pH and salt content are important factors

Recognizing that aerosols are the primary transmission route for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes coronavirus disease 2019 (COVID-19), effects including: preventative measures have been introduced. Adoption of masks, air purifiers, social distancing and ventilation.

In a recent study published in Royal Society Interface Journalresearchers are analyzing how the decay of SARS-CoV-2 is affected by environmental factors such as temperature, humidity, particle and gas phase composition.

study: Differences in airborne stability of concerned SARS-CoV-2 variants are influenced by alkalinity of respiratory aerosol surrogates. Image credit: Peterschreiber.media / Shutterstock.com

About research

Vero E6 cells expressing the angiotensin-converting enzyme 2 (ACE-2) receptor and/or the transmembrane protease serine 2 (TMPRSS2) was used in the current study. His CELEBS technology, a next-generation bioaerosol technology approach, was used to assess the air stability of several SARS-CoV-2 strains, including the ancestral Wuhan strain and alpha, beta, and delta variants. it was done.

To this end, we use a droplet-on-demand dispenser to generate small droplet populations that can be resuspended in growth medium or artificial saliva. Electrodes are then applied to induce a net charge on the droplets, which are then suspended in low, medium, or high relative humidity (RH) environments of 40%, 65%, and 90%, respectively. . After the specified period, the droplets are rapidly extracted and used for cell processing within the 3-5 day culture period.

The researchers then determined the stability of SARS-CoV-2 in these droplet solutions by immunostaining for infectious virus or measuring the median tissue culture infectious dose (TCID).₅₀).

research result

SARS-CoV-2 Wuhan and Delta strains in aerosol droplets showed similar attenuation characteristics at low relative humidity. However, viability of these virus strains after long-term incubation at low relative humidity was similar to that observed at high relative humidity. When present in aerosols, both the Wuhan and Delta strains showed measurable differences in infectivity in as little as 5 minutes at different relative humidities, compared to other SARS-CoV-2 that undergo these changes over hours. Comparable to stock. This observed difference may have implications for real-world viral transmission, as infectious aerosol droplets can travel several meters in this short period of time.

The researchers then compared the air stability of different SARS-CoV-2 variants after 5 minutes of aerosolization in both low and high relative humidity. . To this end, the delta mutant had significantly reduced viral stability in the aerosol phase compared to other mutants.

After co-incubation with nitric acid, SARS-CoV-2 mutants exposed to highly acidic environments showed no change in stability in aerosol form. Notably, other studies have reported that highly acidic environments inactivate SARS-CoV-2, so aerosols may have a more basic pH that protects the virus when exposed to acidic environments. is high.

By comparison, the more basic environment significantly reduced the virus’s infectivity by up to 90% in just two minutes. This is comparable to ultraviolet (UV) radiation, which takes about 8 minutes to neutralize the virus’ infectivity.

The half-life of SARS-CoV-2 increases continuously over time, regardless of RH, suggesting that conditions within droplets become less neutralized to the virus over time. When an infected person exhales and releases infected aerosols into the surrounding environment, these aerosols become acidic over time. This may subsequently extend the half-life of SARS-CoV-2, resulting in enhanced viral transmission due to prolonged air stability.

Conclusion

After the emergence of the SARS-CoV-2 delta variant, many scientists mainly attributed the increased infectivity of this virus strain to immune-evading mutations present in the virus strain. spike protein.

However, in the current study, the researchers observed that the SARS-CoV-2 delta variant was less stable in air than the original Wuhan strain when studied at the aerosol stage. This reduced aviation stability may be an evolutionary trade-off, with the delta type exploiting a more effective route of transmission after an inhalation/deposition event.

Indoor air composition has been identified as a factor that significantly contributes to the ability of SARS-CoV-2 aerosols to remain infective. Indeed, acid vapor appears to prolong the air stability and subsequent survival of SARS-CoV-2 mutants, thereby contributing to the transmissibility of these mutants, especially in indoor environments. is.

An important implication of this study is that hypochlorous acid can unintentionally extend the time that SARS-CoV-2 remains infectious in the air, so potential SARS-CoV-2-contaminated reducing the use of bleach to disinfect sensitive areas. Nonetheless, the reaction of SARS-CoV-2 with volatile acids released from cleaning products needs further study.

In addition to careful selection of cleaning products for disinfection purposes, research findings demonstrate the importance of social distancing, mask wearing, and well-ventilated areas to minimize exposure to infectious droplets. emphasizes sexuality.