Results from the microbiological analysis are recorded in a separate document only containing ID numbers. The analysis result will be assigned a code that designate patient ID nr (1,2,3...), Sample time (Pre- (0), 10 minutes (10) or 75 minutes (75) following disinfection.). The code will also contain information about leg randomization ((Drape (D) / No-drape (N)) and sampling site (Suprapatellar (S) / Infrapatellar (I)). All samples are plated in duplicate and an additional number will therefore be assign to identify the unique plate and the dilution step for the plate. The unique code is assigned to corresponding plate with sticker labels and will have a corresponding variable in the data entry form.