Brief overview
- Description: Airborne infection with germs (e.g. bacteria, viruses) by small droplets of secretion or microparticles (aerosols) containing the pathogens.
- Transmission route: pathogens enter the air through small droplets when sneezing, coughing, or talking; another person either inhales them or the droplets land directly on mucous membranes (e.g., throat, nose, eyes).
- Diseases: Diseases that occur via droplet infection include flu-like infections, influenza (flu), covid-19, herpes, chicken pox, whooping cough, scarlet fever, diphtheria, mumps, measles, rubella.
- Prevention: keep distance from infected persons, wear masks (e.g. for Covid-19), do not sneeze or cough directly on other persons (instead in the crook of your arm).
What is droplet infection?
Depending on the droplet size, experts distinguish:
- Droplets with a diameter of at least five micrometers
- @ droplets that are less than five micrometers in size (aerosols, droplet nuclei)
Larger droplets remain in the air for only a short time due to their size and weight. Aerosols, on the other hand, hover there much longer and can also spread over greater distances. This is why we speak of actual aerogenic transmission (by air).
How are pathogens transmitted?
In an infected person, the pathogens first settle in the throat or respiratory tract and multiply. When this person sneezes, coughs, talks or breathes, small infectious droplets and particles from the respiratory tract enter the air. In the process, people who are actually ill, i.e., people with symptoms, usually excrete more pathogens than people without symptoms.
The droplets are in turn inhaled by other people or get directly onto their mucous membranes – for example in the mouth and throat, in the nose or on the conjunctiva of the eyes.
If the immune system does not defend against the pathogens at an early stage, they multiply and may cause an infectious disease.
Transmission via droplets (droplets over 5 µm)
Larger droplets have a diameter of more than five micrometers (five thousandths of a millimeter). They usually get directly onto the mucous membranes of other people through sneezing or coughing. Because of their gravity, they sink within a short distance (usually about 1 to 1.5 meters). Droplets of this size consequently remain in the air for only a short time.
Transmission via aerosols (droplets smaller than 5 µm)
Smaller droplet nuclei below five micrometers are to be distinguished from the larger droplets. These “suspended particles”, also called aerosols, are a fine mixture of solid or liquid particles like droplet nuclei in a gas (ambient air).
The smaller the droplet, the longer it hovers in the air and spreads over greater distances.
Whether and how quickly the droplets and aerosols sink or float in the air, however, depends not only on their size. Other factors such as ambient temperature, humidity and air movements (e.g. wind) also play a role.
In general, the risk of droplet infection is significantly higher in enclosed spaces where many people are present, such as schools, kindergartens, cinemas or public transport (e.g. subways or buses): the distances between people are small, and at the same time the density of droplet nuclei in the air increases rapidly.
The risk of becoming infected within a distance of about one to two meters from an infected person is greatest.
Which diseases are transmitted by droplet infection?
Droplets are mainly used to spread viral diseases, but also some bacterial diseases. Infectious diseases that occur via droplet infection with viruses include, for example:
- Influenza (flu)
- Cold diseases (flu-like infections)
- Chickenpox
- Measles
- Mumps
- Rubella
- Ringworm
- Three-day fever
- SARS
Diseases spread by droplets containing bacteria include:
- Diphtheria
- Whooping cough @
- Scarlet fever
- @ Tuberculosis
- Meningitis (meningitis, also viral)
- Legionellosis (Legionnaires’ disease)
- Plague
- Leprosy
Epidemics and pandemics – when pathogens spread in one place or globally for a limited period of time – are in most cases caused by pathogens transmitted by droplet infection.
Whether a disease actually breaks out depends on various factors, such as the physical condition or the infectiousness of the pathogen. In addition, the amount of droplets containing the pathogen that a person receives often plays a major role. For this reason, medical personnel, for example, are usually more at risk than other groups of people.
How can droplet infection be prevented?
Infection via droplets and aerosols cannot always be avoided. Nevertheless, there are some measures you can take to reduce the risk of infection.
Sneezing and coughing etiquette: Sick people protect their environment by not sneezing or coughing directly at other contacts. Instead, sneeze and cough into the crook of your arm. If time permits, you should ideally use a disposable handkerchief, which you should then dispose of quickly. It’s also best to move a bit away from bystanders or turn away.
Protective masks can help trap droplets to minimize the risk of infection from certain diseases, such as SARS or Covid-19. In this regard, larger droplets can already be well contained by surgical mouth-to-nose coverings. For even more protection, especially against aerosols containing pathogens, it is better to use FFP masks (particle-flammable half masks, usually FFP2).
Protective goggles, face shields and other protective clothing are among the appropriate measures against droplet infection, especially in medical facilities. The personnel wear the visors as additional protection to the usual masks.
A strong immune system also helps to quickly ward off pathogens. In our article “Strengthening the immune system” you will find helpful tips on how to effectively support your defenses.
Protective vaccinations are a very important part of this. They train the immune system to deal with certain pathogens, such as chickenpox or measles. If the “real” germs then reach a person via droplet infection, the immune system can react quickly and ward off the disease outbreak.
