Dynamic Changes in Viral Load and Intrapulmonary Inflammation on Imaging During COVID-19 Infection: A Single-Institution Cohort Study

Abstract

Background: Our study aims to determine the dynamic changes in viral load and intrapulmonary inflammation on imaging and to discern their relative relationship through a large sample cohort study of patients with severe and non-severe COVID-19. Methods: Intrapulmonary inflammation was quantified by a 72-point, semi-quantitative CT score, and viral load was measured using the cycle threshold (Ct) of nucleic acid specimens derived from the nasal and pharyngeal swabs of all the patients. The viral load and intrapulmonary inflammation were each staged according to fitted curves of the scatterplots. Findings: A total of 403 patients with 1716 CT scans and 729 nasal and 209 pharyngeal swab specimens were evaluated. For the viral load, the peak stage, descending stage, and plateau stage occurred at approximately 15 days, respectively. For intrapulmonary inflammation, the peak stage in severe and non-severe cases occurred at 14–37 days and 12–13 days, respectively. For nasal swabs, the median peak stage Ct values in severe and non-severe COVID-19 cases were 28.8 (25.9–32) and 28.5 (24.6–32.5), respectively, and the median plateau stage Ct values were 34.6 (31.6–37) and 35.0 (31.9–37), respectively. For pharyngeal swabs, the median peak stage Ct values in severe and non-severe cases were 28.5 (24.2–31.4) and 29.1 (25.1–31.3), respectively, and the median plateau stage Ct values were 34.2 (31.7–36.2) and 34.4 (32.9–37), respectively. The semi-quantitative CT scores during the median peak stage in patients with severe and non-severe COVID-19 were 22 (15–33) and 12 (6–19), respectively. The semi-quantitative CT scores were significantly higher (p < 0.001) in all of the stages in severe cases than in non-severe cases. The semi-quantitative CT scores were not significantly associated with the Ct values of nasal swabs (Pearson correlation = 0.089, p = 0.240) or pharyngeal swabs (Pearson correlation= 0.089, p = 0.551). Interpretation: The intrapulmonary inflammation observed in patients with non-severe COVID-19 reached the peak time faster, had a shorter peak stage compared to severe patients. The viral load peaked rapidly within one week after the symptom onset and then declined rapidly but underwent a long plateau stage in which viral load levels were close to normal. There was no significant correlation between viral load and grade of infection, but patients with severe COVID-19 had severe intrapulmonary inflammation. Funding Statement: This work was supported by Sanming Project of Medicine in Shenzhen (fund No:SZSM201612053). Declaration of Interests: The authors declare no competing interests. Ethics Approval Statement: This study was approved by the Ethics Committee of the Third People’s Hospital of Shenzhen, which waived the requirement for patient consent for this retrospective analysis.