Statistical analysis
STERILE
The amount of bacteria in colony forming units (CFUs) were compared between different scenarios using Wilcoxon signed-rank test. When the CFUs were either 0 or 1 in each subject, the comparisons were made using McNemar’s test.The effect of each of the factors including: (1) the presence/absence of face masks; (2) the presence/absence of fenestrated sterile drapes; and (3) the types of drapes (reusable and disposable) was analysed. Different scenarios were grouped according to the above factors. In particular, the presence of face masks included scenarios 2, 5 and 7. The absence of face masks comprised scenarios 1, 4 and 6. The presence of fenestrated sterile drapes consisted of scenarios 4, 5, 6 and 7. The absence of fenestrated sterile drapes included scenarios 1 and 2. Reusable drape consisted of scenarios 4 and 5 and disposable drape was composed of scenarios 6 and 7. The bacterial CFUs were summed within group and compared between different groups.