Serial interval

Serial interval is the time period between successive cases in a chain of transmission. It is a key parameter in understanding the spread of infectious diseases. The serial interval can be influenced by several factors, including the nature of the pathogen, the mode of transmission, and the susceptibility of the population.

Definition

The serial interval is defined as the time from onset of symptoms in a primary case to onset of symptoms in secondary cases. This is different from the incubation period, which is the time from exposure to onset of symptoms. The serial interval can be negative if the secondary case shows symptoms before the primary case.

Factors influencing the serial interval

The serial interval can be influenced by several factors:

• Pathogen characteristics: The nature of the pathogen, including its incubation period and infectious period, can influence the serial interval. For example, pathogens with a short incubation period and long infectious period may have a shorter serial interval.

• Mode of transmission: The mode of transmission can also influence the serial interval. For example, airborne diseases may have a shorter serial interval than sexually transmitted diseases.

• Population susceptibility: The susceptibility of the population can also influence the serial interval. For example, in a population with high immunity, the serial interval may be longer as it takes longer for the pathogen to find a susceptible host.

Importance in epidemiology

The serial interval is a key parameter in epidemiology. It is used to estimate the reproductive number (R0), which is the average number of secondary cases generated by a primary case. The serial interval can also be used to estimate the growth rate of an epidemic and to predict its future course.

See also

• Incubation period
• Infectious period
• Reproductive number
• Epidemiology

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