Transmission of communicable respiratory infections and facemasks

Abstract

Background:Respiratory protection effi ciency of facemasks is critically important in the battle against communicable respiratory infections such as infl uenza 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 effi ciency 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 fi lters 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 effi ciency, compared with that of 95.5% to 97% of surgical facemasks. Using the same fi lters as normal surgical masks, facemasks A and B provided more effective respiratory protection against communicable respiratory infections such as infl uenza 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 infl uenza and SARS. Keywords: transmission, communicable respiratory infections, separating the breathing pathway, the virus-contaminated area, facemasks with valves/holes, protective effi ciency IntroductionAn infl uenza pandemic has the potential to cause more death and illness than any other public health threat (DHHS 2005). Since January 2004, a total of 240 human cases of avian infl uenza A (H5N1) have been reported to the World Health Organization (WHO) and of these cases, 141 were killed by H5N1 (WHO 2006). Therefore, Monto (2005) pointed out that the greatest concern is that human-to-human transmission may begin if there is a change in the vital genome of avian infl uenza.The main way that infl uenza viruses are spread is from person to person via virus-laden respiratory droplets (particles with size ranging from 0.1 to 100 µm in diameter) that are generated when infected persons cough or sneeze (Roy and Milton 2004; CDC 2006). These respiratory droplets can then be directly deposited onto the mucosal surfaces of the upper respiratory tract of susceptible persons who are near (ie, within 3 feet) the droplet source such as healthcare workers (HCWs) in healthcare environments. Therefore, it is recommended that healthcare personnel use a fi t-tested respirator, at least as protective a...

Face Mask Use in the Community for Reducing the Spread of COVID-19: A Systematic Review

“…Table 1 reports characteristics of the included studies. Of the 35 included studies, three were cluster-RCTs ( 32 , 33 , 35 ), two cohort studies ( 38 , 41 ), four were case-control ( 47 , 51 , 62 , 64 ), four cross-sectional ( 34 , 46 , 49 , 60 ), 13 were quantitative-deterministic predictive models ( 11 , 13 , 36 , 39 , 40 , 42 , 43 , 45 , 55 , 57 – 59 , 63 ), and nine were laboratory experimental studies ( 37 , 44 , 48 , 50 , 52 – 54 , 56 , 61 ).…”

Droplet Exposure Risk to Providers From In‐Office Flexible Laryngoscopy: A COVID‐19 Simulation

“…The safety and efficacy of similar designs in quantifying droplet splatter for endonasal and other otolaryngologic procedures are established in the literature. 5-10…”

Reply to the comments on “in vivo protective performance of N95 respirator and surgical facemask”

“…Sound scientific evidence needs to be obtained to reveal whether the respirator filter is designed properly to ensure that airborne and/or droplet particles are captured during inhalation through the filter. That is why we conducted a series of in vivo experiments and developed mathematical models to reveal the complex coupled heat and mass transfer processes when wearing facemasks/respirators Li et al, 2004Li et al, , 2006aLi et al, , 2006bGuo et al, 2007]. Our theoretical modeling shows that resistance to wetting is not a relatively minor issue.…”

“…On the urgent call for help from health care workers in Hong Kong, China and other parts of the world during the SARS outbreak in 2003, we felt strongly that new experiments needed to be conducted systematically to study the physical mechanisms of transmission of respiratory diseases and protection efficiency of PPE, including facemasks and respirators. Theoretical models were developed and a series of experiments were systematically designed and conducted, and were reported Li et al, 2004Li et al, , 2006aLi et al, , 2006bGuo et al, 2007]. From these studies, we raised the question whether the protection efficiency of respirator/facemask is only dependent on the filtration efficiency of filters determined by existing test standards.…”

“…Covering the filter with a fluid-resistant pre-filter, wearing a face shield or disposal after wetting are only some of the simple practical possible options, which also needs scientific evidence to guide the most effective practices. Study of the transmission pathway in terms of air fluid dynamics of the droplets [Guo et al, 2007] and coupled heat and liquid moisture transfer in filters can lead to a functional engineering design of new protective facemasks/ devices.…”