Modes of Transmission: How Bacteria are Spread and Why They are Infectious
There are a few different ways that bacteria can spread. These are known as modes of transmission. These modes include contact, airborne, droplet, vectors, and vehicular (contaminated inanimate objects such as food, water, and fomites).
Contact Spread or Surface Spread
Contact transmission for bacteria occurs when the bacteria are transferred from one person to another through direct contact. This can happen through things like shaking hands, sharing utensils, or even touching something that someone else with the bacteria has touched. When someone touches a surface that contains bacteria, they can transfer those bacteria to their own hands. If they then touch their face, the bacteria can enter their body through their eyes, nose, or mouth.
There is also a transmission mode known as indirect contact. This includes examples such as touching a doorknob that someone with the bacteria has touched. Bacteria can live on surfaces for a surprisingly long time. Some bacteria can survive for up to a week on dry surfaces! However, the amount of time bacteria can survive on wet surfaces depends on the environment and the type of bacterium. Some bacteria can stay alive for months or even years in the water!
Contact transmission is important for the spread of many diseases, including strep throat and MRSA.
Another way that bacteria can spread is through the air. Bacteria can be released into the air when somebody coughs or sneezes. These airborne bacteria can then be inhaled by other people, causing them to become ill.
This happens because some bacteria are carried on air currents in droplet nuclei, which is commonly known as an airborne or aerosol spread. Many types of bacteria can be spread through the air, but some of the most common include Streptococcus, Staphylococcus, and Haemophilus influenza.
Consolidated or droplet spread on the other hand is one of the main ways bacteria reproduce and cause disease. Droplet spread is unique because it occurs when an infected droplet is expelled from the mouth or nose and deposited on a surface. From there, the bacteria can easily infect someone who touches the surface.
This type of transmission is responsible for many outbreaks of respiratory illnesses, such as the flu. Because these are heavier nuclei, they are not technically considered aerosol or airborne modes of transmission. Some experts consider droplet spread more similar to contact spread while others feel that it is a mode of transmission all on its own.
Vector spread for bacteria is the transfer of the pathogen from one host to another. There are many ways that this can happen, but most experts consider vector spread to be spread through insect bites. This usually takes place via the arthropod (mosquito, tick, louse) taking a blood meal from an infected host and transferring pathogens to an uninfected individual.
Vector-borne illnesses account for a significant proportion of the global disease burden and can be very serious. Some examples of vector-borne bacteria include malaria, Lyme disease, and dengue fever.
Vehicular Spread: Food or Water Contamination
The vehicular spread of bacteria refers to the spread of bacteria from one area to another via a vehicle. Vehicles of a bacterial spread most often include food, water, and fomites.
Bacteria can be spread by food and water in a few ways. Most commonly, it can be spread by food and water that have not been cooked or washed properly.
A fomite is an inanimate object that can harbor and transmit pathogens. Fomites include anything from doorknobs to towels to utensils. Common fomites in this mode of transmission are hands and skin.