Which facemasks work best at stopping coronavirus?

By Dr. Ananya Mandal, MDJul 1 2020

A new study shows how wearing masks can prevent the spread of droplet borne infections and is an excellent preventive measure to stop the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. The study titled, "Visualizing the effectiveness of face masks in obstructing respiratory jets," is published in the latest issue of the journal Physics of Fluids.

The smallest respiratory droplets leak through a face mask constructed using a folded handkerchief. Despite the leakage, the spread of the droplets is impeded considerably compared to no mask use. Image Credit: Siddhartha Verma, Manhar R. Dhanak and John Frankenfield

The COVID-19 pandemic and its spread

The novel coronavirus made its first appearance late December 2019 in Wuhan, China, and it was on the 30^th of January that it was declared a global emergency by the World Health Organization (WHO). Owing to the rapid spread from person to person via droplets, the infection spread rapidly across the world and was finally declared a pandemic on the 11^th of March 2020.

As of today, 10,662,993 persons have been infected across the world, and it has killed 515,504 individuals, according to the Center for Systems Science and Engineering (CSSE) at Johns Hopkins University (JHU).

According to the health organization, the virus mostly spreads from an infected person to another when they cough or sneeze and the virus is released in droplets released from the mouth and nose. To break the chain of transmission, it has been recommended that all individuals wear face masks.

What was this study about?

The researchers explain that "there are no specific guidelines on mask materials and designs that are most effective in minimizing droplet dispersal." There are several types of masks available, including "cloth-based coverings" to "medical-grade masks" they write. The former is widely distributed to the public.

The team explains that around 35 percent of the COVID-19 cases are unaware of their infection because of no symptoms. These individuals are capable of spreading the infection to others via respiratory droplets if they move around with their faces uncovered and are within range of other non-infected persons.

Not just COVID-19, these respiratory droplets are also capable of spreading other viral and bacterial infections such as "common cold, influenza, tuberculosis, SARS (Severe Acute Respiratory Syndrome), and MERS (Middle East Respiratory Syndrome)," wrote the researchers.

What was done?

For this study, the team used "qualitative visualizations" of simulated coughs and sneezes and looked at the impact of the different types of masks on the extent of droplet filled respiratory secretions.

For simulating the cough, they used a mannequin's head attached to a fog machine. The fog machine is capable of creating a vapor from glycerine and water. A pump was used to expel the vapor from the nose and mouth of the mannequin. These vapor droplets were visualized using a laser sheet by passing green laser pointer rays through a cylindrical rod. The team photographed the green vapors coming out of the mouth of the mannequin wearing the different types of masks.

The comparisons of the average jet distance of these coughed or sneezed were checked when the simulators wore no masks, bandanas made of elastic t-shirt material, folded handkerchiefs made of cotton, stitched masks made of quilted cotton and commercial masks of unknown material. The threads per inches in the masks tested were 85 in bandanas, 55 in folded handkerchiefs, 70 in stitched masks, and randomly assorted fibers in commercial masks.

Lead study researcher Siddhartha Verma, an assistant professor at Florida Atlantic University's College of Engineering and Computer Science, in his statement, said, "The visuals used in our study can help convey to the general public the rationale behind social-distancing guidelines and recommendations for using face masks."

Speaking about how they devised a method to simulate the coughs and sneezes, he said, "The main challenge is to represent a cough and sneeze faithfully. The setup we have used a simplified cough, which, in reality, is complex and dynamic."

What was found?

Results showed that folded loose masks and bandana coverings over the face could provide minimal protection and had the least ability to stop the respiratory droplets containing the virus.

The team wrote, "Well-fitted homemade masks with multiple layers of quilting fabric, and off-the-shelf cone style masks proved to be the most effective in reducing droplet dispersal."

The average distance jets of aerosols were propelled were as follows;

• Without face-covering – around 8 feet
• With bandana like covering – 3 feet 7 inches
• With folded handkerchiefs – 1 foot 3 inches
• With stitched well-fitted masks – 2.5 inches
• With commercial fitted cone-shaped masks – 8 inches

The authors wrote that the well-fitted masks and the commercial masks reduced both speed and range of the reparatory droplets. There was, however, risk of leakages through the material of the mask from the gaps along the edges they wrote.

Implications

The team emphasizes that current guidelines of social distancing to prevent the spread of the COVID-19 infection is 6 feet, and it is seen that uncovered faces can allow the jet propulsions for up to 8 feet. They wrote, "uncovered emulated coughs were able to travel notably farther than the currently recommended 6-ft distancing guideline".

The researchers have outlined the procedure for conducting similar emulation and visualization studies to check the effectiveness of various face covers in the spread of droplet borne infections. They add that readily available materials could be effective, and their study can help medical researchers, health care professionals, and manufacturers to assess the qualitative efficacy of the personal protective equipment.

Verma said, "Promoting widespread awareness of effective preventive measures [for COVID-19] is crucial at this time as we are observing significant spikes in cases of COVID-19 infections in many states, especially Florida." He added, "It is also important to understand that face coverings are not 100% effective in blocking respiratory pathogens. This is why it is imperative that we use a combination of social distancing, face coverings, hand-washing, and other recommendations from health care officials until an effective vaccine is released."

Silk study

This research ties in with another recent study by a team at the University of Cincinnati that looked to determine what fabrics were the most effective for facemasks. The team examined the hydrophobicity of fabrics (silk, cotton, polyester), as measured by their resistance to the penetration of small and aerosolized water droplets, an important transmission avenue for the virus causing COVID-19.  

The researchers found that when used for protection of the face, silk was the most effective at preventing the penetration of droplets, and the least absorptive of water, because of its intensely hydrophobic character compared to the other fabrics tested. This research is published on the preprint server medRxiv*, prior to peer review.