Transmission of communicable respiratory infections and facemasks

Yi Li¹, Yue Ping Guo¹, Kwok Ching Thomas Wong², Wai Yee Joanne Chung², Mayur Danny Indulal Gohel³, Hang Mei Polly Leung³

¹Institute of Textiles and Clothing, ²School of Nursing, ³Department of Health Technology and Informatics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR, China

Background: Respiratory protection efficiency of facemasks is critically important in the battle against communicable respiratory infections such as influenza and severe acute respiratory syndrome (SARS). We studied the spatial distributions of simulated virus-laden respiratory droplets when human subjects wore facemasks and were exposed to regulatory viral droplets by conducting in vivo experiments in facemask use.

Methods: Transmission pathway of aerosols of Fluorescein-KCl solution through facemasks and protective efficiency of facemasks were examined by using normal surgical facemasks and two facemasks with exhaust valves (Facemask A) and exhaust holes (Facemask B) covered with the same surgical filters situated at the back of the facemasks. Fluorescein-KCl solution was sprayed onto the faces of participants wearing the facemasks and performing intermittent exercises on a treadmill in a climatic chamber.

Results: Experimental results showed that when droplets spread onto a person face-to-face over short distances, 92.3% to 99.5% of droplets were blocked by the front surface of the facemask, whereas only 0.5% to 7.7% of droplets reached the back of the facemask. Both facemasks A and B had near or over 99% protection efficiency, compared with that of 95.5% to 97% of surgical facemasks. Using the same filters as normal surgical masks, facemasks A and B provided more effective respiratory protection against communicable respiratory infections such as influenza and SARS by the location of the breathing pathway to the back of the facemasks.

Conclusions: Separating the breathing pathway from the virus-contaminated area in facemasks can provide more effective protection against communicable respiratory infections such as influenza and SARS.

Keywords: transmission, communicable respiratory infections, separating the breathing pathway, the virus-contaminated area, facemasks with valves/holes, protective efficiency