2.4 Statistics
Statistical analysis was performed using SPSS 19 (IBM Corporation, NY, USA). The day of onset of symptom was set as day 0. The cumulative percentages of cases diagnosed by RT-PCR and CT as a function of time were plotted separately. Following initial positive RT-PCR, the cumulative percentages on first negative results and final negative results of follow-up RT-PCR were plotted as well. The CT scores of lung involvement were plotted over time. The cumulative cases diagnosed by RT-PCR and CT at different time points were compared by Chi-square test, two-tailed, and P <·05 was considered statistically significant difference, as well as for the comparison of chest CT features between cases with and without coinfection.