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Superspreading and the effect of individual variation on disease emergence | Nature

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From Typhoid Mary to SARS, it has long been known that some people spread disease more than others. But for diseases transmitted via casual contact, contagiousness arises from a plethora of social and physiological factors, so epidemiologists have tended to rely on population averages to assess a disease's potential to spread. A new analysis of outbreak data shows that individual differences in infectiousness exert powerful influences on the epidemiology of ten deadly diseases. SARS and measles (and perhaps avian influenza) show strong tendencies towards ‘superspreading events’ that can ignite explosive epidemics — but this same volatility makes outbreaks more likely to fizzle out. Smallpox and pneumonic plague, two potential bioterrorism agents, show steadier growth but still differ markedly from the traditional average-based view. These findings are relevant to how emerging diseases are detected and controlled.

Abstract Population-level analyses often use average quantities to describe heterogeneous systems, particularly when variation does not arise from identifiable groups 1 , 2 . A prominent example, central to our current understanding of epidemic spread, is the basic reproductive number, R 0 , which is defined as the mean number of infections caused by an infected individual in a susceptible population 3 , 4 . Population estimates of R 0 can obscure considerable individual variation in infectiousness, as highlighted during the global emergence of severe acute respiratory syndrome (SARS) by numer

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