The coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) agent, has infected more than 63.93 million people and has claimed the lives of over 1.49 million worldwide.
The virus primarily spreads through respiratory droplets or aerosols that stay suspended in the air when an infected person coughs, sneezes, speaks or breathes. In some cases, these droplets remain on commonly touched surfaces (or fomites), such as tables, doorknobs, telephones, and elevator buttons.
A new study, published in the journal Science of the Total Environment, found that particulate matter (PM) plays a role in providing surfaces for pathogen transmission and interaction, enabling fomite transmission through deposition. Further, PM contributes to the chronic weakening of the immune and respiratory system, making the virus more potent in countries with higher PM levels.
Study background
The current pandemic has resulted in an unprecedented healthcare burden and major economic ramifications across the globe.
Many studies have tackled the SARS-CoV-2, how it spreads, and potential therapeutic targets. However, the virus's survival and transmission from an infected person through the air and water-borne channels, including its interactions with surfaces, environmental factors, and chemicals, remain unclear.
Particulate matter (PM) is the sum of all solid and liquid particles suspended in the air. Many of these particles, including dust, pollen, soot, smoke, and liquid droplets, are hazardous.
The researchers aim to determine PM's role in the transmission of SARS-CoV-2, determine gaps in the field, and provide a better understanding of transmission and survival of the novel coronavirus.
The study
The researchers, who were from the CSIR-National Environmental Engineering Research Institute (NEERI) in India, looked into relevant studies on the factors of transmission and survival of SARS-CoV-2. The studies included meteorology, air pollution, aerosol droplet size, wastewater contact, inanimate surfaces, and other chemicals.
Further, the team also studied the chemical composition of these factors, which can significantly affect SARS-CoV-2 survival and transmission.
Lastly, the study highlights potential air and water-borne routes, suggesting the need for further studies on the effects of particulate matter characteristics on the novel coronavirus. It is essential to understand the link between particulate matter (PM) and SARS-CoV-2 since PM is predominantly found in ambient spaces and surfaces.
The researchers noted the survival and transmission of SARS-CoV-2. They said that hospitals and quarantine facilities are high-risk environments for nosocomial transmission. Due to the risk, extra disinfection and preventive measures are needed to reduce cross-infection.
In the community, transmission can often occur through close contact with infected family members or in crowded public places. When the SARS-CoV-2 virus particle is inhaled, the virus's Spike protein binds with the angiotensin-converting enzyme 2 (ACE2), the cellular gateway for the virus to enter and infiltrate the cell. ACE2 receptors are highly expressed in many parts of the body, including the respiratory tract, lungs, intestines, kidneys, and heart.
SARS-CoV-2 modes of transmission
SARS-CoV-2 can spread through droplet transmission. Exhalation via sneezing or coughing from an infected person produces respiratory droplets and droplet nuclei, that can travel up to one meter in distance. On the other hand, airborne particles can travel even up to tens of meters in the air.
Also, respiratory droplets can evaporate and transform into droplet nuclei. When the virus becomes airborne, the aerosols can interact with several air components, which can affect its survival.
If the aerosols come in contact with a toxic component in the atmosphere, it may become inactivated and can no longer transmit the disease. The half-lives of SARS-CoV-2 in aerosols are believed to be about 1.1 to 1.2 hours.
SARS-CoV-2 can also spread via contact or fomite transmission. The respiratory droplets exhaled from an infected person settle down on nearby fomites. They can be on surfaces such as tables, the floor, doorknobs, and other commonly touched areas. People can come in contact with the respiratory droplets by touching contaminated surfaces and then touching their mouth, nose, or eyes.
Fomite transmission would depend on the surface characteristics, affecting virus survival and determining the extent of the infection's spread.
Fecal transmission is also a potential mode of infection. In a past study, it was found that SARS-CoV-2 is stable in feces at room temperature for a minimum of one to two days and can survive for up to four days in the stool of patients with diarrhea.
Particulate matter and COVID-19
Upon reviewing several studies, the researchers found that SARS-CoV-2's airborne transmission is one of its most potent forms of infection. The studies showed that virus-laden droplets' interactions could potentially infect a person in direct contact, but these can be airborne and can travel long distances.
Moreover, ultrafine particles found in ambient air have residence times of days to weeks, enabling the transport of up to thousands of kilometers in the atmosphere. Meanwhile, coarser and bigger particles tend to deposit quicker.
The researchers also found that airborne virus-laden droplet nuclei can interact with particulate matter by getting absorbed on the particulate surfaces.
The researchers believe that further studies about particulate matter and viruses are needed to understand PM composition's impact on virus survival.
The team concluded that PM plays a vital role as a surface for pathogen transmission. It facilitates fomite transmission, and at the same time, it can weaken the immune and respiratory systems, which are the common targets of SARS-CoV-2 infection.
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