Spillover: the powerful, prescient book that predicted the Covid-19 coronavirus pandemic.

by David Quammen

While R0 (that important variable introduced to disease mathematics by George MacDonald) represents the average number of secondary infections caused by each primary infection at the start of an outbreak, a superspreader is someone who dramatically exceeds the average. The presence of a superspreader in the mix, therefore, is a crucial factor in practical terms that might be overlooked by the usual math. “Population estimates of R0 can obscure5 considerable individual variation in infectiousness,” according to J. O. Lloyd-Smith and several colleagues, writing in the journal Nature, “as highlighted during the global emergence of severe acute respiratory syndrome (SARS) by numerous ‘superspreading events’ in which certain individuals infected unusually large numbers of secondary cases.” Typhoid Mary was a legendary superspreader. The significance of the concept, Lloyd-Smith and his coauthors noted, is that if superspreaders exist and can be identified during a disease outbreak, then control measures should be targeted at isolating those individuals, rather than applied more broadly and diffusely across an entire population. Conversely, if you quarantine forty-nine infectious patients but miss one, and that one is a superspreader, your control efforts have failed and you face an epidemic.

On superspreaders