April 8, 2021

Methods of Pathogen Transmission to Consider

Methods of Pathogen Transmission to Consider

Per the CDC, The principal mode by which people are infected with SARS-CoV-2 (the virus that causes COVID-19) is through exposure to respiratory droplets carrying infectious virus. Respiratory droplets are produced during exhalation (e.g., breathing, speaking, singing, coughing, sneezing) and span a wide spectrum of sizes that may be divided into two basic categories based on how long they can remain suspended in the air:

  • Larger droplets, some of which are visible, that fall out of the air rapidly within seconds to minutes while close to the source.
  • Smaller droplets and particles (formed when small droplets dry very quickly in the airstream) that can remain suspended for many minutes to hours and travel far from the source on air currents.

Once respiratory droplets are exhaled, and as they move outward from the source their concentration decreases and is diluted by the growing volume of air they encounter.

Respiratory viruses are transmitted in multiple ways.

Infections with respiratory viruses are principally transmitted through three modes: contact, droplet, and airborne.

  • Droplet transmission is infection spread through exposure to virus-containing respiratory droplets (i.e., larger and smaller droplets and particles) exhaled by an infectious person. Transmission is most likely to occur when someone is close to the infectious person, generally within about 6 feet.
  • Contact transmission is infection spread through direct contact with an infectious person (e.g., touching during a handshake) or with an article or surface that has become contaminated. The latter is sometimes referred to as “fomite transmission.”
  • Airborne transmission is infection spread through exposure to those virus-containing respiratory droplets comprised of smaller droplets and particles that can remain suspended in the air over long distances (usually greater than 6 feet) and time (typically hours).  

Is COVID Airborne?

Per CDC and BioMed Central, yes. Aerosols are liquid particles dispersed in the air and contain particles, like microorganisms or industrial particles. It is hypothesized that when an infected person with SARS-CoV-2 breathes heavily, sneezes, or coughs, the SARS-CoV-2 will be excreted and make bio-aerosols. As mentioned above, bio-aerosols < 5 μm in diameter causes airborne transmission; however, larger ones that land on a surface might cause contact transmission. 

According to Hackensack Meridian Health, Aerosols may move through the air within an enclosed space, infecting people who are farther away than six feet. They may also hang in the air after someone with COVID-19 has moved on, infecting others who breathe the tiny particles in. The more time that you spend in a poorly ventilated indoor space and the more crowded it is, the greater your risk is of contracting COVID-19. 

For these reasons, experts recommend against spending extended periods in indoor spaces with other people, especially if you aren’t wearing a mask. Face masks were used for decades as a  preventative tool against  viral infections, and continue to be a person’s first line of defense when exposed to potentially infectious air.

Risk for Fomite (Surface) Transmission

Per the CDC, Fomite transmission varies by location (comparing child daycares, schools, offices, and nursing homes), disinfection strategy, and surface type. Although precise values likely vary on a case-by-case basis, child daycares are assumed to have higher frequency of fomite touching and the fraction of surfaces susceptible to contamination than offices, whereas schools are likely intermediate for both factors. Nursing homes are assumed to have similar amounts of surfaces susceptible to contamination to offices, but higher fomite touching rates.

Combining surface cleaning and decontamination with mask wearing can help mitigate this risk. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease, can be transmitted through close contact. However, the virus also persists for up to 28 days on surfaces suggesting that surface-mediated transmission might also occur. Infectious persons shed pathogens onto fomites or hands, but only a fraction of surfaces are accessible for contamination. Hands might become contaminated from viral excretion or from touching virus-contaminated fomites. Susceptible persons might become infected through touching their face and mouth with contaminated hands.


Per the NHS, There are 3 main ways that germs are spread by clothes and towels:

  • When towels or bedlinen are used by more than 1 person germs can spread between them.
  • When someone handles dirty laundry they can spread germs onto their hands.
  • When clothes are washed, germs can spread between items in the process of being washed.

Germs on clothes and towels can come from our own body or from being in close contact with an ill person. This might include caring for a sick family member, or accidentally brushing up against a sick stranger. Germs can also get onto outer clothing if you handle contaminated food or brush against a soiled object.

Hackensack Meridian Health suggests that COVID-19 doesn’t survive for long on clothing, compared to hard surfaces, and exposing the virus to heat may shorten its life. A study published found that at room temperature, COVID-19 was detectable on fabric for up to two days, compared to seven days for plastic and metal. However, when it was exposed to high heat, the virus became inactive within five minutes.

Another study by De Montfort University, revealed  how coronavirus behaves on three fabrics commonly used in the healthcare industry, researchers found that traces can remain infectious for up to three days. The results showed that polyester poses the highest risk for transmission of the virus, with infectious virus still present after three days that could transfer to other surfaces. On 100% cotton, the virus lasted for 24 hours, while on polycotton, the virus only survived for six hours.


Health Line states that shoes tend to be a lot dirtier than clothing just by their very nature. As such, they’re more likely to carry bacteria and other contaminants into the home. A recent interview with Kevin W. Garey, PharmD, MS, FASHP, Professor and Chair of the Department of Pharmacy Practice and Translational Research at University of Houston College of Pharmacy, discusses the threat of shoe-borne pathogens and how quickly they can spread to the entire hospital. For example, with the hospital pharmacy being the hub for the entire facility, an individual transporting medicines also carrying coronavirus can quickly spread the virus throughout the hospital. 

Per Healthcare Facilities Today,  Often, organisms are spread by us stepping on them and moving them around as we walk. That’s why maintaining the  floors as best as possible is so crucial to infection prevention and control. Because of the square footage of the floor and how highly trafficked it is, you can’t clean it frequently enough, which is often what leads the floor to become a hotbed for pathogen transmission.