Most respiratory viruses are spread by aerosols

Respiratory viruses, including COVID-19, are widely believed to be spread primarily through droplets produced when an infected person coughs and sneezes or through contact with contaminated surfaces. However, this review argues that this conventional wisdom may be wrong. Researchers have found that aerosols are the most likely primary route of transmission for most respiratory diseases by studying superspreading events during the new crown epidemic, as well as the transmission of many other types of respiratory diseases.

Respiratory aerosols are formed by exhalation activities such as breathing, talking, singing, shouting, coughing and sneezing, the researchers noted. The size of aerosols largely determines how long they can stay suspended in the air, how far they can reach, whether they can be inhaled, and if inhaled, how deeply they can enter the respiratory tract.

The study found that most of the aerosols produced by respiratory activity are smaller than 5 microns in size, which allows them to penetrate deep into and deposit in the bronchiolar and alveolar regions. The study also found that the virus is more enriched in aerosols below 5 microns. The researchers found that more than half of the viral RNA was in aerosols no larger than 4-5 microns in samples collected from flu patients when they breathed, talked and coughed. In a study of influenza viruses, more than half of the influenza A virus RNA was found in aerosols no larger than 2.5 microns.

In addition, the researchers note that another unique behavior of aerosols that should be seriously considered is that their ability to spread is affected by airflow and ventilation. Ensuring adequate ventilation rates, filtration, and avoiding recirculation can help reduce airborne transmission of viruses from infectious aerosols.

A carbon dioxide detector helps verify adequate ventilation. Installing portable high-efficiency particulate air purifiers, or installing UV disinfection systems in upstairs rooms can also help reduce the concentration of virus-carrying aerosols. COVID-19 vividly illustrates the importance of long-underestimated airborne routes and the need to protect people from breathing clean and pathogen-free air.

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