Statistical analysis
SAS 9.4 and Review Manager 5.3 software were used for analysis and data presentation. Continuous variables were represented by median and interquartile range (IQR). Classification variables were summarized as counts and percentages in each category. The age, gender, number and clinical signs of COVID-19 pneumonia patients were statistically described. Cochran-mantel-Haenszel test (stratified chi-square test) was used to compare the differences between severe and non-severe forms of COVID-19 pneumonia. With odds ratio (OR) as the effect size we used Mantel-Haenszel test with fixed or random effect for further meta-analysis of the clinical signs, and presented using the forest map. The study precision/bias was measured using the funnel plot.