Evaluation of nodule incidence as findings of lung involvement in Covid-19 infection and its comparison in three CT scan centers of Shiraz

Several typical and atypical findings have been observed in Covid-19 high-resolution computer tomography (HRCT). To our knowledge, there is no study investigating the relationship between the presence of nodules in Covid-19 patients and the patient's condition. Therefore, the present study assessed the frequency of pulmonary nodules in Covid-19 patients according to their condition.

This cross-sectional study assessed the medical images of the patients referred to three university-affiliated centers (Nemazi, Ali Asghar and Shahid Faghihi Hospital) to perform Covid-19 HRCT from April to September 2020. The centers have been named H1, H2, and H3. Patients who were referred to these centers had good, poor, and fair conditions, respectively. The history of patients was assessed carefully. Patients' demographic information, nodule shape, number, size, location, presence of cavitation, and GGO around the nodule were assessed and recorded.

Overall, 20576 patients (mean age=46.75±16.64 years old) were included in the study. Only 2.1% of cases had solid nodules. Most of them (96.76%) were accompanied by a GGO (halo sign), and only 10.42% were associated with a cavity. The good condition, patients showed significantly more solid nodules (3.46%) than others. In size of the nodules in good-condition patients (1.8 cm) is significantly larger than in fair-condition (1.22 cm) or poor condition patients (1.15 cm). 79.86%, 12.5%, and 7.64% of nodules were multiple, dual/triple, and single, respectively.

The frequency of nodules in the HRCTs of good-condition patients was significantly higher than in fair- or poor-conditionpatients; they also had more multiple and larger-sized nodules. The Pearson-coefficient test also revealed a small negative correlation between the presence of nodules and the patient's condition. It seems the presence of nodules indicates higher immunity to viral infections. In the follow-up, it was revealed that people who had nodules were not hospitalized in the ICU. Further study is needed to prove this point.