The evolving usefulness of the Test-Negative Design in studying risk factors for COVID-19 due to changes in testing policy

TL;DR

This paper discusses how the Test-Negative Design's usefulness in studying COVID-19 risk factors has evolved due to changing testing policies, highlighting new research opportunities and methodological considerations.

Contribution

It extends previous work by analyzing how shifts in testing criteria enable separate investigation of infection risk and disease risk factors.

Findings

Changed testing policies allow differentiation between infection and disease risk factors.

New testing contexts provide opportunities for more nuanced epidemiological analyses.

Methodological considerations are necessary for accurate interpretation of test-negative studies.

Abstract

This paper is a short extension of our previous paper [arXiv:2004.06033] about the use of the Test-Negative design to study risk factors for COVID-19 [See: PubMed and ArXiv reference below] Reason for the extension is that the conditions under which people refer themselves for testing have greatly changed: originally, in most countries priority was given to people with symptoms, but nowadays people without symptoms are also tested for different reasons, e.g., during contact tracing, or to be allowed on an (international) flight. Interestingly, this opens new possibilities to separately investigate risk factors for infection and risk factors for becoming diseased. To use this new situation to best effect, one has to think carefully about how to elucidate the different reasons for testing and what analyses one might do with the different groups.