ABSTRACT
OBJECTIVE: This study evaluated the differences in the appearance of COVID-19 pneumonia on chest computed tomography (CT) images of outpatient and cases that developed during hospitalisation. METHOD: Chest CT images of 66 patients (median age, 76 years; range, 29-94 years) who underwent the severe acute respiratory syndrome coronavirus-2 reverse-transcription polymerase chain reaction (RT-PCR) test were included in this retrospective study. The chest CT appearance was categorised as "typical," "indeterminate," "atypical," or "negative" in accordance with the recommendations of the Radiological Society of North America for COVID-19 pneumonia and compared among the following four subgroups: PCR-positive outpatient (n = 14); PCR-positive hospitalised (n = 7); PCR-negative outpatient (n = 9); and PCR-negative hospitalised (n = 36). FINDINGS: The frequency of "typical" findings in the PCR-positive outpatient cases (13/14, 92.9%) was significantly higher than that of those in the PCR-positive hospitalised cases (2/7, 28.6%, P = 0.022). There was no significant difference between the frequency of the "typical" appearance in PCR-positive hospitalised cases and that of those in the PCR-negative hospitalised cases (1/36, 2.8%, P = 0.192). CONCLUSIONS: When COVID-19 patients acquire infections while hospitalised, their chest CT images are less likely to show typical findings than those of outpatient cases. Comprehensive and careful assessments of CT findings and consideration of the possibility of concomitant infections with other pathogens and clinical information, such as underlying diseases, background lung structure, and time course of the infection, are required for the management of such cases.