Day 73: Super-Spreading

The world is at nearly 1,925,000 cases, with 119,000 deaths and 445,000 recovered. The standings haven't changed much, although Massachusetts (up only 5% today due in part to a change in reporting times) has moved up to third place in the US in a general scramble of the 20,000+ states. PlagueBlog wonders whether there is a strain difference going on, as our coronavirus strains are predominantly from the disaster area that is Europe, while the west coast, like Asia in general, seems to be doing far better with their direct-from-China strains.

A few other theories about the strange pattern of contagion involve super-spreaders. A preprint from March postulated compound super-spreading: Do superspreaders generate new superspreaders? a hypothesis to explain the propagation pattern of COVID-19, by Pablo M. Beldomenico in Argentina. He believes that a sort of cascade of super-spreading through high viral loads is what led to the heterogeneity of sudden outbreaks in places like Italy versus slow burns in places where you wouldn't expect them, like Japan. He brings in some evidence from experiments with veterinary diseases to bolster the high viral load part of the theory. He concludes thus:

If superspreaders generate new superspreaders by exposing susceptible people to large viral loads, this mechanism should be immediately acknowledged and considered in the responses being undertaken. In particular, emphasis should be placed on the isolation or strict distancing of people of risk groups, as they would not only have more chances of developing a more severe disease (with the potential of overwhelming the health system), but they could also be source of high viral loads.

The New York Times reports (some more) about the super-spreading event at Biogen, and the New Yorker reports on a super-skiing event in Idaho. (Viral loads are not documented.)

Let us not forget South Korea's infamous Patient 31. While there are other clusters in South Korea, hers takes the super-spreading cake. Back in the US, Channel News Asia reports on a man in Chicago who super-spread at a February funeral and a subsequent birthday party, infecting at least fifteen people and killing three. Note that the article suggests coronavirus could be more contagious than measles; it is not. Nothing is as contagious as measles, with an R₀ of about 15, and no one has suggested anything like that for COVID-19.

More on R₀ tomorrow...