand. Here we shed some more light on some of these terms.
| Term | Definition |
|---|---|
| Cases | Each time a person is infected with a disease or ailment that is a new case. |
| Epidemiology | The study of infectious diseases. |
There are many interesting things that can be shared about incidence rate. Here are some of our favorites.
In 1854, London physician John Snow tracked a deadly cholera outbreak using incidence rates. He noticed cases were concentrated around a single water pump. By comparing the incidence rates in different areas, he proved contaminated water, not bad air, was the cause.
In the 1950s, British researchers Richard Doll and Austin Bradford Hill discovered that smokers had a lung cancer incidence rate 20 times higher than non-smokers.
The 1918 Spanish Flu infected an estimated 500 million people, but the actual incidence rate was likely much higher.
