Super-spreader

A super-spreader is a host—an organism infected with a disease—that infects disproportionally more secondary contacts than other hosts also infected with the same disease. A sick human can be a super-spreader; they would be more likely to infect others than most people with the disease. Super-spreaders are thus of high concern in epidemiology, the study of the spread of diseases.

Some cases of super-spreading conform to the 20/80 rule, where approximately 20% of infected individuals are responsible for 80% of transmissions, although super-spreading can still be said to occur when super-spreaders account for a higher or lower percentage of transmissions. In epidemics with super-spreading, the majority of individuals infect relatively few secondary contacts.

Super-spreading events are shaped by multiple factors including a decline in herd immunity, nosocomial infections, virulence, viral load, misdiagnosis, airflow dynamics, immune suppression, and co-infection with another pathogen.

Although loose definitions of super-spreading exist, some effort has been made at defining what qualifies as a super-spreading event (SSE) more explicit. Lloyd-Smith et al. (2005) define a protocol to identify a super-spreading event as follows:

This protocol defines a 99th-percentile SSE as a case which causes more infections than would occur in 99% of infectious histories in a homogeneous population.

During the 2003 SARS outbreak in Beijing, China, epidemiologists defined a super-spreader as an individual with transmission of SARS to at least eight contacts.

Super-spreaders may or may not show any symptoms of the disease.

Super-spreaders have been identified who excrete a higher than normal number of pathogens during the time they are infectious. This causes their contacts to be exposed to higher viral/bacterial loads than would be seen in the contacts of non-superspreaders with the same duration of exposure.

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