SG Shield confers protection during COVID-19 swab tests

A manikin study has shown that use of the standard face shield is not enough to protect against droplet dispersion during oropharyngeal COVID-19 swabs, but the SG Shield results in significant reduction of droplet contamination to the swab provider’s face and chest.

“Consideration should be given to adopt the design of the SG Shield to reduce contamination of the environment and provider at the source,” the researchers said.

In this study, a person wearing full personal protective equipment (PPE) whose face and chest was lined with grid paper stood in front of an airway manikin in an enclosed room. To simulate a cough, a small latex balloon containing ultraviolet fluorescent dye was set in the oral cavity of the manikin and inflated until explosion.

The researchers examined three study groups: control (no shield), face shield, and SG Shield. Droplet dispersion, the primary outcome, was determined by calculating the proportion of grip paper wall squares stained with fluorescent dye. Severity of provider contamination was the secondary outcome.

The SG Shield substantially reduced droplet dispersion to 0 percent (95 percent confidence interval [CI], 0–3.6) compared to 99.0 percent (95 percent CI, 94.6–100.0) in the controls (p=0.001). The face shield also reduced droplet contamination but to a lesser extent (80 percent, 95 percent CI, 70.8–87.3) relative to the control group (p=0.001). [Singapore Med J 2021;doi:10.11622/smedj.2021118]

Both shield groups had significantly lower qualitative severity of droplet contamination compared to the controls, but the face shield showed more contamination of the provider’s head and neck.

In addition, simulated cough intensity (as measured using peak balloon pressure) did not differ significantly between the face shield and SG Shield groups (4.5 and 4.5 per square inch [PSI], respectively) compared to the control group (4.0 PSI).

“The standard face shield is not as effective as might be assumed in protecting against contamination over the face and neck areas. An interesting observation from our study was that there was droplet contamination on the neck with the use of the face shield but not SG Shield,” the researchers said.

“The neck is an area that is often not covered by the local standard PPE, and the usual practice of changing PPE in between patients will not remove these respiratory droplets. The SG Shield thus improves protection by ensuring minimal contamination of the vulnerable neck area,” they added.

The study was limited by its small sample size, making it inadequate to detect a smaller effect size, and potential interindividual variation in cough generation and aerosol contamination, depending on external factors such as environment and wind direction. In addition, the cough was simulated by hyperinflating latex balloons until they burst at pressures of about 4 PSI.

“Although we tried to simulate the pressures of the average cough reflex around 3 PSI, these simulated coughs that were at slightly supranormal pressures were the closest we could achieve,” the researchers said. “Further research could utilize this method with a scientific particle counter to ascertain the actual number of particles that were produced and caused provider contamination.”