Study procedures
STERILE
The study was conducted in a closed air-conditioned room, used for everyday intravitreal injections at the Intravitreal Injection Clinic, Siriraj Hospital. The room was disinfected with UVC light (Philips UVC disinfection desk lamp 24W S TC) for 30 min before each subject. There were no specialized air filtration equipment or positive/negative pressure ventilation systems.In each experiment scenario, a subject was instructed to lie down flat on an injection bed. An investigator stood behind the head position of the bed while holding a blood agar plate for 2 min at the inferior orbital rim perpendicular to the face of the subject. The second investigator held a second blood agar plate, serving as an experiment control, 50 cm away from the subject, at the same height and in a similar orientation to the first plate. Both investigators wore N95 mask (3M™ Aura™ 1870+) and remained silent throughout the experiment. Prior to the experiment phase in each subject, a blood agar plate was placed at the head position of the bed for 2 min without people in the room to serve as a room condition control. All blood agar plates were sent for bacterial culture tests.Each subject was instructed to perform 7 experiment scenarios of using fenestrated sterile drapes and/or surgical face masks. The scenarios were the following: (1) no fenestrated sterile drape and face mask; (2) face mask only; (3) face mask with taping of the superior rim of the mask with adhesive paper tape (3M™ Micropore Tape 1530-1); (4) reusable fenestrated sterile cloth drape without face mask; (5) reusable fenestrated sterile cloth drape with face mask; (6) disposable fenestrated sterile drape without face mask; and (7) disposable fenestrated sterile drape with face mask. For all subjects, the face masks were worn tight fit to the nose (with the malleable nose bridge metal strip firmly pressed around the nose) and the openings of the fenestrated sterile drapes were centered over the right eye. Each scenario was performed in both silent and speaking conditions (14 scenarios in total). For speaking conditions, the subject was instructed to count consecutive numbers (in the Thai language) out loud for 2 min. The surgical face masks used in this study were disposable 3-ply face masks with ear loops and commercially available under the tradename Medimask (ASTM, F2100, level 1). The reusable fenestrated sterile cloth drapes (45 × 45 cm) and the disposable fenestrated sterile drapes (35 × 45 cm, polyethylene nonwoven sheet, Thai Gauze Co., Ltd.) contained the oval apertures of 35 × 50 mm. For each participant, the same mask and drapes were used for all of the 14 scenarios.To minimize carryover effects of each scenario to one another on the bacterial culture outcomes, the sequences of the scenarios were randomized for each subject prior to the experiments. The randomization first involved sequences of wearing/not wearing face masks and then sequences of covering/uncovering the faces with different types of sterile drapes. For each subject, the same randomized sequence was used for both silent and speaking conditions. Speaking scenarios were always performed after silent scenarios in every subject as speaking might cause more bacterial dispersion. There was a 2-min washout period in which the investigators all wearing N95 and remaining silent in the injection room between each scenario.All blood agar plates were sealed, labeled by anonymous code number and transferred to the Microbiology Laboratory at Siriraj hospital where they were incubated for 72 h at 37 °C in a 5% carbon dioxide–rich environment. The number of bacterial colonies per plate were counted using standard laboratory techniques by microbiologists. The bacterial species were identified using the conventional biochemical techniques of the Department of Microbiology, Faculty of Medicine Siriraj Hospital (test code 201201 bacteria: culture [aerobic]). The microbiologists were blinded to the experiment scenarios.