BACKGROUND: Reducing of COVID-19 transmission relies on controlling droplet and aerosol spread . Fluorescein staining reveals microscopic droplets . We used this technique to compare the droplet spread in a standard theatre (ST) and a laminar air flow theatre (LAF).
METHODS: We used a 'cough-generator' fixed to a theatre trolley at 45-degrees . Fluorescein stained 'secretions' were projected onto a series of calibrated targets . These were photographed under UV light and a 'source detection' software measured droplet splatter size and distance .
RESULTS: The smallest droplet detected was â 120 µm and the largest â 24,000 µm . We detected an average of 25,862 spots in the ST, compared with 11,430 in the LAF (56% reduction). The LAF mainly affected the smaller droplets (< 1000 microns). The surface area covered with droplets was : 6% at 50 cm , 1% at 2 m and 0.5% at 3 m in the ST; and 3% , 0.5% and 0.2% in the LAF respectively .
CONCLUSION: Accurate mapping droplet spread in clinical environments is possible using fluorescein staining and image analysis . The laminar flow affected the smaller droplets but had limited effect on larger droplets in our AGP cough model . Our results indicate that LAF require similar post-surgery cleaning to those of ST and staff should consider full PPE for medium and high-risk patients.