Objectives To assess interobserver agreement and clinical significance of chest CT reporting in patients suspected of COVID-19. Methods From 16 to 24 March 2020, 241 consecutive patients addressed to hospital for COVID-19 suspicion had both chest CT and SARS-CoV-2 RT-PCR. Eight observers (2 thoracic and 2 general senior radiologists, 2 junior radiologists, and 2 emergency physicians) retrospectively categorized each CT into one out of 4 categories (evocative, compatible for COVID-19 pneumonia, not evocative, and normal). Observer agreement for categorization between all readers and pairs of readers with similar experience was evaluated with the Kappa coefficient. The results of a consensus categorization were correlated to RT-PCR. Results Observer agreement across the 4 categories was good between all readers (κ value 0.61 95% CI 0.60-0.63) and moderate to good between pairs of readers (0.54-0.75). It was very good (κ 0.81 95% CI 0.79-0.83), fair (κ 0.32 95% CI 0.29-0.34), moderate (κ 0.56 95% CI 0.54-0.58), and moderate (0.58 95% CI 0.56-0.61) for the categories evocative, compatible, not evocative, and normal, respectively. RT-PCR was positive in 97%, 50%, 31%, and 11% of cases in the respective categories. Observer agreement was lower (p < 0.001) and RT-PCR positive cases less frequently categorized evocative in the presence of an underlying pulmonary disease (p < 0.001). Conclusion Interobserver agreement for chest CT reporting using categorization of findings is good in patients suspected of COVID-19. Among patients considered for hospitalization in an epidemic context, CT categorized evocative is highly predictive of COVID-19, whereas the predictive value of CT decreases between the categories compatible and not evocative. Key Points • In patients suspected of COVID-19, interobserver agreement for chest CT reporting into categories is good, and very good to categorize CT "evocative." • Chest CT can participate in estimating the likelihood of COVID-19 in patients presenting to hospital during the outbreak, CT categorized "evocative" being highly predictive of the disease whereas almost a third of patients with CT "not evocative" had a positive RT-PCR in our study. • Observer agreement is lower and CTs of positive RT-PCR cases less frequently "evocative" in presence of an underlying pulmonary disease.

Objectives:To assess inter-observer agreement and clinical significance of chest CT reporting in patients suspected of COVID-19.Methods: From 16th to 24th March 2020, 241 consecutive patients addressed to hospital for COVID-19 suspicion had both chest CT and SARS-CoV-2 RT-PCR. Eight observers (2 thoracic and 2 general senior radiologists, 2 junior radiologists and 2 emergency physicians) retrospectively categorized each CT into one out of 3 categories (evocative, compatible for COVID-19 pneumonia, and not evocative or normal). Observer agreement for categorization between all readers and pairs of readers with similar experience was evaluated with the Kappa coefficient. The results of a consensus categorization were correlated to RT-PCR.Results: Observer agreement across the 3 categories was good between all readers (κ value 0.68 95%CI 0.67-0.70) and good to very good between pairs of readers (0.64-0.85). It was very good (κ 0.81 95%CI 0.79-0.83), fair (κ 0.32 95%CI 0.29-0.34) and good (κ 0.74 95%CI 0.71-0.76) for the categories evocative, compatible and not evocative or normal, respectively. RT-PCR was positive in 97%, 50% and 27% of cases classified in the respective categories. Observer agreement was lower (p=0.045) and RT-PCR positive cases were less frequently categorized evocative in presence of an underlying pulmonary disease (p<0.001). Conclusion:Inter-observer agreement for chest CT reporting using categorization of findings is good in patients suspected of COVID-19. Among patients considered for hospitalization in an epidemic context, CT categorized evocative is highly predictive of COVID-19, whereas the predictive value of CT decreases between the categories compatible and not evocative. Keywords Coronavirus infectionsAll rights reserved. No reuse allowed without permission.(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.