superspreading

Superspreading refers to a situation in which an infected individual transmits an infectious agent to a disproportionately large number of secondary cases, compared with the average transmission rate in the population. The term is often used for events, called superspreading events, where a single person is responsible for many subsequent infections. In mathematical models, transmission is described as overdispersed, with a small fraction of cases generating most transmissions. This pattern is captured by a dispersion parameter k; small values of k indicate high heterogeneity in transmission, while large k indicates more uniform spread.

Several factors contribute to superspreading. Biological factors such as higher pathogen load or longer infectious periods can increase contagiousness. Behavioral and social factors include extended contact in crowded settings, poor adherence to infection control, and attendance at mass gatherings. Environmental conditions such as poor ventilation or indoor crowding can amplify transmission. The interaction of these factors means that standard averages like the basic reproduction number R0 may understate the risk posed by individual cases or events.

Superspreading has been observed in multiple diseases, including SARS, MERS, and SARS-CoV-2 (COVID-19). In many outbreaks, a minority of cases account for a majority of transmissions, and this pattern has shaped control strategies, emphasizing rapid case identification, contact tracing, isolation, ventilation improvements, and restrictions on large gatherings to prevent SSEs.

Public health implications include focusing on preventing SSEs rather than only reducing average transmission, and recognizing that reducing transmission in high-risk settings can disproportionately reduce the overall outbreak size. The concept highlights the role of heterogeneity in transmission dynamics and the importance of targeted interventions.