Public's understanding of swab test results for SARS-CoV-2: an online behavioural experiment during the April 2020 lockdown

Objective Although widespread testing for SARS-CoV-2 is in place, little is known about how well the public understands these results. We aimed to provide a comprehensive overview of the general public's grasp of the accuracy and significance of the results of the swab test. Design Web-based behavioural experiment. Setting Italy during the April 2020 lockdown. Participants 566 Italian residents. Main outcome measures Participants' estimates of the SARS-CoV-2 prevalence; the predictive and diagnostic accuracy of the test; the behavioural impact of (positive vs negative) test results; the perceived usefulness of a short-term repetition of the test following positive or negative results; and rankings of causes for false positives and false negatives. Results Most participants considered the swab test useful (89.6%) and provided predictive values consistent with their estimates of test diagnostic accuracy and infection prevalence (67.0%). Participants acknowledged the effects of symptomatic status and geographical location on prevalence (all p<0.001) but failed to take this information into account when estimating the positive or negative predictive value. Overall, test specificity was underestimated (91.5%, 95% CI 90.2% to 92.8%); test sensitivity was overestimated (89.7%, 95% CI 88.3% to 91.0%). Positive results were evaluated as more informative than negative ones (91.6, 95% CI 90.2 to 93.1 and 41.0, 95% CI 37.9 to 44.0, respectively, p<0.001); a short-term repetition of the test was considered more useful after a positive than a negative result (62.7, 95% CI 59.6 to 65.7 and 47.2, 95% CI 44.4 to 50.0, respectively, p=0.013). Human error and technical characteristics were assessed as more likely to be the causes of false positives (p<0.001); the level of the viral load as the cause of false negatives (p<0.001). Conclusions While some aspects of the swab for SARS-CoV-2 are well grasped, others are not and may have a strong bearing on the general public's health and well-being. The obtained findings provide policymakers with a detailed picture that can guide the design and implementation of interventions for improving efficient communication with the general public as well as adherence to precautionary behaviour.

Automated summary

While most participants considered the swab test useful (89.6%) and provided predictive values consistent with their estimates of test diagnostic accuracy and infection prevalence (67.0%), they failed to take into account symptomatic status and geographical location in estimating the positive or negative predictive value. This highlights the importance of improving communication with the general public regarding the accuracy and significance of COVID-19 test results.