How Are Pathogens Transmitted?
There are a number of ways pathogens are spread and transmitted between people. Direct transmission occurs when there is physical contact between people, while indirect transmission involves contact with a non-human pathogen reservoir. Which pathogens are spread by which routes depends on the makeup and properties of the pathogens. Some common methods of transmission of bacteria, viruses and fungi include the following:
Aerosol transmission: Pathogens can be carried in small airborne particles called droplet nuclei. These particles are typically less than 5 microns in diameter and as such can be suspended in the air for several hours. When inhaled in sufficient amounts, they can cause an infection. Tuberculosis is an example of an infection transmitted by this route.
Droplet transmission: In people with infections of the upper respiratory tract, the act of sneezing and coughing expels oral or nasal droplet secretions containing the pathogens responsible for the infection. These droplets are relatively large and can stay suspended in the air for only a few minutes. The droplets can be inhaled or can enter the oral cavity via this indirect route and cause an infection. Examples of infections transmitted by the droplet route include influenza, the common cold and chicken pox.
Fomite transmission: Inanimate surfaces can become contaminated if they are touched by an infected person or if infected droplets land on them. The pathogens can then be transmitted to the hands of someone touching the surface, and then to the mouth or nose, potentially causing an infection. This is an example of indirect transmission. Pathogens can live for days to weeks on common surfaces and still cause infections when picked up by people and transferred to the body via the nose and mouth.
What Are Bloodborne Pathogens?
Bloodborne or bodily fluid transmission: The transmission of pathogens through bodily fluids such as blood is a common concern with pathogens such as HIV and hepatitis B. Transmission can occur when the infected bodily fluid from one person enters another person through cuts and abrasions, needlesticks or mucous membranes. Surfaces containing bodily fluids can also play a role in this method of transmission. Transmission of bloodborne pathogens can be either direct or indirect.
Bloodborne pathogens are infectious microorganisms that are primarily spread through contact with infected human blood and bodily fluids. They are known to cause a variety of diseases and illnesses common in humans. Some examples of bloodborne pathogens include HIV, hepatitis B virus, and hepatitis C virus.1 These types of pathogens can be encountered anywhere, including the home and workplace, but the risk of transmission is especially high in healthcare settings in which healthcare workers deal with sharp needles and other instruments that puncture the skin. Healthcare facilities and most workplaces are required to comply with the OSHA Bloodborne Pathogens Standard, which outlines protocols to protect both workers and patients from exposure and possible infection.2
What Are Foodborne Pathogens?
Foodborne pathogens are spread through contaminated food or drink, or by infected people, and can cause mild, severe and even deadly infections. Common foodborne pathogens include Salmonella enterica, Campylobacter jejuni and norovirus, but unspecified agents, or unidentified pathogens, are the largest cause of foodborne illnesses each year.
Two of the most detrimental foodborne illnesses identified by public health systems are salmonella and norovirus. Salmonella is the cause of the most deaths associated with foodborne illness in the United States annually. Norovirus is common in healthcare and long-term care settings. It can be spread through contaminated food and surfaces, and by sick people who shed the virus in their feces, contaminate their hands and then do not wash them thoroughly. While most infections are mild and resolve quickly, infections are more severe in the elderly, young children and those with pre-existing illnesses, who are less capable of effectively fighting off illness.
What Are Airborne Pathogens?
Airborne pathogens are infectious microorganisms that are commonly spread through tiny airborne particles called droplet nuclei. Typically less than 5 microns in diameter, droplet nuclei can remain suspended in the air for several hours once they are exhaled. When droplet nuclei are exhaled by someone with an infection and then inhaled by someone else, they can cause infection and disease. Tuberculosis is an example of an infectious disease that is spread through the airborne route. Viruses that infect rodents can also be spread through the airborne route, carried through tiny dust particles. Hantavirus, which is shed in the urine and feces of mice, can be carried through the air on dust particles and can cause an infection in humans if inhaled.
Pathogen Survival on Surfaces
One route of pathogen transmission is through contact with contaminated surfaces. Many pathogens can survive for long periods of time — from several hours to months — outside the human body, commonly on surfaces. For example, while the influenza virus can persist on hard, nonporous surfaces such as ceramic, plastic and steel for 8–48 hours depending on the environmental conditions,3 norovirus can persist for up to 28 days.4 In the case of norovirus, only a few virus particles can cause an infection, so the survival of even a few particles can present a transmission risk. Some bacteria such as Staphylococcus aureus can persist for up to seven months, while the spore form of Clostridium difficile can persist for up to five months.
The long survival times of common pathogens on surfaces is an issue because of the potential for transmission from surfaces to healthy people, even long after they have become contaminated. This is a concern in communal spaces such as offices, schools and athletic facilities, especially during flu season and outbreak situations, and makes effective environmental cleaning and disinfection critical to prevent the transmission of pathogens.