Ozone May Effectively Disinfect PPE for Reuse

Dentistry Today


Ozone gas, a highly reactive chemical comprising three oxygen atoms, could provide a safe means for disinfecting certain types of personal protective equipment (PPE) that are in high demand for shielding healthcare personnel from COVID-19, according to the Georgia Institute of Technology.

Using two pathogens similar to the novel coronavirus, the study found that ozone can inactivate viruses on items such as Tyvek gowns, polycarbonate face shields, goggles, and respirator masks without damaging them, as long as they don’t included stapled-on elastic straps. The consistency and effectiveness of the ozone treatment depended on maintaining relative humidity of at least 50% in chambers used for disinfection.

“Ozone is one of the friendliest and cleanest ways of deactivating viruses and killing most any pathogen,” said MG Finn, PhD, chair of Georgia Tech’s School of Chemistry and Biochemistry, who led the study. “It does no leave a residue, it’s easy to generate from atmospheric air, and it’s easy to use from an equipment perspective.”

Ozone can be produced with inexpensive equipment by exposing oxygen in the atmosphere to ultraviolet light or through an electrical discharge such as a spark.

During local and regional peaks in coronavirus infection, PPE shortages can force healthcare facilities to reuse PPE intended for single use. Healthcare facilities have used ultraviolet light, vaporized hydrogen peroxide, heat, alcohol, and other technique to disinfect these items, but until recently, there had not been much interest in ozone disinfection for PPE, said Finn, who also holds the James A. Carlos Family Chair for Pediatric Technology.

Ozone is widely used for disinfecting wastewater, purifying drinking water, sanitizing food items, and disinfecting certain types of equipment, including clothing. Ozone disinfection cabinets are commercially available, taking advantage of the oxidizing effects of the gas to kill bacteria and inactivate viruses.

“There was no reason to think it wouldn’t work, but we could find no examples of testing done on a variety of personal protective equipment,” said Finn. “We wanted to contribute to meeting the needs of hospitals and other healthcare organizations to show that this technique could work against pathogens similar to the coronavirus.”

Virologist Phil Santangelo, PhD, of the Wallace H. Coulter Department of Biomedical Engineering recommended two respiratory viruses, influenza A and respiratory syncytial virus (RSV), as surrogates for coronavirus. The two are known as “enveloped” viruses because, like coronavirus, they are surrounded by a lipid outer membrane. They also are less dangerous than SARS-CoV-2, allowing the researchers to study them without high-containment lab facilities.

The researchers devised a test procedure in which solutions including the two viruses were placed onto samples of the PPE items under study. The solutions were allowed to dry before the samples were placed in a chamber into which ozone was introduced at varying concentrations as low as 20 parts per million.

After treatment for different lengths of time, the researchers tested the PPE samples to determine whether or not any of the viruses on the treated surfaces could infect cells grown in the laboratory. The entire test procedure required about a day and a half.

“The protocol we set up reports very sensitively on whether or not the virus could reproduce, and we found that the ozone was very successful in rendering them harmless,” said Finn. “Oxidizing biological samples to a significant extent is enough to inactivate a virus. Either the genetic material or the outer shell of the virus would be damaged enough that it could no longer infect a host cell.”

Loren Williams, PhD, a professor with the School of Chemistry and Biochemistry, introduced the researchers to a manufacturer of ozone disinfection chambers, which allowed evaluation of the equipment using the test protocol. During the test, the researchers learned that having sufficient relative humidity in the chamber of at least 50% was essential for rapidly inactivating the viruses in a consistent manner.

After subjecting face masks and respirators to ozone disinfection, the researchers worked with associate professor Nga Lee (Sally) Ng, PhD, of the School of Chemical and Biomolecular Engineering to evaluate the filtration capabilities of the items. The ozone treatment didn’t appear to negatively affect the N95 filtration material.

While the ozone didn’t harm the filtration ability of the masks, it did damage the elastic materials used to hold the masks on. While the elastic headbands could be removed from the masks during ozone disinfection, removing and replacing them on a large scale may make the ozone treatment technique impractical. Otherwise, however, ozone may offer an alternative technique for disinfecting other types of PPE.

“Ozone would be a viable method for hospitals and other organizations to disinfect garments, goggles, and gloves,” said Finn. “It is inexpensive to produce, and we hope that by sharing information about what we’ve found, healthcare facilities will be able to consider it as an option, particularly in low-resource areas of the world.”

The researchers have posted the study on the medRxiv preprint server.

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