What tests to use, when, why—and why not? Pitfalls of mass testing for COVID-19

“Concerns about hotspots flaring in schools of all types, sports teams, and workplaces lend special urgency to answering how best to limit the spread of COVID-19, and specifically how to test for and track the SARS-CoV-2 virus in the general population. An ongoing public health debate centers on whether we should use sub-optimal tests on a massive scale, testing frequently to overcome their analytical shortcomings.

The basic argument was encapsulated in the 9/11 Health Affairs post by Paltiel and Walensky and has two parts. First, that widespread screening will dramatically expand testing capacity and ease ongoing strain on critical supply chains. Second, that cases missed by sub-optimal tests are (probably) not infectious. In this Post, we address why these contentions ignore the serious consequences of false positive results, underestimate the importance of false-negative results, misapprehend the nature of supply chain failures in clinical laboratories, and ignore how over-reliance on biomedical tests results in risky public health behaviors.

[..] outbreaks demonstrate the concept and consequences of the “preventive misconception” – that individuals undergoing a preventive health intervention (in this case, screening) will engage in risky behavior because they assume they are not infectious – and that making this cognitive error is not rare.

[..] in low-prevalence populations, even using assays with outstanding analytical performance, half or more of all positive results will be erroneous. By comparison, false negative results are relatively rare – especially in the low-prevalence setting – even with insensitive (rapid) tests.

[..] False-positive SARS-CoV-2 results harm individuals, strain limited laboratory and public health resources, and risk long-range harm by undermining confidence in clinical and public health efforts.

[..] The case for high-frequency testing relies crucially on two assumptions: false-negatives will be detected on repeat testing 2-3 days later, and “false negatives” represent non-infectious people. Unfortunately, each of these assumptions is fatally flawed.

[..] Based on our experiences as Clinical Laboratory Directors, we anticipate that low-cost test alternatives like lateral flow assays and paper-based test strips will be subject to supply chain limitations similar to those we continue to experience with PCR assays. There is little evidence to support the notion that these alternatives will not have supply chain disruptions; to the contrary, preliminary findings from a survey of laboratory directors and infectious disease doctors conducted by the Infectious Diseases Society of America, along with lay reporting, demonstrate shortages extend far beyond COVID-19 testing supplies and threaten clinical laboratories’ ability to perform many different routine diagnostic tests.

[..] Testing for SARS-CoV-2 is important, particularly for diagnosing active infections, testing high-risk exposures, and targeted surveillance. However, mass testing, regardless of test quality is not necessary to achieve public health goals and could actually do harm. To effectively reduce the spread of COVID-19 we need wide-spread adoption of simple, cheap, collective public health policies: mask wearing, hand washing, and physical distancing (especially inside). High-frequency testing of asymptomatic populations may result in laxness practicing such key behaviors by engendering a false sense of security and paradoxically burden clinical laboratories and contact-tracing efforts.”

Full editorial, Lieberman JA, Lieberman SM and Bourassa LA. USC-Brookings Schaeffer on Health Policy 2020.10.27