Jennifer L Kasten, MD, MSc, MSc
A response to the video circulating by Drs. Dan Erickson and Artin Massihi on COVID-19 prevalence and immunity.
The two doctors, who own a chain of urgent cares in central California together, held a press conference where they announced the results of the testing they'd conducted and their interpretation of the data. Their take included political and economic recommendations based on their personal convictions, which will not be discussed here.
They made two epidemiology/immunology claims:
1) 340 / 5213 (6.5%) diagnostic tests were positive at their urgent cares. They conclude, scaling up, that 6.5% of the entire Central Valley is therefore positive. For Bakersfield, CA: it would mean about 58,000 people had the virus, far more than the nearly 700 confirmed cases. We should calculate mortality and morbidity (hospitalization, ICU) rates accordingly, they argue.
2) Prolonged social distancing damages the immune system, and we are all becoming weaker for staying at home.
MORE PEOPLE HAVE HEART ATTACKS AND BROKEN LEGS IN ERs THAN IN A SHOPPING MALL
Their fatal, immediate, obvious, rookie mistake is that their 5213 people are in NO WAY REPRESENTATIVE of the population at large. Although we don't know how many (because the data was not that thorough)- we can assume a decent chunk of these people had symptoms of COVID, sought care, and were tested. Their urgent cares had the lion's share of COVID tests for the entire Central Valley (which is awesome). So ANYONE in Bakersfield who felt worried would go there. Presumably doctors referred patients there whom they felt needed testing.
Walk around an ER on a Friday night. If 4 out of 50 patients had broken legs, and another 10 had heart attacks, you can't assume 8% of the city fell off a ladder when drunk that night and a full quarter were clutching their chest in an armchair as we speak. In epidemiology terms, that's selection bias- bias introduced by a non-random sample.
So, essentially their calculations are entirely invalid. If they could somehow prove that the 5213 were an entirely random sample of people which was perfectly representative of the age, sex, pre-existing conditions, ethnic background and degree of symptomatology of the Central Valley, that would be different.
UNLESS YOU LIVE INSIDE AN AUTOCLAVE, YOUR HOME IS PLENTY PATHOGEN-RICH.
The world is absolutely teeming with microbes. You're coated in them, your house is coated in them, they enter your body with every breath you take and everything you eat. Your immune system is getting a perfectly adequate workout. You're just restricting your exposure to a handful of things (respiratory pathogens) for a very short period of time.
The doctors have every unalienable right to express their personal views, but the evidence they offered to back those views up is invalid (and immunologically laughable). The Denominator is larger than the official case count (evidence for that discussed repeatedly on this page, and is now accepted dogma). Of course that will downwardly adjust the relevant rates. There's no need to hand-wave.