The “K” Factor and EU and USA Cases

June 26th, 2020 by Tom Lynch

The K Factor

Ever heard of the “K” factor? Neither had I. But in yesterday’s Work Fitness and Disability Roundtable, Dr. Jennifer Christian’s long-running and valuable daily roundup of workers’ compensation medical news and musings, we were introduced.

Turns out the “K” factor could be tremendously important in helping leaders figure out how reopening the economy should proceed.

I thought Jennifer’s Roundtable post was so important I asked her if we could reprint it in the Insider. She gave permission, for which I’m grateful. So, here it is:

Hey, nothing like a fact-based “aha” to sharpen the mind and help point the way forward. A thought provoking article in New York Magazine (https://nymag.com/intelligencer/2020/06/coronavirus-meatpacking-plants-america-labor.html?utm_source=fb&utm_campaign=nym&utm_medium=s1&fbclid=IwAR0jnJXCeUx_zYVQuayha1XSMpMtjT-TSXIv7-RfIFNCDtlrz1hn558Da2w) on the reason for major differences between the COVID-19 experience in meatpacking industries in the USA and Europe brought up the “k” factor in the COVID-19 pandemic.  Ever heard of “k”?

Until yesterday, I hadn’t noticed (or paid attention to) any discussion about the implications for action of SARS-CoV-2’s  “k” factor. The “k” factor is an infecting organism’s observed dispersion behavior. Now is the time to start paying attention to the “k” factor because it points us straight to the main cause of the majority of COVID-19 cases: superspreading events in crowded indoor settings. We’ve all known that a lot of the cases have occurred due to spread on board ships, in prisons, hospitals, nursing homes, nightclubs and meatpacking plants – but to be truthful, I’m not sure we’d gotten the take-home message: SARS-CoV-2 is heavily dependent on crowded indoor spaces for its spread.

So, I did a bit more Googling and found a good Science Magazine article (https://www.sciencemag.org/news/2020/05/why-do-some-covid-19-patients-infect-many-others-whereas-most-don-t-spread-virus-all) that lays it all out quite clearly.  In addition to the R value (the mean number of subsequent new infections resulting from each infected individual), epidemiologists calculate how much a disease clusters. The lower k is, the more transmission is coming from a small number of people. The k value for the 1918 influenza pandemic was estimated at 1.0 – clusters weren’t too important. But during the 2003 SARS and 2012 MERS epidemics the vast majority of cases occurred in clusters, and their calculated k values were therefore low: 0.16 and 0.25 respectively.

In COVID-19, most infected people are not creating any additional cases. Adam Kurcharski from the London School of Hygiene & Tropical Medicine has conducted an analysis of COVID-19 dispersion and says, “Probably about 10% of cases lead to 80% of the spread.” A pre-print of his paper (https://wellcomeopenresearch.org/articles/5-67) has a calculated k value of COVID-19 at 0.1. Previous studies have pegged it just a tad higher than SARS or MERS.

There’s no point in trying to figure out which people are shedding the most viruses – though some of us clearly do disperse more bugs than others.  We professionals need to focus most of our attention on the places and types of events that SARS-CoV-2 needs in order to spread efficiently: loud and crowded indoor spaces, where people are cheek by jowl and raising their voices or breathing deeply: talking, singing, or shouting or aerobically exerting themselves. Ventilation and air flow in these settings also plays an important role.

Almost none of the clusters have resulted from outdoor crowded events.  Chinese studies of the early spread of COVID-19 outside Hubei province identified only one cluster among a total of 318 that originated outdoors. A Japanese study found that the risk of infection indoors is almost 19 times higher than outdoors. And here in the USA people who participated in (largely outdoor) Black Lives Matter protests have not been getting sick. (I also saw some data earlier saying that the virus is almost immediately disabled by sunlight.)

As the Science Magazine article says, the low k factor is …..”an encouraging finding, scientists say, because it suggests that restricting gatherings where superspreading is likely to occur will have a major impact on transmission, and that other restrictions—on outdoor activity, for example—might be eased.” So duh, let’s make the hierarchy of risk much more explicit. We need to make it crystal clear to the public (and patients and workers and employers) that the worst thing a person can do is participate in events in loud, crowded, and  indoor settings without rapid air turnover.

HOWEVER:  Many people are stuck. They live in crowded housing or congregate housing. The places where they live and work (ships, factories, office buildings, and medical facilities) already exist. People need to work, and winter is coming when we have to be inside.

I see this call to action: Are you, personally, confident that you are collaborating with all of the professionals whose input, cooperation, and contributions will be required? Think outside your silo. All of the various types of professionals who do event planning & commercial building design & engineering, industrial hygiene, HVAC, public health, and occupational health & safety need to join up and get deeply and rapidly involved in adapting / redesigning / re-configuring / re-engineering existing places and events to reduce the potential for superspreading.

A look at European Union and U.S. case statistics: Stunning

The following chart from the Johns Hopkins Tracker Project, printed in yesterday’s Statista Daily Alert needs no introduction or even analysis. It puts the period to Dr. Christian’s words.

 

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