Methylene blue and light inactivates SARS-CoV-2 on N95 respirators and masks, study finds

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes the coronavirus disease 2019 (COVID-19), continues to spread worldwide. To date, there are over 73.13 million cases and 1.62 million deaths linked to COVID-19.

Throughout the pandemic, healthcare workers have grappled with overwhelming surges in severe or critical COVID-19 cases. Many countries reported a lack of supplies, including personal protective equipment (PPE) and masks.

PPEs are necessary to protect frontline healthcare personnel when they treat a COVID-19 patient. The shortages highlight the urgent need for simple, efficient, and inexpensive ways to decontaminate SARS-CoV-2-exposed PPE, ensuring the safe re-use of masks and respirators.

A new multicenter study by an international team of researchers shows that methylene blue (MB) and light can decontaminate masks and respirators by inactivating three tested coronaviruses without compromising integrity. The method is effective, low-cost, and does not require specialized equipment, making it applicable in any setting.

What is methylene blue?

Also known as methylthioninium chloride, methylene blue is a bright greenish-blue organic dye that belongs to the phenothiazine family.

Photochemical treatment is a disinfection method that uses a photosensitive drug, known as a photosensitizer. It is usually combined with visible light to produce singlet oxygen from ambient molecular oxygen in the air. The singlet oxygen inactivates viruses by damaging viral nucleic acids and membranes.

Methylene blue is a widely used photosensitizer, which has also been used to treat methemoglobinemia and in the sterilization of human plasma transfusions.

The study

The study, which appeared on pre-print medRxiv* server, aimed to determine the efficacy of methylene blue in PPE decontamination, particularly medical masks and respirators.

To determine if the method is effective, the researchers used ML and light (MBL) to inactivate coronavirus in respiratory and mask material. They tested three N95 filtering facepiece respirators (FFRs), two medical masks, and one cloth community mask.

The materials were inoculated with three types of coronaviruses, the SARS-CoV-2, murine hepatitis virus (MHV), or porcine respiratory coronavirus (PRCV). The researchers treated these materials with 10 µM MB followed by 50,000 lux of broad-spectrum light or 12,500 lux of red light for 30 minutes, or with 75°C DH for 60 minutes.

At the same time, the researchers tested respiratory and mask integrity through several standard methods. They compared the decontamination method with the FDA-approved vaporized hydrogen peroxide plus ozone (VHP+O3) decontamination method.

The study findings showed that MBL successfully and robustly inactivated all three coronaviruses with at least a 4-log reduction. Applied to FFR and medical masks, the method completely inactivated SARS-CoV-2. MBL, a novel proposed decontamination method, did not cause any changes in the breathability, filtration, and fluid resistance properties of the materials tested.

The study's findings highlight a new way for healthcare workers to re-use masks, respirators, and PPEs safely. The method can also be used to supply active viral inactivation while wearing the PPEs. As a result, this may solve the shortage of PPEs, which are considered vital to protect healthcare workers from being infected.

We provide the first evidence that methylene blue and light can inactivate human coronavirus on FFRs and MMs commonly worn by healthcare personnel and essential workers without decreasing performance and fit,” the researchers concluded.

“Our findings provide a recipe for easily accessible, inexpensive, effective PPE re-use and afford an opportunity for utilization in high- and low-resource settings to address issues of global supply shortages and reduced time of decontamination relative to VHP+03,” they added.

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
Angela Betsaida B. Laguipo

Written by

Angela Betsaida B. Laguipo

Angela is a nurse by profession and a writer by heart. She graduated with honors (Cum Laude) for her Bachelor of Nursing degree at the University of Baguio, Philippines. She is currently completing her Master's Degree where she specialized in Maternal and Child Nursing and worked as a clinical instructor and educator in the School of Nursing at the University of Baguio.


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