Statistical analysis
Quantitative variables as mean ± SD and qualitative variables also were reported as frequency (%). Chi-square and Fisher’s exact tests were used for categorical variable comparison. In addition, to compare the median of quantitative variables in the two groups test was used. Then, first to determine the factors associated with the positiveness of HRCT result univariate logistic model was fitted, and those variables which had P < 0.25 were entered into the multiple model. Receiver operating characteristic (ROC) curves were constructed to test the ability of final model to predict the positiveness of HRCT result. All analysis was carried out in the version 20.0 and STATA Release version 12. P<0.05 was considered statistically significant.