Infectious respiratory particles are droplets or aerosols released into the air when an infected person breathes, talks, coughs, or sneezes. These particles can carry contagious agents such as viruses and bacteria, capable of transmitting respiratory diseases to others. Read here to learn more.
Understanding the characteristics and behaviour of these particles is critical for controlling the spread of respiratory infections, including common illnesses like the flu and the common cold, as well as more severe diseases such as tuberculosis, COVID-19, and measles.
Transmission of pathogens through the air
Following consultation with public health agencies and experts, the World Health Organization (WHO) published a global technical consultation report introducing updated terminology for pathogens that are transmitted through the air.
The extensive consultation resulted in the introduction of the following common descriptors to characterize the transmission of pathogens through the air (under typical circumstances):
- Individuals infected with a respiratory pathogen can generate and expel infectious particles containing the pathogen, through their mouth or nose by breathing, talking, singing, spitting, coughing or sneezing.
- These particles should be described with the term ‘infectious respiratory particles or IRPs.
- IRPs exist on a continuous spectrum of sizes, and no single cut-off points should be applied to distinguish smaller from larger particles.
- This facilitates moving away from the dichotomy of previously used terms: ‘aerosols’ (generally smaller particles) and ‘droplets’ (generally larger particles).
The descriptor ‘through the air’ can be used in a general way to characterize an infectious disease where the main mode of transmission involves the pathogen travelling through the air or being suspended in the air.
Under the umbrella of ‘through the air transmission’, two descriptors can be used:
- Airborne transmission or inhalation, for cases when IRPs are expelled into the air and inhaled by another person.
- Airborne transmission or inhalation can occur at a short or long distance from the infectious person and distance depends on various factors (airflow, humidity, temperature, ventilation etc).
- IRPs can theoretically enter the body at any point along the human respiratory tract, but preferred sites of entry may be pathogen-specific.
- Direct deposition, for cases when IRPs are expelled into the air from an infectious person, and are then directly deposited on the exposed mouth, nose or eyes of another person nearby, then entering the human respiratory system and potentially causing infection.
Characteristics of Infectious Respiratory Particles
- Size: Respiratory particles vary widely in size, generally categorized into:
- Large Droplets: Typically larger than 5 micrometres in diameter. These droplets are heavy enough to quickly fall to the ground or surfaces within seconds to minutes, typically within a range of up to 6 feet (about 2 meters) from the source.
- Aerosols (Droplet Nuclei): These are smaller particles, usually less than 5 micrometres in diameter. Due to their small size, aerosols can remain suspended in the air for hours and travel long distances with airflow.
- Composition: The particles consist of saliva or respiratory secretions, and can contain a variety of pathogens depending on the illness of the carrier.
- Infectivity: The ability of these particles to cause infection depends on factors such as the type and amount of pathogen they carry, the susceptibility of the person exposed to them, and environmental conditions (e.g., humidity, temperature).
Transmission:
- Direct Transmission: This occurs when respiratory droplets from an infected person directly reach the mucous membranes (eyes, nose, mouth) of a nearby person. This is common during close contact.
- Airborne Transmission: Involves the inhalation of aerosols containing infectious agents, which can occur over longer distances and times than droplet transmission.
- Fomite Transmission: Although not as common as direct respiratory transmission, infectious particles can settle on surfaces where they can survive for varying periods. Other individuals can acquire the pathogens by touching these contaminated surfaces and then touching their face.
Control Measures
- Ventilation: Improving indoor ventilation can reduce the concentration of airborne particles, thereby reducing the risk of airborne transmission.
- Masks and Respirators: Wearing masks or respirators can significantly reduce the emission and inhalation of infectious particles.
- Physical Distancing: Maintaining distance from others reduces the risk of direct droplet transmission.
- Hand Hygiene: Regularly washing hands can minimize the risk of touching surfaces contaminated with infectious particles.
- Surface Cleaning and Disinfection: Regularly disinfecting surfaces in high-touch areas helps reduce fomite transmission.
Why in the news?
Pathogens that transmit through the air will be described by the term ’infectious respiratory particles’ or IRPs, according to the World Health Organization (WHO).
- The world health body has thus ended the lack of a common terminology to describe the transmission of these pathogens, which was particularly challenging during the global COVID-19 pandemic.
- The pathogens covered include those that cause respiratory infections, e.g. COVID-19, influenza, measles, Middle East respiratory syndrome (MERS), severe acute respiratory syndrome (SARS), and tuberculosis, among others.
- The announcement came following wide-ranging consultations across multiple steps in 2021-2023.
- The publication, entitled “Global Technical Consultation Report on proposed terminology for pathogens that transmit through the air”, is the result of an extensive, multi-year, collaborative effort and reflects shared agreement on terminology between WHO, experts and four major public health agencies: Africa Centres for Disease Control and Prevention; Chinese Center for Disease Control and Prevention; European Centre for Disease Prevention and Control; and United States Centers for Disease Control and Prevention.
- This agreement underlines the collective commitment of public health agencies to move forward together on this matter.
Conclusion
Understanding the dynamics of infectious respiratory particles is crucial in managing outbreaks of respiratory diseases.
Public health policies, especially in the context of pandemics like COVID-19, heavily rely on insights about particle behaviour to formulate guidelines on mask usage, social distancing, and other preventive measures.
Effective management of these particles through engineering controls (like ventilation), administrative controls (like occupancy limits), and personal protective equipment is vital in preventing the spread of infections in community settings.
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-Article by Swathi Satish
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