How Germs Are Transmitted

Droplets, Contact, Airborne, and More

How germs are spread is a key factor in preventing disease, and it varies for different bacteria, viruses, and other pathogens. By understanding these modes of transmission, you can protect your health and that of the people around you.

Droplet Transmission

Droplet transmission is the usual way that cold and flu viruses and some bacteria are spread from person to person. You send droplets into the environment via your saliva and mucus when you cough, sneeze, or talk. Others can get sick when they come in contact with those infected droplets, either in the air or on surfaces where they land.

Respiratory droplets can be spread as far as 6 feet away from you. 

Droplets might enter the eyes, nose, or mouth of those who are in close proximity. Generally, they are not in the air for a long time, but can settle onto surfaces. To prevent or reduce droplet transmission, cough or sneeze into a tissue or your elbow. Then wash your hands as you can transfer these viruses to surfaces from your hands as well as from droplets.

Cold and flu viruses can remain infective on surfaces for several hours. If someone touches the surface and then touches their mouth, nose, or eyes, they may become infected. To prevent picking up viruses from surfaces, wash your hands frequently, use hand sanitizer when you don't have soap and water available, and try not to touch your face.

Airborne Transmission

In airborne transmission, a virus or bacteria is able to remain in the air for a long period of time. be distributed by airflow, and be inhaled. For this to occur, the droplet size must be very small and the germ must be able to survive being dried out. Germs capable of airborne transmission can reach the lower respiratory tract when inhaled. It may take fewer germs to set up an infection.

Fortunately, only a few germs are commonly spread by airborne transmission. These include chickenpox, measles, and tuberculosis. There is scientific debate as to whether influenza can be airborne, although most agree that droplet transmission is the usual route. When there is an outbreak of a novel pathogen, such as the coronavirus diseases COVID-19 and Middle East respiratory syndrome (MERS), researchers look closely at transmission patterns to see if it can be airborne, as this has many implications for controlling its spread.

It is much more difficult to prevent transmitting or catching airborne infections. Isolating those who are sick is an important way to control the spread. In the medical setting, negative pressure isolation rooms ensure that air is drawn into the room from the outside. The use of N95 respirators rather than surgical masks is needed to protect healthcare personnel from airborne diseases.

As N95 respirators are expensive, must be properly fitted, and users must be trained, it is important to know when they are truly needed. In the case of influenza (where there is debate about airborne spread) studies have shown it as effective for healthcare personnel to wear surgical masks as N95 respirators.

Vaccination can prevent the spread of chickenpox and measles, but there is no vaccine for tuberculosis.

Direct Contact Transmission

Close physical contact is required to transmit some diseases, as the germs can't survive for any time away from the body of a host. They are spread via saliva, wound secretions, sexual contact, or contact with blood. Sexually-transmitted diseases are in this category, as are bloodborne diseases. For other germs, this can be an additional mode of transmission (such as kissing someone who has a cold).

In daily life, safer sex practices and not sharing eating and drinking utensils, needles, or razors are steps that can be taken to prevent direct contact transmission. In healthcare settings, universal precautions including wearing gloves, masks, and washing hands can prevent direct transmission.

Indirect Contact Transmission

Some germs can live a shorter or longer time on a contaminated surface. They may be spread to surfaces via droplets or transfer of mucus, saliva, feces, or wound secretions. The objects that harbor these germs are called fomites.

Surfaces that are touched frequently by different people carry the greatest risk, such as door handles, tables, restroom surfaces, eating and drinking utensils, writing utensils, shared electronic devices, etc.

Indirect contact transmission can be prevented by handwashing after using the restroom, before and after preparing food and eating, and after touching any shared surfaces, plus not touching your face. Disinfecting these surfaces may also help.

Norovirus is a classic example of a virus spread by indirect contact. It can survive for days on surfaces.

Fecal-Oral Transmission

Contaminated food and water are the modes of transmission of many bacteria and viruses that infect the digestive system and are shed in the feces. Many kinds of stomach flu are in this category, as well as salmonella and E. coli.

Waterborne illness may result from ingesting, bathing, or swimming in contaminated water. While municipal water supplies in developed countries are rarely a risk, you might be exposed when traveling, in times of disaster, or when in a river, stream, or pond.

Foodborne illness is often due to improper hygiene. Failure to wash your hands thoroughly after using the restroom can transfer germs to food you are preparing or serving.

As well, improper hygiene can transfer fecal bacteria and viruses to surfaces, where others can pick them up and transfer them to the mouth (hence, the name fecal-oral route).

Vector-Borne Transmission

Mosquitoes, ticks, rats, dogs, and other animals can transmit some disease-causing germs to humans. In some cases, the germ must pass through the animal host before it can infect humans, such as with malaria. In those cases, it may be possible to control the spread by eliminating the mosquito vector. In others, including tick-borne Lyme disease and Rocky Mountain spotted fever, it is best to avoid the vector. Vaccination of dogs and cats can prevent the spread of rabies.

A Word From Verywell

Many types of transmission can be prevented by good health and hygiene practices. When you are sick, stay away from others, especially those most at risk of complications if they become ill. Clean the surfaces you touch as much as possible, and be diligent with handwashing. These steps can reduce the risk of spreading illness.

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