The effect of SARS-CoV-2 testing on healthcare-seeking behaviour at primary care level

Diagnostic self-testing for SARS-CoV-2 may lead to selection bias in test-negative case-control designs (TND) for COVID-19 vaccine effectiveness (VE) at the primary care level. We investigated whether SARS-CoV-2 self-testing among those with acute respiratory infection (ARI) after the acute pandemic phase was associated with primary care healthcare seeking in the general Dutch population.

We pooled questionnaire data from three study rounds (June 2022, November 2022, and April 2023) of the nationwide PIENTER Corona cohort study. Among 3152 participants aged ≥18 years, we selected the first self-reported ARI episode with cough, sore throat, dyspnoea, and/or coryza since March 2022. We performed log-binomial regression analyses adjusted for age, sex, education, and comorbidities to assess the associations between COVID-19 vaccination, SARS-CoV-2 self-testing, and general practitioner (GP) consultation, and between GP consultation and the prior self-test result.

Vaccinated (vs. unvaccinated) participants with an ARI episode more often self-tested [adjusted risk ratio (RR) 1.13, 95% confidence interval (CI) 1.04-1.27]. Vaccination (RR 0.78, 95% CI 0.48-1.44) and the self-test result overall (RR 0.86, 95% CI 0.69-1.08) were both not associated with GP consultation. However, with point estimates in opposite directions, vaccinated individuals seemed less likely (RR 0.86, 95% CI 0.68-1.08) and unvaccinated seemed more likely (RR 1.57, 95% CI 0.36-6.28) to consult a GP after a positive self-test.

Findings from this Dutch-population-based cohort suggest that GP consultations between March 2022 and May 2023 may have differed by self-test result and vaccination status, indicating that selection bias in the TND COVID-19 VE estimates from testing before GP consultation could be a valid concern. More research in various settings is needed.