Diagnostic performance of chest radiography in high COVID-19 prevalence setting: experience from a European reference hospital

Abstract

Purpose: The study's aim is to analyse the diagnostic performance of chest radiography (CXR) in patients with suspected coronavirus disease 19 (COVID-19).

Methods: We retrospectively considered 826 consecutive patients with suspected COVID-19 presenting to our emergency department (ED) from February 21 to March 31, 2020, in a high disease prevalence setting. We enrolled patients who underwent CXR and rhino-oropharyngeal swab for real-time reverse transcription-polymerase chain reaction (rRT-PCR). CXRs were evaluated by an expert radiologist; a second independent analysis was performed by two residents in consensus. All readers, blinded to rRT-PCR results, classified CXRs positive/negative depending on presence/absence of typical findings of COVID-19, using rRT-PCR as reference standard.

Results: We finally analysed 680 patients (median age 58); 547 (80%) tested positive for COVID-19. The diagnostic performance of CXR, interpreted by the expert reader, was as follows: sensitivity (79.0%; 95% CI: 75.3-82.3), specificity (81.2%; 95% CI: 73.5-87.5), PPV (94.5%;95% CI: 92.0-96.4), NPV (48.4%; 95% CI: 41.7-55.2), and accuracy (79.3%; 95% CI: 76.0-82.2). For the residents: sensitivity (75.1%; 95% CI: 71.2-78.7), specificity (57.9%; 95% CI: 49.9-66.4), PPV (88.0%; 95% CI: 84.7-90.8), NPV (36.2%; 95% CI: 29.7-43.0), and accuracy (71.6%; 95% CI: 68.1-75.0). We found a significant difference between the reporting sensitivity (p = 0.013) and specificity (p < 0.0001) of expert radiologist vs residents. CXR sensitivity was higher in patients with symptom onset > 5 days before ED presentation compared to ≤ 5 days (84.4% vs 70.7%).

Conclusions: CXR showed a sensitivity of 79% and a specificity of 81% in diagnosing viral pneumonia in symptomatic patients with clinical suspicion of COVID-19. Further studies in lower prevalence settings are needed.

Keywords: Pneumonia; Radiology/radiography.

Fig. 1

Patient flow chart. Out of the 826 consecutive patients who presented to the ED of our hospital between February 21 and March 31, 2020, 146 patients were excluded: 92 for not having clinical findings suspected of COVID-19 pneumonia, 50 because of the lack of rRT-PCR results and/or CXR, 4 because younger than 18

Fig. 2

Distribution of typical findings at CXR. This figure describes the percentage of true positive patients with involvement of a given area, virtually dividing each lung into six areas. Considering the right lung (R), 156 (36% of 432) patients showed involvement of upper external portions, 130 (30%) of upper medial, 291 (68%) of middle external, 233 (54%) of middle internal, 335 (78%) of lower external, and 323 (75%) of lower internal portions. Considering the left lung (L), 126 (29%) patients showed involvement of upper external portions, 92 (21%) of upper medial, 297 (69%) of middle external, 209 (49%) of middle internal, 324 (75%) of lower external, and 260 (60%) of lower internal portion

Fig. 3

Chest radiography findings in two confirmed COVID-19 patients. CXRs in AP projection of two different patients (A, B) show subpleural ground-glass opacities (arrows) in external middle and lower lung areas and interstitial reticular pattern in internal areas (arrowheads). Both CXRs were judged as positive for COVID-19 by the expert reader and by the less expert readers; both patients had positive rRT-PCR results

Fig. 4

Chest radiography of four different confirmed COVID-19 patients, obtained at admission to the emergency department. CXRs in AP projection (A–D) show bilateral lung involvement with typical radiological patterns of COVID-19 pneumonia including the presence of ground-glass opacities (arrow), interstitial reticular alterations (arrowhead), and extensive consolidations (asterisk). All CXRs were interpreted as positive for COVID-19 by the expert reader and by residents. All four patients had positive rRT-PCR results