Thread by @fascinatorfun

Why do some COVID-19 patients infect many others, whereas most don’t spread the virus at all? | Science | AAAS

The lack of contract tracing especially in the 2 weeks prior to lock down was a huge missed opportunity to understand OUR clusters.
sciencemag.org/news/2020/05/w…

That missed opportunity (together with low levels of testing and inadequate isolation planning) not only resulted in an inability to break transmission threads but also robbed scientists & Gov of critical information it needs to plan an evidence based earlier easing of lockdown

Meatpacking plants, clubs, cruise ships, choirs, ski resorts, Zumba classes, nursing homes, prisons, churches, hospitals, live music venues, restaurants, residential conferences.

How handy it would have been during & after Cheltenham races if there had been vigorous tracing.

We would know a great deal more about disease transmission in crowded outdoor events, where people are shouting out and cheering, dashing inside to bars and restaurants, and staying in hotels and Air B&Bs.

What a lost opportunity.

And lives.

But is there some particular about the way SARS type virus transmit?

It seems likely that it is particulalry infectious through not just superspreaders who move across groups, but also superspreader events and venues.

Maybe most people don’t transmit but those who do in particular circumstances. So up pops the “k” number alongside the R number. The dispersion factor.

The Spanish Flu was not so much cluster driven. A ‘k’ of 1.

But SARS was cluster driven. A ‘k’ of 0.16
MERS. ‘k’ of 0.25

The lower the ‘k’ value the more clusters drive infection transmission. Not all epidemiologists agree on COVID19.

Both Bern Uni and Hing Kong estimated that the k value was higher than in SARS and MERS where they saw larger superspreader events.

But @AdamJKucharski of LSTHM estimates that the k value could be as low as 0.1. Lower than MERS and SARS.

MORE driven by superspreader events & clusters.

But given our contract tracing data has been so poor, due to lack of trained capacity I am not sure what data he has used

One theory is that, whilst transmission is mostly through droplets, aerosol Travis’s IoM of finer spray that hangs in the air for longer and drives larger clusters.

Some people shed virus for longer. Some expel more droplets.

Singing, activity leading to more exertion, loud environments causing voices to be raised all seem to play a part.

Some people are just more careful about personal hygiene, hand washing.

Indoor much more associated with transmission than outdoor. (Time of year? More indoor)

If the k value is as low as 0.1% then 10% of cases lead to 80% of the spread

However a Chinese epidemiological study suggested that 70% of transmission occurred in the family group

Maybe we’ll find out more (WITH high level contact tracing & testing) during warmer summer months

That 2-4 week period we missed here to find out more.

And we do need to guard against bias. Not just of memory but in contact tracers.

Not sure the Gov understands that a pre prepared list of questions being asked by inexperienced tracers rather drives bias.