Disease Transmission

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Disease Transmission Objectives

List examples of human-to-human, vector, and environmental infectious disease transmission.
Provide examples of diseases and their forms of transmission, including viral Hepatitis and COVID-19.
Explain how food-borne infectious disease transmission can be reduced, and provide examples of safe food preparation and storage.

A key to addressing infectious diseases is to adequately understand transmission.

Many day-to-day activities, like washing hands and cooking food, are intended in part to reduce disease transmission.

Infectious disease transmission can be broken into three categories.

Human to Human

This includes respiratory transmission, skin contact, sexual contact, and mother to baby.

Vector

An animal like a mosquito or tick transmits pathogens to a human.

Environmental

A pathogen is acquired from the environment by drinking contaminated water, eating contaminated food, or through soil.

There are numerous ways an infectious disease agent can be transmitted to a human. Some of these are more obvious, others have more obscure names. Iatrogenic transmission means through a medical procedure like using a needle or a blood product. Vertical transmission refers to a mother transmitting to a baby immediately before or after birth.

Human-to-human sexual transmission can be reduced with use of prophylactics, measures that prevent disease.

Some diseases can result from multiple forms of transmission like viral hepatitis A, B, and C.

Environmental transmission includes contaminated drinking water and food. This video shows some of the common water-borne and food-borne pathogens that cause infections.

This poster provides a structure for thinking about food-borne pathogens.

We know we are supposed to heat and/or cool certain foods, but the temperatures required may be a surprise.

An additional, and potentially important, food safety step is added in this video.

There are additional photos of food safety recommendations on this guide’s resource page.

Resources

SARS-CoV-2 Transmission

We have received many excellent questions about COVID-19 and the virus SARS-CoV-2. Several of these questions and answers are located throughout this module, matched with each topic.

Q. If I someone is unvaccinated or immunocompromised, do they need to wear a mask if 6 feet away from people?

A. Short answer is possibly. There are multiple factors at play here. First, research indicates that this virus spreads further than six feet away from its host. This is a small virus that can remain airborne for a period of time. Variables include location (indoors vs. outdoors), air currents, dispersal force (breathing, talking, sneezing), and the time spent within the range of an infected individual. Additional variables may be the type of mask, the fit of the mask, and mask handling. Also, research on use of masks indicates that masks are not 100% effective in stopping infection, some health care workers became infected wearing fitted quality masks. However masks do drop infection rate significantly. Also at play is the health of the individual in how significant an infection can become. This is a case where consulting a health care professional familiar with an individual’s medical situation can be advantageous.

Q. If the primary form of covid transmission is respiratory why did we wash everything?

A. This is a good question, and it has to do with the time it takes to learn about a new pathogen and concerns about reducing the percentage of risk in the mean time. Staying a distance away from other people reduces risk for transmission of many infectious diseases, wearing a mask reduces risk even more. Not touching the eyes, nose, or mouth, reduces risk. Washing hands after touching an object that may have a virus on it may have shaved off even more risk potential. Think of it as a game, and you want the risk of exposure to drop from 100% to as close to 0% as possible without a significant drop in quality of life. One behavior may not be adequate, the risk remains too high. Combining multiple behaviors drops the risk lower and lower. Practicing all of the risk-reducing behaviors all the time has you prepared for changing circumstances. Although research now supports that covid-19 is primarily spread through respiratory transmission, reduction of the spread of other pathogens like influenza and rhinoviruses reduces occurrence of other impactful diseases.

Some people will continue to wear masks for many reasons, including compromised immune systems, concerns over risks for other infectious diseases or airborne allergens, or simply supporting immunocompromised friends and family.

The next section introduces the first large-scale infectious disease eliminated by human effort: Smallpox.

Check your knowledge. Can you:

list examples of human-to-human, vector, and environmental infectious disease transmission?
provide examples of diseases and their forms of transmission, including viral Hepatitis and COVID-19?
explain how food-borne infectious disease transmission can be reduced, and provide examples of safe food preparation and storage?

Go back to the Eliminating Infectious Diseases Guide Overview

Go forward to the Smallpox Page

Eliminating Infectious Diseases Lecture Guide Contents

The material from this guide and corresponding lecture is assessed on the weekly quiz.