Clinical and population characteristics
We included 349 patients suspected of COVID-19 who underwent chest CT. Their clinical and demographic characteristics are resumed in Table 1. There were 136 patients with compatible CT signs of COVID-19 infection and 109 were RT-PCR positive (Figure. 1). The two positive and negative RT-PCR groups were comparable in term of age, sex and comorbidity rate. 73 of 109 patients (67 %) with positive RT-PCR had severe symptoms (severe pneumonia or ARDS as described above), presenting high rates of ICUH (35,7 %), invasive endotracheal ventilation (25,7 %) and death (10,1 %). Mean time interval between chest CT and RT-PCR was inferior to 1,5 days. Patients generally had chest CT the same day or the day after hospitalization and 6,2 days mean time after the first symptoms. Table 2 presents the chest CT signs of the 109 COVID-19 patients who had positive RT-PCR.
There were 34 patients with compatible COVID-19 CT, i.e. patients with negative RT-PCR but compatible chest CT. Despite repeated RT-PCR tests, 14 were considered as probable COVID-19 infection by physicians at the end of hospitalization, based on clinical assessment. 6,4 % of RT-PCR positive patients did not show COVID-19 CT signs (normal CT or not compatible CT signs). Typical chest CT signs in the 109 positive RT-PCR COVID-19 patients are described according to the delay between first symptoms and the first CT (Days 0 to 6, 7 to 14, and > 14) in Figure. 2. Maximum peak of CT signs was during the second week after the beginning of symptoms, in relatively similar proportions.