Typhoid outbreak following a picnic in California, 1916[54]We can therefore think of disease transmission as a continuum. At
one end, we have a situation where a single person – such as Mary
Mallon – generates all of the cases. This is the most extreme
example of superspreading, with one source responsible for 100 per
cent of transmission. At the other end, we have a clockwork epidemic
where each case generates exactly the same number of secondary
cases. In most cases, an outbreak will lie somewhere between these
two extremes.
If there is potential for superspreading events during an outbreak, it
implies that some groups of people might be particularly important.
When researchers realised that 80 per cent of transmission came
from 20 per cent of cases, they suggested targeting control measures
at these ‘core groups’. For such approaches to be effective, though,
we need to think about how individuals are connected in a network –
and why some people might be more at risk than others.
T in history was an academic
nomad. Paul Erdős spent his career travelling the world, living from
two half-full suitcases without a credit card or chequebook. ‘Property
is a nuisance,’ as he put it. Far from being a recluse, though, he used
his trips to accumulate a vast network of research collaborations.