Background Current COVID-19 radiological literature is dominated by CT and a detailed description of chest x-ray (CXR) appearances in relation to the disease time course is lacking. Purpose To describe the time course and severity of the CXR findings of COVID-19 and correlate these with real time reverse transcription polymerase chain reaction (RT-PCR) testing for SARS-Cov-2 nucleic acid. Materials and Methods Retrospective study of COVID-19 patients with RT-PCR confirmation and CXRs admitted across 4 hospitals evaluated between January and March 2020. Baseline and serial CXRs (total 255 CXRs) were reviewed along with RT-PCRs. Correlation with concurrent CTs (total 28 CTs) was made when available. Two radiologists scored each CXR in consensus for: consolidation, ground glass opacity (GGO), location and pleural fluid. A severity index was determined for each lung. The lung scores were summed to produce the final severity score. Results There were 64 patients (26 men, mean age 56+/-19 years). Of these, 58, 44 and 38 patients had positive initial RT-PCR (91%, [CI: 81-96%]), abnormal baseline CXR (69%, [CI: 56-80%]) and positive initial RT-PCR with abnormal baseline CXR (59 [CI:46-71%]) respectively. Six patients (9%) showed CXR abnormalities before eventually testing positive on RT-PCR. Sensitivity of initial RT-PCR (91% [95% CI: 83-97%]) was higher than baseline CXR (69% [95% CI: 56-80%]) (p = 0.009). Radiographic (mean 6 +/- 5 days) and virologic recovery (mean 8 +/- 6 days) were not significantly different (p= 0.33). Consolidation was the most common finding (30/64, 47%), followed by GGO (21/64, 33%). CXR abnormalities had a peripheral (26/64, 41%) and lower zone distribution (32/64, 50%) with bilateral involvement (32/64, 50%). Pleural effusion was uncommon (2/64, 3%). The severity of CXR findings peaked at 10-12 days from the date of symptom onset. Conclusion Chest x-ray findings in COVID-19 patients frequently showed bilateral lower zone consolidation which peaked at 10-12 days from symptom onset.
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