Epidemic curve

Epidemic curve is a statistical chart used in epidemiology to visualize the onset of a disease outbreak. It can help to identify the mode of spread of the disease, its time trend, and the population group most affected.

Definition

An Epidemic curve or "epi curve" is a histogram that displays the course of an epidemic by plotting the number of cases in a population over time. The horizontal axis represents the date or time of illness onset among cases, while the vertical axis represents the number of cases. Each bar in the graph represents the number of people who developed the disease at each point in time.

Purpose

The main purpose of an epidemic curve is to depict the distribution of cases over time. This can help to identify the mode of spread of the disease (whether it is person-to-person, common source, or vector-borne), the time trend (whether the disease is increasing, decreasing, or stable), and the population group most affected (by age, sex, or location).

Construction

To construct an epidemic curve, the following steps are typically followed:

1. Collect data on the number of cases and the date of onset of symptoms.
2. Plot the number of cases on the vertical axis and the date of onset on the horizontal axis.
3. Draw bars to represent the number of cases at each point in time.

Interpretation

The shape of the epidemic curve can provide clues about the nature of the epidemic. For example, a sharp upward slope followed by a gradual decline often indicates a common source outbreak, while a series of progressively taller peaks may suggest a propagated outbreak.

Limitations

While epidemic curves can be a useful tool in epidemiology, they also have limitations. They can only show the number of cases over time, not the severity or duration of the disease. They also cannot show the spatial distribution of cases, which can be important in understanding the spread of the disease.

See also

• Epidemiology
• Disease outbreak
• Histogram
• Public health

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  Epidemic curve of Hepatitis A, November-December 1978