Respiratory route of transmission
The respiratory route of transmission refers to the process through which pathogens, such as bacteria and viruses, are spread via airborne droplets expelled by an infected individual. These droplets can be released during actions like coughing, sneezing, talking, or even laughing, allowing pathogens to be inhaled by others nearby or to land on their mucous membranes. Common diseases transmitted this way include bacterial infections like strep throat and tuberculosis, as well as viral illnesses such as the common cold, influenza, and measles. The droplets are relatively large and do not linger in the air for extended periods; instead, they settle on surfaces within a short time, maintaining pathogen viability for several hours.
Given the contagious nature of respiratory infections, public health measures, such as maintaining physical distance and practicing respiratory hygiene, are essential to reduce transmission risk. The impact of respiratory transmission gained heightened awareness during outbreaks, such as SARS and the H1N1 influenza pandemic, highlighting the importance of preventive practices like vaccination and proper hygiene. To combat these infections, individuals are encouraged to use tissues when sneezing or coughing, wear masks when necessary, and practice thorough hand hygiene. Understanding these dynamics is crucial for managing public health and preventing the spread of respiratory diseases.
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Respiratory route of transmission
- ALSO KNOWN AS: Aerosol transmission, droplet contact, droplet transmission
Definition
In the respiratory route of transmission, a sick person who coughs or sneezes emits airborne droplets of respiratory secretions that contain pathogens (bacteria or viruses). These droplets may be breathed in by another person, who can then become infected. In addition, droplets that land on another person’s face may be absorbed through the mucous membranes of the eyes, nose, and mouth, thus infecting that person. Droplets may also be expelled when a person talks, sings, laughs, or vomits. Droplets containing pathogens and respiratory mucus are too large to remain in the air for long and quickly settle on nearby surfaces, where the pathogens can survive up to three hours.
Bacterial diseases commonly transmitted by droplet transmission are bacterial meningitis, strep throat, tuberculosis, and whooping cough (pertussis). Viral diseases transmitted by droplet transmission include the common cold, influenza, mumps, measles, rubella (German measles), and chickenpox. These pathogens thrive in the warm, moist environment of the upper respiratory tract. Some viruses can replicate only in respiratory epithelial cells.
An upper respiratory infection is highly contagious. As many as three thousand droplets can be expelled in a single cough. This could result in the release of as many as twenty thousand viruses. A sneeze releases droplets at a speed of 373 miles (600 kilometers) per second. In cases of influenza, a person can infect others beginning one full day before the onset of symptoms and up to one week after symptoms appear. In cases of measles, 90 percent of unvaccinated or immunocompromised persons living with an infected person will become infected. Human rhinovirus, which causes the common cold, is the most common infective virus, perhaps because of its minimal size; less common infective viruses are ten times larger.
Respiratory Hygiene
“Respiratory hygiene” is a term coined by the Centers for Disease Control and Prevention to describe measures that can be taken to decrease the risk of spreading respiratory pathogens. A minimum of three feet of space should be maintained between an infected person and others. When it is necessary to work within three feet of another person, the infected person should wear a disposable medical-procedure mask.
Persons not wearing a mask should cough or sneeze into tissues, dispose of the tissues promptly, and wash their hands with antiseptic soap or an alcohol-based hand sanitizer. Hands should be washed with soap for a minimum of fifteen seconds in warm water and then dried with a disposable towel or a heated blower. Hand sanitizer should not be used on hands that are visibly soiled because it may not reach all pathogens effectively. Tissues and paper towels should be discarded in a no-touch receptacle.
If tissues are not available, one should cough or sneeze into his or her sleeve or elbow. An August 2009 observational study by medical students at Otago University in Wellington, New Zealand, found that 1 in 77 people covered sneezes and coughs with the arm, while 1 in 30 people used a tissue or handkerchief. Most of the people observed sneezing and coughing in public still covered their mouth with their hands. However, 1 in 4 people failed to cover their cough or sneeze with anything.
Impact
The respiratory route of transmission was brought to increased public attention in 2003 with the outbreak of severe acute respiratory syndrome (SARS), which is caused by a previously unknown coronavirus, and again in 2009 with the pandemic caused by the influenza A (H1N1) virus. News reports showed people wearing disposable medical masks in schools and businesses and when using public transportation. The mortality rate of nearly 10 percent and the more than twelve thousand flu-related deaths in the United States alone prompted funding for research into the respiratory transmission of diseases, particularly the transmission of viruses. Respiratory transmission is a primary method of transmission for COVID-19, which caused the COVID-19 pandemic in the early 2020s that resulted in millions of deaths across the world.
The use of alcohol-based hand sanitizers has become more common, and people are learning to cover their coughs and sneezes with something other than their hands. Annual flu vaccines are becoming more popular. Nasal sprays of live attenuated virus are alternatives to vaccines of killed virus. Treatment with the antiviral drugs Tamiflu (oseltamivir) or Relenza (zanamivir) is recommended for people with influenza who require hospitalization.
Bibliography
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Cao, Bin, et al. “Clinical Features of the Initial Cases of 2009 Pandemic Influenza A (H1N1) Virus Infection in China.” New England Journal of Medicine 361 (2009): 2507-2517.
Gralton, Jan, et al. “The Role of Particle Size in Aerosolised Pathogen Transmission: A Review.” Journal of Infection 62 (2011): 1-13.
"Number of COVID-19 Deaths Reported to WHO." Worth Health Organization, 2025, data.who.int/dashboards/covid19/deaths. Accessed 4 Feb. 2025.
Wald, Priscilla. Contagious: Cultures, Carriers, and the Outbreak Narrative. Durham, N.C.: Duke University Press, 2007.